List of All Publications

Salako, F. K., P. O. Dada, Adejuyigbe, C. O. Adedire, M. O., Martins, O. Akwuebu, C. A. Williams, O. E. (2007). Soil strength and maize yield after topsoil removal and application of nutrient amendments on a gravelly Alfisol toposequence. Soil & Tillage Research 94(1): 21-35.

Vast areas of degraded soils exist in southwestern Nigeria due to topsoil removal by soil erosion and gravel/stone mining operators. The restoration of such soils has become imperative to sustain food production in most rural communities. Therefore, a factorial field experiment in three replicates of a randomized complete block design was carried out in 2003 and 2004 with the factors being slope positions (upper and lower slopes), topsoil removal (0, 15 and 25 cm depths) and nutrient amendments (0, 10 t ha(-1) poultry manure and 60:30:30 N:P2O5:K2O as NPK + urea). This was complemented with a laboratory study to determine the effects of soil water, gravel concentration and gravel size on soil strength. Maize (Zea mat's L.) was planted as a test crop to determine the effects of treatments on yield and the effect of root growth on soil strength. Soil strength was measured with a self-recording penetrometer at soil depth interval of 2.5-50 cm depth. Soil bulk density, water content, maize root and shoot biomass and grain yield were measured. In the laboratory, soil strength decreased from 483 to 314 kPa as water content increased from 0.05 to 0.62 cm(3) cm(-3) while it increased from 294 to 469 kPa as gravel concentration increased from 100 to 500 g kg(-1). Soil strength was affected more by water content and gravel concentration than gravel size. Under various moist conditions in the field, soil strength increased with soil depth from 1 177 to 5000 kPa at the upper slope and from 526 to 5000 kPa at the lower slope. Thus, the lower slope had significantly lower soil strength than the upper slope. Soil strength increased with increasing soil depth removal and was significantly reduced by poultry manure. For the 2 years of study, high grain yields were sustained with poultry manure/no topsoil removal (1784-3571 kg ha(-1)) and NPK + urea/no topsoil removal (2371-2600 kPa) at the lower slope. However, soil at the upper slope was more resistant to degradation as 16-67% loss in yield was observed compared to 65-75% for lower slope when no nutrients were applied. Nonetheless, both the upper and lower slope positions were productive with the application of poultry manure irrespective of topsoil removal, compared to NPK + urea, which was only effective without topsoil removal. Therefore, poultry manure was a better soil ameliorant than NPK + urea after topsoil removal.

Salako, F. K., P. O. Dada, Adesodun, J. K. Olowokere, F. A. Adekunle, I. O. (2007). Variation in soil strength, bulk density and gravel concentration along a toposequence in Abeokuta, south-western Nigeria. Australian Journal of Soil Research 45(8): 643-650.

This study was carried out at Abeokuta, south-western Nigeria, to understand the variation in soil strength, gravel distribution, and bulk density along a toposequence. In 2003, a 120-m transect on a fallowed land was sampled at every 1 m for topsoil bulk density measurement by excavation (3278 cm(3) pits), while soil strength was measured at every soil depth increment of 25 mm to 0.50 m depth. Total dry (rho(t)) and fine earth (16 mm. In 2006, four 100-m transects were considered; two each on adjacent fallowed and cultivated lands. Soil strength and water content were measured. The fine earth fraction of topsoil ranged from 62 to 90.6%. Gravel in the 2-4 mm class was dominant with a range of 0.8-35.7%. Thus, cores >= 50 mm could be used in the topsoil to obtain reliable estimates of bulk density. Total bulk density (rho(t)) was reduced by 4-19% when corrected for gravel to obtain rho(f). Soil strength of the lower slope was highest in 2003 (1981-4482 kPa) and lowest in 2006 (1546 kPa). In spite of the apparent signigicant influence of water content on soil strength, the relationship was weakly expressed by regression analysis, as only 35% of variation in soil strength was explained by water content at 0.10-0.15 m soil depth in 2003. No relationship was found in 2006; the cultivated segment had higher soil strength (2045 kPa) than the fallowed segment (1970 kPa) even though the water contents were similar. Also, only the 2-4 mm gravel significantly influenced rho(t). Land use, soil depth, and slope position significantly affected soil strength. Root-limiting soil strength (>2000 kPa) would certainly be encountered below 0.20 m soil depth in the wet season irrespective of land use. Management of this gravelly landscape must be based on the heterogeneous nature of soil physical properties along the toposequence, and this could be made effective by grouping the soils according to slope position and taking interest in the few portions of the landscape with extreme values of gravel distribution and high soil strength

Salako, F. K. (2006). Rainfall temporal variability and erosivity in subhumid and humid zones of southern Nigeria. Land Degradation & Development 17(5): 541-555.

Soil erosion by water is a major cause of land degradation in the tropics. Its quantitative assessment requires evaluation of factors such as rainfall variability and erosivity. Therefore, pluviograph data from 1977 to 1999 for the subhumid (Ibadan) and humid forest (Port-Harcourt) zones of southern Nigeria were analysed to determine the temporal and spatial variability of rainfall erosivity. Analyses were carried out generally at 15-minute intervals to obtain rainfall amount, duration, intensity and kinetic energy. Descriptive statistics and t-tests were used for data analyses. Rainfall intensities between 100 and 150 nun h(-1) occurred every year. Rainfall intensities were higher in the subhumid (SH) than humid forest (HF) zone whereas the kinetic energy of rainfall was higher in the HF than the SH zone. Thus, the high erosivity in the SH was mainly due to high intensities whereas it was mainly due to high amounts in the HF zone. In both zones, 42 percent of the years exceeded long-term annual average of erosivity. The mean annual EI30 was 11107 MJ mm ha(-1)h(-1) in the SH zone and 17 988 MJ nun ha(-1) h(-1) for the HF zone. Rainfall erosivity indices (E and EI30) correlated significantly with rainfall amount, with 86-99 per cent of variations in daily erosivity explained, and 55-99 percent of variations in annual erosivity explained by rainfall amount. Spatial and temporal variations were not only influenced by rainfall characteristics but also by inherent differences in rainfall erosivity indices. The data presented are required in the prevention or control of land degradation as well as in the development of watersheds, particularly in the tropics.

Salako, F. K. (2001). Structural stability of an Alfisol under various fallow management practices in southwestern Nigeria. Land Degradation & Development 12(4): 319-328.

The effects of legume-based soil management on soil dispersion were studied on an Alfisol between 1994 and 1995 in an experiment which was established in 1989 in southwestern Nigeria. The fallow systems, which constituted the main plots in the split-plot experiment, included natural fallow, Pueraria phaseoloides (Roxb.) Benth, and Leucaena leucocephala Lam de Wit. The subplots were 25, 33, 50 and 100 per cent cropping intensities. Apart from indices of soil dispersion such as water-dispersible clay and dispersion ratio, the fractal theory was applied to describe the fragmentation of soil aggregates less than 4 mm. under the systems and cropping intensities. Although water dispersible clay was less than 60 g kg(-1) in the 0-15 cm. soil depth because it was inherently low in clay content, the soil dispersion ratio was generally above 50 per cent. Also, the fractal dimensions, which ranged between 2.75 and 2.89, were similar among the fallow systems with cropping intensities for the surface soil. However, the interaction of slope position with season caused significant differences in fractal parameters, suggesting that the processes of soil degradation were different for the upper and lower slopes even with similar microaggregate distribution. The soil was inherently vulnerable to soil dispersion, although, the fallow management systems with less than 100 per cent cropping intensity would maintain soil structure at similar level as the forest

Salako, F. K. and S. Hauser (2001). Influence of different fallow management systems on stability of soil aggregates in southern Nigeria. Communications in Soil Science and Plant Analysis 32(9-10): 1483-1498.

The effects of different fallow management systems on aggregate stability were studied on an Ultisol and an Alfisol in southern Nigeria. Aggregate stability was measured in natural regrowth, and planted fallows of Pueraria phaseoloides Benth. and Leucaena leucocephala Lam de Wit in a trial established in 1989 on an Alfisol at Ibadan (7 degrees 30'N, 3 degrees 54'E), southwestern Nigeria. Soil samples (0-30 cm depth at this instance) were wetted by immersion for 2 and 10 minutes before wet-sieving at 30 rpm for 5 to 35 minutes at 5 minute increments. Mean-weight diameter (MWD), geometric mean diameter (GMD) and proportions of water-stable aggregates (WSA) were calculated. GMD and WSA were not affected by the length of pre-wetting or by the length of the wet-sieving period. Thus, wet-sieving for more than 5 minutes at 30 rpm was not necessary for these sandy soils. The trends observed for soil aggregate stability differed between the Alfisol and Ultisol, and for the Alfisol, it differed between a degraded and a managed fallow site. Thus, soil aggregate stability was influenced by soil type and soil management. The GMDs for the natural regrowth at 0-10 cm soil depth (0-15 cm soil depth sampling at 5 cm increment in this case) were between 1.12 and 1.42 mm, 1.14 and 1.46 mm for the Pueraria system, and 1.12 and 1.33 mm for the Leucaena system. An adjacent forest soil (0-10 cm) had GMDs between 1.24 and 1.54 mm. On a continuously cropped Alfisol, aggregate stability was significantly higher in the Pueraria live mulch system than in Leucaena alley cropping and natural regrowth. Fallowing for 2 or 3 years after 1 year cropping was essential under any of the systems to keep aggregate stability within the range of the forest soil. The fallow management practices enhanced surface soil aggregate stability.

Salako, F. K., O. Babalola, S. Hauser and B. T. Kang (1999). Soil macroaggregate stability under different fallow management systems and cropping intensities in southwestern Nigeria. Geoderma 91(1-2): 103-123.

Evaluation of soil aggregate stability under managed fallow systems is very relevant in the assessment of their agricultural sustainability. It is also important to identify the parameters that are most responsive to the effects of these fallow systems on aggregate stability. This study was carried out in southwestern Nigeria to quantify the effects of various fallow management systems on the macroaggregate stability of surface soil (0-15-cm depth) using a long-term fallow management trial established in 1989 on an Alfisol toposequence. Data were collected between 1994 and 1995. Three fallow systems (bush fallow, Pueraria phaseoloides, and Leucaena leucocephala) and three fallow periods (1-3 years after 1-year cropping) were evaluated. Cropping consisted of maize + cassava intercropping. A split-plot design with fellow systems as main plot and cropping intensities as subplot in four replications was used in the trial. Soil aggregate samples were wet-sieved to evaluate their mean-weight diameter (MWD) and fractal dimension (D). The means of MWD for the fallow systems and cropping intensities ranged from 2.4 to 6.4 mm. The mean D values ranged from 2.29 to 2.72 while the mean intercepts (log k) of the regression ranged from 2.01 to 2.28. Low D values (cohesive and stable aggregates) were associated with fallowing whereas high D values (fragmented aggregates) were associated with cultivation. Fallowing enhanced soil aggregate stability. The Pueraria system also enhanced soil aggregate stability more than the bush fallow and Leucaena systems when continuous cropping was practised. The subplots, which were fallowed for 2 or 3 years after 1 year of cropping, were usually similar in aggregate stability to the secondary forest soil. Fractal analysis showed further that soil aggregates in the dry season and on the upper slope of the toposequence were more cohesive than in the wet season and on the lower slope. Observed D and log k values were also significantly influenced by laboratory method

Kang, B. T., F. K. Salako, I. O. Akobundu, J. L. Pleysier and J. N. Chianu (1997). Amelioration of a degraded Oxic Paleustalf by leguminous and natural fallows. Soil Use and Management 13(3): 130-135.

The restorative ability of herbaceous (Psophocarpus palustris, Pueraria phaseoloides) and woody (Leucaena leucocephala, Senna siamea, Acacia leptocarpa, Acacia auriculiformis) legume species and of natural regrow-th was studied on an eroded and compacted Oxic Paleustalf in southwestern Nigeria. Compared to the control treatment that was continuously cropped for 15 years, four years of fallowing significantly improved test crop yields. However fallowing with the above species did not substantially improve soil properties, particularly soil bulk density. A longer fallow period may be needed to amend soil physical conditions of this degraded Alfisol. Soil chemical properties were greatly improved following land clearing and plant biomass burning in 1993. However, the residual effect of burning on soil fertility was insignificant in the second cropping year. Among the fallow species, P palustris and natural fallow-showed the best residual effect on test crop performance. Despite the high biomass and nutrient yields of S. siamea and A. auriculiformis, test crop yields on these plots were low due to the border effects from the uncleared and fallowed subplots.

Obi, M. E. and F. K. Salako (1995). RAINFALL PARAMETERS INFLUENCING EROSIVITY IN SOUTHEASTERN NIGERIA. Catena 24(4): 275-287

Rainfall erosivity was characterized for the Guinea Savanna, Forest and Coastal belts of southeastern Nigeria (4 degrees and 7 degrees N; 6 degrees 30/ and 9 degrees 30/E). The highest maximum rainfall amounts ranged from 117 to 183 mm per rain event whereas the maximum 6-minute intensities ranged from 191 mm h(-1) to 254 mm h(-1). Advanced storms were dominant in the region. The values of the Kowal and Kassam kinetic energy equation (designated E(k)) were 1.6 times higher than the values obtained using Wischmeier and Smith's equation (designated E). Compound rainfall erosivity used were the EI(30), KE greater than or equal to 25 mm h(-1), AI(m), E(k)I(30) and E(k)I(m). The mean annual erosivity values using the EI(30) index ranged from 12,814 to 18,611 MJ . mm/ha . h. The KE greater than or equal to 25 mm h(-1) ranged from 141 to 249 MJ ha(-1), the AI(m) from 849 to 1421 cm(2) h(-1), the E(k)I(30) from 16,697 to 29,610 MJ mm/ha h and E(k)I(m) from 32,752 to 62,238 MJ bullet> mm/ha . h. Rainfall erosivity approximations from rainfall amounts using indices from Roose and Arnoldus may be converted to SI units (Foster et al.) by multiplying by a factor of 17. Rainfall erosivity differences were more pronounced between the Guinea Savanna and Forest or Coastal belts than between the Forest and Coastal belts. Erosivity is higher in the Forest or Coastal belts than the Guinea Savanna belt. The high erosivity of rains in southeastern Nigeria can be attributed to heavy storms of comparatively high intensities and, often, long duration. The magnitude of rainfall erosivity provides a useful insight into the causes of the catastrophic erosion problems in southeastern Nigeria.

Salako, F. K., B. S. Ghuman and R. Lal (1995). RAINFALL EROSIVITY IN SOUTH-CENTRAL NIGERIA. Soil Technology 7(4): 279-290.

Rainfall data collected from 1986 to 1990 at Okomu (6 degrees 25'N; 5 degrees 12'E; 76 m above mean sea level), a humid forest area near Benin City, southern Nigeria, were used to evaluate erosivity characteristics, The average annual rainfall was 2048 mm and the distribution pattern was unimodal. 49% of rainfall amount fell at 7.5-minute intensifies exceeding 25 mm/h. A maximum 7.5-minute intensity of 240 mm/h was observed at the site. The median rain drop size (D-50) was 2.3 mm. The mean monthly kinetic energy, using the Wischmeier and Smith (1978) recommended procedure, ranged from 1.5 to 87 MJ/ha; whereas the values ranged from 1.5 to 140 MJ/ha using the Kowal and Kassam (1976) equation, These results suggest that equations developed in the tropics would estimate kinetic energy higher than those developed in the temperate regions. The annual value of erosivity was 18510 MJ . mm/ha . h by the EI(30) index, 216 MJ/ha by the KE greater than or equal to 25 mm/h index and 1329 cm(2)/h by the AI(m) index. The study indicates that rainfall of small and large amounts are capable of causing soil erosion at the site because they often fall at erosive intensities and contain big drops. The complementary role of the small- and large-amount storms made the cumulative erosivity of the rains at the study site very high. The information provided in this study shall be useful in estimating the erosive nature of rain in similar environments and will augment other available information in drawing an iso-erodent map for Nigeria, Furthermore, the erosivity factor for soil loss estimation on monthly basis in the area of study can be quantified by selecting the appropriate index values for soil loss equations.

Obi, M. E., F. K. Salako and R. Lal (1989). RELATIVE SUSCEPTIBILITY OF SOME SOUTHEASTERN NIGERIA SOILS TO EROSION. Catena 16(3): 215-225.

Sotona, T. Salako, FK. Adesodun, JK. 2014. Soil physical properties of selected soil series in relation to compaction and erosion on farmers' fields at Abeokuta, southwestern Nigeria. ARCHIVES OF AGRONOMY AND SOIL SCIENCE. 60, 841-857.

This study evaluated physical properties of selected soil series and their implications on the soil compaction and erosion in Abeokuta, southwestern Nigeria. Daily rainfall data (1999-2007) were collected to estimate the rainfall erosivity. Seven soil series (Iwo, Iseyin, Ekiti, Jago, Okemesi, Apomu, and Egbeda) were sampled from 0-15, 15-30, and 30-50cm depths for particle size distribution, organic carbon, pH, upper plastic limit, and compactibility (Proctor test). Microtopographical changes along and across toposequences of two farmers' fields cleared mechanically and manually, respectively, were monitored using the erosion pin method. Mean annual erosivity (EI30) was high (7646 MJ mm ha(-1) hr(-1)). Particle size, organic carbon, and pH were similar (p0.05), while upper plastic moisture was2% among different soil series. Soil-moisture density curves indicated a maximum bulk density of 1.77-1.99gcm(-3) for a moisture range of 7.6-14%; while the soils were prone to compaction at low moisture content. Microtopographic changes were found between -2 and 0cm and -8 and -2cm on mechanically and manually cleared farmland, respectively. Spatial dependence showed that the soil erosion could be predicted within 5-8m distance. To avoid erosion and compaction, soil water content should be less than 7.6% before the introduction of mechanical tillage.

Busari, MA. Salako, FK. Tuniz, C. Zuppi, GM. Stenni, B. Adetunji, MT. Arowolo, TA. 2013. Estimation of soil water evaporative loss after tillage operation using the stable isotope technique. INTERNATIONAL AGROPHYSICS. 27, 257-264.

Application of stable isotopes in soil studies has improved quantitative evaluation of evaporation and other hydrological processes in soil. This study was carried out to determine the effect of tillage on evaporative loss of water from the soil. Zero tillage and conventional tillage were compared. Suction tubes were installed for soil water collection at the depths 0.15, 0.50, and 1.0 m by pumping soil water with a peristaltic pump. Soil water evaporation was estimated using stable isotopes of water. The mean isotopic composition of the soil water at 0.15 m soil depth were -1.15 parts per thousand (delta O-18) and -0.75 parts per thousand (delta D) and were highly enriched compared with the isotopic compositions of the site precipitation. Soil water stable isotopes (delta O-18 and delta D) were more enriched near the surface under zero tillage while they were less negative down the profile under zero tillage. This suggests an occurrence of more evaporation and infiltration under conventional then zero tillage, respectively, because evaporative fractionation contributes to escape of lighter isotopes from liquid into the vapour phase leading to enrichment in heavy isotopes in the liquid phase. The annual evaporation estimated using the vapour diffusion equation ranges from 46-70 and 54-84 mm year(-1) under zero and conventional tillage, respectively, indicating more evaporation under conventional tillage compared with zero tillage. Therefore, to reduce soil water loss, adoption of conservation tillage practices such as zero tillage is encouraged.

Salako, F. K. (2010). Development of isoerodent maps for Nigeria from daily rainfall amount. Geoderma 156(3-4): 372-378.

In this study, rainfall erosivity factor, R. of the Revised Universal Soil Loss Equation (RUSLE) was estimated from daily rainfall amounts of the coastal, humid forest, savanna, semi-arid and arid zones of Nigeria using data from 17 locations, which spanned 10-33 years. Two power law equations were applied to compute the products of kinetic energy, e, and (i) maximum 30-minute intensity, I(30) (EI(30)), and (ii) maximum 15-minute intensity, I(15) (EI(15)). The indices were used to develop monthly and annual isoerodent maps. Mean monthly EI(30) ranged from 600 to 3200 MJ mm ha(-1) h(-1) whereas the annual values ranged from 3000 to 27,000 MJ mm ha(-1) h(-1) from the arid to the coastal zones. The EI(15) index was 1.7 times greater than the EI(30). Trends of rainfall erosivity in the derived, southern Guinea and northern Guinea savannas or wet savannas were erratic and less predictable from the trends of rainfall amount, unlike in the coastal, humid forest, semi-arid and arid zones. Extrapolation of data for soil conservation planning did not appear feasible in the wet savannas. Monthly values of erosivity presented are recommended for conservation plans during the cropping seasons in the various agroecological zones. The EI(15) index is recommended for both monthly (seasonal) and annual soil loss computations because short-term intensities reveal rainfall erosivity better in the tropics.

Salako, FK. 2010. Development of isoerodent maps for Nigeria from daily rainfall amount. Geoderma. 156, 372-378.

In this study, rainfall erosivity factor, R. of the Revised Universal Soil Loss Equation (RUSLE) was estimated from daily rainfall amounts of the coastal, humid forest, savanna, semi-arid and arid zones of Nigeria using data from 17 locations, which spanned 10-33 years. Two power law equations were applied to compute the products of kinetic energy, e, and (i) maximum 30-minute intensity, I(30) (EI(30)), and (ii) maximum 15-minute intensity, I(15) (EI(15)). The indices were used to develop monthly and annual isoerodent maps. Mean monthly EI(30) ranged from 600 to 3200 MJ mm ha(-1) h(-1) whereas the annual values ranged from 3000 to 27,000 MJ mm ha(-1) h(-1) from the arid to the coastal zones. The EI(15) index was 1.7 times greater than the EI(30). Trends of rainfall erosivity in the derived, southern Guinea and northern Guinea savannas or wet savannas were erratic and less predictable from the trends of rainfall amount, unlike in the coastal, humid forest, semi-arid and arid zones. Extrapolation of data for soil conservation planning did not appear feasible in the wet savannas. Monthly values of erosivity presented are recommended for conservation plans during the cropping seasons in the various agroecological zones. The EI(15) index is recommended for both monthly (seasonal) and annual soil loss computations because short-term intensities reveal rainfall erosivity better in the tropics. (C) 2010 Elsevier B.V. All rights reserved.

Busari, M. A., F. K. Salako, M. T. Adetunji and N. J. Bello (2009). Effect of selected soil amendments on physical properties of an Alfisol in Abeokuta southwestern Nigeria. Nigerian Journal of Soil Science 19(1): 93-99.

This study was carried out in 2004 and 2005 at Ajegunle Farm Settlement Scheme's site, near Abeokuta, southwestern Nigeria. A factorial experiment in randomized complete block design with 3 replicates was set up. The factors were poultry manure (0, 5 and 10 t ha -1), lime as CaCO 3 (0 and 250 kg ha -1) and NPK 15-15-15 (0 and 100 kg ha -1). Maize (TZSR-Y) was planted. Soil physical properties measured included dry bulk density, saturated hydraulic conductivity ( Ks), unsaturated water flow and clay dispersion ratio (CDR). The range of surface soil bulk density, from 1.27-1.42 g cm -3, observed for poultry manure application was significantly lower than the range of 1.39-1.48 g cm -3, when manure was not applied. The highest Ks value of 1.70 cm min -1 from plot applied with 10 t ha -1 poultry manure (PM) was significantly higher than 0.41-0.49 cm min -1 from all inorganically treated plots and the control. At the end of the second cropping season, application of poultry manure especially at 10 t ha -1 reduced the CDR from 17.1% to a range of 15.7%-9.3%, thereby increasing the soil aggregate stability. Application of 10 t ha -1 Poultry manure significantly improved the infiltration rate of the field. Integrated use of lime or 10 t ha -1 Poultry manure with NPK as well as application of 10 t ha -1 poultry manure only, improved the ability of soil to transmit water (sorptivity) under unsaturated condition. Combined application of poultry manure with inorganic amendments is therefore important in the improvement of physical properties of the soil.

Nosiru, N. A., F. K. Salako, O. Martins and N. J. Bello (2009). Potential soil erosion, river sedimentation and pollution risks from selected watersheds at Abeokuta, southwestern Nigeria. Nigerian Journal of Soil Science 19(1): 129-136.

Potential soil erosion, sedimentation and water pollution risks were assessed on the landscape of the University of Agriculture, Abeokuta, southwestern Nigeria. Potential soil loss was estimated using the Universal Soil Loss Equation (USLE) while sedimentation and pollution risks were assessed from sediment and water samples taken every 2 weeks from August-December, 2004 from five rivers. For the USLE, rainfall erosivity factor, R, was estimated using the modified Fournier index; soil erodibility was estimated using Wischmeier and Smith nomograph after analyzing surface (0-20 cm depth) soil samples from the watersheds. The topographic factor, LS, was estimated from topographic maps. Annual rainfall erosivity factor, R, was 9829 MJ mm ha -1 h -1, suggesting that Fournier index agreed with other annual R values calculated with intensity-based models for the agroecological zone. Potential soil losses ranged from 1.5-49 Mg ha -1 a -1 whereas the mean suspended sediment loads in river waters ranged from 442-1098 mg cm -3. Sediment enrichment ratio was between 0.48 and 0.64. Water quality for drinking was good based on pH, Cl -, Na + and Fe 2+ but Zn 2+ levels might not be acceptable. Also, based on these chemical properties, electrical conductivity and sodium adsorption ratio, the river waters were rated good for irrigation of crops. Watersheds in the built-up areas had the higher soil erosion and water pollution risks that those under forest. The need to adopt soil conservation measures on all watersheds was highlighted.

Salako, F. K. (2009). Isolines of rainfall kinetic energy and intensity in Nigeria. Nigerian Journal of Soil Science 19(2): 153-158.

Based on the power law equations developed by Salako (2006; 2007; 2008), daily rainfall data (generally 1988-2005) were collected from 17 weather stations in Nigeria (representing all agroecological zones in the country) to compute kinetic' energy of rainfall and IS-minute intensity, 1/5. The Wischmeicr and Smith (1978) kinetic index. EWS was similar to Brown and Foster (1987) index, E-BF. Isolines of rainfall kinetic energy and intensity were drawn with SURFER Version 8. Kinetic energy and rainfall intensity increased, generally, from the coastal region of the southeast in the northwestward direction. There were, however, abrupt changes in both characteristics between latitude 7 and 1ION, mainly in the derived, southern Guinea (SGS) and northern Guinea (NGS) savannas. Sholi-term rainfall intensities could be similar among regions in spite of significant differences in cumulative rainfall amount or kinetic energy. Kinetic energy measured at a monthly scale showed less spatial variation than that on daily scale, suggesting that long timescale could obscure useful details. Rainfall erosivity trends across the country suggest a possible influence of the migration of the Intertropical Convergence Zone (ITCZ). The maps presented can be used to decide spacing for locations of monitoring centers for soil and water management in the country.

Busari, M. A., F. K. Salako and M. A. Adetunji (2008). Soil chemical properties and maize yield after application of organic and inorganic amendments to an acidic soil in southwestern Nigeria. Spanish Journal of Agricultural Research 6(4): 691-699.

A factorial experiment with a randomised complete block design (three replicates) was performed to determine the effects of poultry manure (PM), lime (L) and NPK 15-15-15 fertilizer on soil chemical properties, and to determine the effects of their combinations on soil productivity and maize yield. The factors were PM (0, 5 and 10 Mg ha(-1)), L as CaCO(3) (0 and 250 kg ha-1) and NPK 15-15-15 (0 and 100 kg ha-1). The soil had a loamy sand texture. The application of L and PM increased the surface soil pH in a similar fashion. In both years of the experiment, the effective cation exchange capacity (ECEC) of the soil after the combined application of 10 Mg ha-1 PM, L and NPK was significantly higher than after the individual application of L or NPK or their combination (5.75-7.65 cmol kg(-1) compared to 3.36-4.57 cmol kg(-1)). The application of 10 Mg ha(-1) PM with L and/or NPK reduced the possibility of Mn toxicity, with soil levels ranging from 108 to 136 mg kg(-1). The combined use of the three amendments gave the highest leaf nutrient concentrations. The highest maize grain yield (4.62 Mg ha-1) was obtained with L + 10 Mg ha-1 PM; with no amendment the grain yield was 1.9 Mg ha-1. The application of PM enhanced the effects of L and NPK in improving soil productivity. However, separate applications of 5 and 10 Mg ha-l PM similarly affected soil productivity; the sandy nature of the soil at depths of 0-20 cm seems to have prevented differences between the two rates from becoming manifested.

Busari, M. A., F. K. Salako, Adetunji, M. A. (2008). Soil chemical properties and maize yield after application of organic and inorganic amendments to an acidic soil in southwestern Nigeria. Spanish Journal of Agricultural Research 6(4): 691-699.

A factorial experiment with a randomised complete block design (three replicates) was performed to determine the effects of poultry manure (PM), lime (L) and NPK 15-15-15 fertilizer on soil chemical properties, and to determine the effects of their combinations on soil productivity and maize yield. The factors were PM (0, 5 and 10 Mg ha(-1)), L as CaCO3 (0 and 250 kg ha-1) and NPK 15-15-15 (0 and 100 kg ha-1). The soil had a loamy sand texture. The application of L and PM increased the surface soil pH in a similar fashion. In both years of the experiment, the effective cation exchange capacity (ECEC) of the soil after the combined application of 10 Mg ha-1 PM, L and NPK was significantly higher than after the individual application of L or NPK or their combination (5.75-7.65 cmol kg(-1) compared to 3.36-4.57 cmol kg(-1)). The application of 10 Mg ha(-1) PM with L and/or NPK reduced the possibility of Mn toxicity, with soil levels ranging from 108 to 136 mg kg(-1). The combined use of the three amendments gave the highest leaf nutrient concentrations. The highest maize grain yield (4.62 Mg ha-1) was obtained with L + 10 Mg ha-1 PM; with no amendment the grain yield was 1.9 Mg ha-1. The application of PM enhanced the effects of L and NPK in improving soil productivity. However, separate applications of 5 and 10 Mg ha-l PM similarly affected soil productivity; the sandy nature of the soil at depths of 0-20 cm seems to have prevented differences between the two rates from becoming manifested.

Salako, F. K. (2008). Estimation of evapotranspiration with FAO-56 Penman-Monteith equation for three agroecological zones of Nigeria. ASSET - Series A: Agriculture & Environment 8(1/2): 134-149.

The Food and Agriculture Organisation (FAO) irrigation and drainage Paper 56 recommends the use of Penman-Monteith ( PM) method for calculating reference evapotranspiration ( ET 0 ). This method has been widely accepted. Alternative methods recommended where data requirements for the PM cannot be met are Hargreaves ( HG) and pan methods. Therefore, this study was carried out to evaluate ET0 with the PM method and develop its relationship with HG and pan methods for Onne (humid), Ibadan (sub-humid) and Kano (semi-arid), Nigeria using 1990-2005 daily climatic data. The data were resolved to daily means of each week of the year, and monthly and annual totals. Deviations of the data from long-term means were determined and the ET0 methods were compared using root mean square error ( RMSE) and mean bias error ( MBE). Autocorrelation coefficients and regression analysis were also carried out. The daily means for each week with PM ET0 ranged from 2.39-3.82 mm in Onne, 2.45-4.48 mm in Ibadan and 3.62-7.92 mm in Kano. Mean annual PM ET0 was 1130 mm vs. 2450 mm of rainfall in Onne; 1249 mm in Ibadan vs. 1286 mm of rainfall and 2007 mm in Kano vs. 786 mm of rainfall. The HG method over-predicted PM ET0 in Onne and Ibadan and under-predicted it in Kano. The pan method under-predicted it in Onne and Ibadan. Nonetheless, the HG method was a better estimator of PM ET0 in Kano than Onne and Ibadan, although daily means in the dry season were more variable. Daily means of PM ET0 were significantly related to means HG ET0 ( P

Salako, F. K. (2008). Rainfall variability and kinetic energy in Southern Nigeria. Climatic Change 86(1-2): 151-164.

A decreasing trend of rainfall has been observed in West Africa, where rainfall erosivity is also considered to be high. Therefore, this study was carried out to evaluate the variability of rainfall and its erosivity in two contrasting zones in southern Nigeria between 1977 and 1999 to understand the implications of climate variability on rainfall erosivity. The study sites were Ibadan, a sub-humid zone, and Port-Harcourt, a humid zone. Time of occurrence of rainfall, rainfall amount (A), intensity (I-15 and I-30), kinetic energy (E) and rainfall erosivity factor (R), were evaluated. Kinetic energy was estimated with Brown Foster (BF) equation, making the rainfall erosivity (product of kinetic energy and intensity) to be designated as EI30-BF and EI15-BF. The frequency of rainfall during daylight (06:00-18:00 h) was 48% for Ibadan and 69% for Port-Harcourt. There were time-specific differences in daily rainfall occurrence between the zones, suggesting a strong influence of local effects on rainfall generation, such as, relief in Ibadan and proximity to the sea in Port-Harcourt. Annual E was 213 MJ ha(-1)for Ibadan and 361 MJ ha(-1) for Port-Harcourt. Ibadan had a significantly higher daily E than Port-Harcourt because of higher intensity while Port-Harcourt had significantly higher annual E than Ibadan because of higher annual rainfall amount. Annual erosivity at Ibadan using the EI30-BF was 9,742 MJ mm ha(-1) h(-1) whereas it was 15,752 MJ mm ha(-1) h(-1) at Port-Harcourt. Using the EI15-BF, Ibadan had an annual value of 14,806 MJ mm ha(-1) h(-1) while Port-Harcourt had 20,583 MJ mm ha(-1) h(-1). Thus, annual rainfall erosivity was significantly higher in the humid than the sub-humid zone because of higher amount of rainfall but the reverse was the case with daily erosivity because of higher intensities in the sub-humid zone. Rainfall intensity was, therefore, a key measure of erosivity. There was a strong positive relationship between rainfall erosivity and rainfall amount. Between 1977 and 1988, 50-88% of the 12 years had rainfall erosivity which exceeded the long-term average but rainfall erosivity was less than the long-term average between 1989 and 1999. This suggested a decreasing trend in erosivity due to the decreasing trend in rainfall amount in West Africa. However, the trend did not imply lesser soil erosion and environmental degradation risks.

Bah A.R, Kravchuk O., Kirchhof G (2006). Impact of saturated hydraulic conductivity and rainfall on variability of predicted drainage. ASSSI - ASPAC - ACMS National Soils Conference - Soil Science Solving Problems. The University of Adelaide, North Terrace, 3-7 December 2006. Poster paper

Accurate targeting of measures to control deep drainage requires information on its spatial and temporal variability across landscapes. This is partly related to the variability of soil hydraulic characteristics and rainfall conditions. The aim of the study was to evaluate the effect of the variability of saturated hydraulic conductivity ( ) on the accuracy of drainage predicted under different rainfall conditions. Numerical studies, wherein variability within soil layers and rainfall was controlled, were conducted using a semi-mechanistic, one-dimensional water balance model (WaterMod 3). Our results suggest that the variability in significantly contribute to the variability in drainage in clay soils (>30% clay) but has little influence on that for sandy soils. It was also deduced that the soil structure should be taken into account when predicting the variation in drainage.

Beal CD, Gardner T, Kirchhof G, Menzies NW (2006) Long term flow rates and biomat zone hydrology in soil columns receiving septic tank effluent. Water Research 40, 2327-2338

Soil absorption systems (SAS) are used commonly to treat and disperse septic tank effluent (STE). SAS can hydraulically fail as a result of the low permeable biomat zone that develops on the infiltrative surface. The objectives of this experiment were to compare the hydraulic properties of biomats grown in soils of different textures, to investigate the long-term acceptance rates (LTAR) from prolonged application of STE, and to assess if soils were of major importance in determining LTAR. The STE was applied to repacked sand, Oxisol and Vertisol soil columns over a period of 16 months, at equivalent hydraulic loading rates of 50, 35 and 8 L/m2/d, respectively. Infiltration rates, soil matric potentials, and biomat hydraulic properties were measured either directly from the soil columns or calculated using established soil physics theory. Biomats 1 to 2 cm thick developed in all soils columns with hydraulic resistances of 27 to 39 d. These biomats reduced a 4 order of magnitude variation in saturated hydraulic conductivity (Ks) between the soils to a one order of magnitude variation in LTAR. A relationship between biomat resistance and organic loading rate was observed in all soils. Saturated hydraulic conductivity influenced the rate and extent of biomat development. However, once the biomat was established, the LTAR was governed by the resistance of the biomat and the sub-biomat soil unsaturated flow regime induced by the biomat. Results show that whilst initial soil Ks is likely to be important in the establishment of the biomat zone in a trench, LTAR is determined by the biomat resistance and the unsaturated soil hydraulic conductivity, not the Ks of a soil. The results call into question the commonly used approach of basing the LTAR, and ultimately trench length in SAS, on the initial Ks of soils.

Kirchhof G. (2006). Plastic Properties. In: Encyclopaedia of Soil Science 2nd revised Edition. Editor: Rattan Lal.

Application of a force to soil can result in an elastic, non-permanent, deformation that only lasts while the force is applied or a plastic, permanent deformation that persists after the load is removed. The latter may, or may not result in a decrease in the soil volume. How easily and how much the volume changes is determined by the soil's plasticity. It is an important factor influencing ease and outcome of soil tillage operations. Soil plasticity is caused by the lubricating film of water surrounding soil particles that allow the soil to change shape without rupturing upon application of forces. As an inherent soil property it is governed primarily by the surface area of the soil particles. Plasticity increases with increasing clay content, activity of clay minerals, position of the adsorbed cations in the lyotropic series and organic matter content.

Kirchhof G., So H.B. (2005). Rice Growth and Post-Rice Mungbean in Relation to Two Puddling Intensities under Glasshouse conditions. Australian Journal of Soil Research, 43, 623-628.

The effect of soil puddling on growth of lowland rice (Oryza sativa) and post-rice mungbean (Vigna radiata) was investigated using mini rice beds under controlled glasshouse conditions. Each mini rice bed was approximately 1 m3in size. Three different soil types were used: a well-drained, permeable loam; a hardsetting, structurally unstable silty loam; and a medium clay. Rice yields were reduced by low puddling compared with high puddling intensity on the loam but not affected on the heavier textured soils (silty loam and clay). Yield of mungbean was reduced on highly puddle, structurally unstable soil, indicating that puddling should be reduced on structurally unstable soils. Under glasshouse condition where crop establishment was not a limiting factor and plant available water in 0.65 m of soil was 100 mm, mungbean yields of >1 t/ha were achieved. However, under conditions where subsoil water reserves were depleted for the production of vegetative biomass during initial optimal growing condition, grain yield remained well below 1 t/ha.

Kirchhof G., So H.B. (2005). Soil Puddling for Rice Production under Glasshouse Conditions - Its Quantification and Effect on Soil Physical Properties. Australian Journal of Soil Research, 43, 617-622

The effect of soil puddling on soil physical properties of 3 different textured soils (clay, loam, and silty loam) and growth of rice (Oryza sativa) on these soils was investigated under glasshouse conditions. Puddling intensity was expressed as the ratio of soil volume subjected to the puddling implement and the total soil volume in the puddled layer, thus integrating the effects of speed and time of the puddling operation. This parameter was well related to soil dispersion, bulk density, and saturated hydraulic conductivity. However, following prolonged periods of submerged conditions during rice growth, saturated hydraulic conductivity decreased with a decrease in soil dispersion, in contrast to an expected reduction in saturated hydraulic conductivity with increased dispersion. There was indication that continuous waterlogging reduced the effect of soil puddling, in particular on heavy-textured soils.

Loetscher T, Dart P, Kirchhof G, Gray S (2005). Naiad: Sharing Lessons Learned from Innovative Urban Water Schemes. AWA Water Journal, September 2005, 60-62.

There are now numbers of innovative water projects in Australia, already implemented and planned, that serve as a testing ground for new technologies, management approaches and institutional frameworks, generating valuable experience and insights. To date, this knowledge is largely shared in an opportunistic, uncoordinated fashion. As a result, planners and practitioners alike often find it difficult to gain access to information about existing innovative water schemes and projects that could benefit the development of their own project. The Naiad project aims to change this by developing a computer program for sharing lessons learned from urban water schemes among planners, local governments, and practitioners. The project is a component of the Sustainable Water Sources program of the CRC for Water Quality and Treatment, which is carried out at The University of Queensland in collaboration with CSIRO. A preliminary version of Naiad has recently been completed. The current project stage focuses on populating its knowledge base with interesting stories about innovative water schemes.

Loetscher T, Gray S, Kirchhof G, Dart P (2005). Naiad: Sharing Lessons Learned from Innovative Urban Water Schemes. Proceedings, Australian Water Association, Ozwater Conference, Brisbane, 8-12 May 2005.

The Naiad project is a component of the Sustainable Water Sources program of the CRC for Water Quality and Treatment, which is carried out at The University of Queensland in collaboration with CSIRO. Its aim is to develop a computer program for sharing lessons learned from innovative urban water schemes among planners, local governments, and practitioners. The 2002-2003 drought, continued strong population growth in urban centres, and record low water storage levels have made sustainable water management a national priority. A paradigm shift toward water recycling and source substitution has led planners and practitioners to look for alternative solutions. Consequently, the Australian water sector is rapidly developing into a large community of practice (CoP), where sharing information and lessons learned is a key driver of innovation. There now are a number of interesting projects, already implemented and planned, that serve as a testing ground for new technologies, management approaches and institutional frameworks, generating valuable experience and insights. To date, this knowledge is largely shared in an opportunistic, uncoordinated fashion. As a result, planners and practitioners alike often find it difficult to gain access to information about existing innovative water schemes and projects that could benefit the development of their own project. This paper discusses the importance of formalising and facilitating an Australian CoP toward effectively sharing knowledge about and thereby furthering innovative water management, and it establishes the role of a tool such as Naiad in supporting this CoP. Once completed, Naiad will be a convenient interactive knowledge pool about innovative water schemes. Users will be able to query its comprehensive database with respect to a range of search criteria such as source type, type of water (re-)use, capacity, and objectives (source substitution, cost reduction, etc.). Naiad will identify schemes that match the query and display detailed information about these schemes, including treatment technologies used, cost, O&M regime, institutional framework, stakeholder consultation, risk management approach, and lessons learned. It will also include a library of guidelines and standards, and allow viewing of multimedia files, including video footage, about selected schemes. A prototype version of Naiad is currently nearing completion. This paper will present this prototype and use a case study to illustrate the type of information that will be contained in its database.

Bakti L.A.A., So H.B.; Kirchhof G. and Yatapanage K. (2003). Structural Regeneration of Puddled Soil. Proceedings, International Soil Tillage Research Organisation, 16th Triennial Conference: Soil Management for Sustainability 13–18 July 2003, The University of Queensland - Brisbane – Australia. CDrom, 59-63.

Kirchhof G. and Daniel H. (2003). A technique to assess small scale heterogeneity of chemical properties in soil aggregates. Australian Journal of Soil Research. 41, 919-932

A new method is presented which allows the separation of the soil aggregate exterior from the aggregate core. The method employs a combination of aggregate freezing with rapid separation of aggregate exteriors using ultrasonic energy. The factors influencing the thickness of the removed aggregate surface layer include water content of the aggregate prior to freezing, temperature difference between that of the frozen aggregate and that of the liquid it is submerged in during sonification, sonification time and energy, and the type of the immersion liquid. The success of the method and the thickness of the removed aggregate surface were examined using barium (Ba2+) as a tracer. Barium (as BaCl2) is rapidly absorbed by soil and is present at only very low levels in natural soils. Surface layers of 0.2–0.4 cm thickness were successfully removed from aggregates of 1–4 cm diameter. Two examples are given from soils in northern NSW to demonstrate the occurrence of small-scale hetero-geneity in soil chemical properties. Compared with the surface fraction, a 4–7% higher calcium concentration was found in the core fraction of a clay loam soil (Dermosol). Conversely, on a cracking clay soil (Vertosol), atrazine concentration was around 15 times greater in the aggregate surface fractions compared with core fractions. Compared with the traditional estimation of soil chemical properties on homogenised bulk soil samples, it is suggested that separate analysis of aggregate surface and core fractions could provide useful additional information on the relationships between soil properties and environmental responses.

Kirchhof G., and Daniells I. (2003). Soil Management Practices in Northern New South Wales Proceedings, International Soil Tillage Research Organisation, 16th Triennial Conference: Soil Management for Sustainability 13–18 July 2003, The University of Queensland - Brisbane – Australia. CDrom, 626-631.

Shelton M, Kirchhof G, Emmery P, Shehan W, Rowlings D, Poole H, Budisantoso E (2003). Leucaena as an opportunity for recharge management in northern Australia: Fitzroy Basin Case Study. 9th PUR$L National Conference (Productive Use and Rehabilitation of Saline Lands), Yeppoon Qld, 29th September to 2nd October 2003.

A revegetation strategy to prevent dryland salinity and improve water quality is proposed for the Fitzroy Basin Catchment based on planting of the perennial forage tree legume leucaena for cattle production. Scientific and grazier evidence from studies in Queensland and overseas indicates that leucaena will be effective in reducing deep drainage and runoff. Rooting depth and water use measurements are reported which indicate that leucaena will mimic the original native perennial woody vegetation. The strategy is being developed by the Leucaena Network, a grazier-based organization, in consultation with community, industry, and Government organizations. The weedy aspect of leucaena is acknowledged and is addressed by a Code of Practice for planting and management of leucaena to ensure that graziers are responsible for any weed leucaena outbreaks that occur as a result of the plantings. Direct economic benefits to the Fitzroy region from planting 250,000 ha of leucaena will be an additional 15-20,000 tonnes of beef produced per year with an internal rate of return of 28.8-38.6% to the grazier, for a total annual benefit of $7.5-15 million. Indirect economic benefits will accrue from dryland salinity risk reduction, improvement in water quality, significant amounts of carbon sequestered per year, and the cycling of biologically fixed nitrogen.

Danesh M., Daniel H. and Kirchhof G. (2002) The impact of long term crop rotations and residue management on physical properties of a northern NSW black earth (Vertosol). ASSSI National Soils Conference – Future Soils, Perth 2-6 December 2002. p50.

Warialda (along with 4 other regional sites) was selected as part of a large scale no-tillage research trial in 1981 to be representative of the major soil types for wheat production in the 600-700 mm annual precipitation range in northern N.S.W. This here presented associated study, undertaken at a time near the closure of the large no-tillage research trial, looks at the effects of different long-term (more than 20 years) crop rotations and different tillage treatments on soil physical properties that were conducted at Warialda at the University of New England McMasters Field Station. Crop rotation treatments included were A: continues wheat, C: 3 year rotation E: 2 year rotation (wheat/fababean), G: (wheat/barley/fababean). Tillage treatments included were no-tillage fallow (NT), cultivated fallow with the stubble burnt (SB) and cultivated fallow with the stubble retained (SR). Soil physical properties measured were infiltration rate, aggregate stability and total carbon content. Although several studies have been conducted in the past to evaluate the long-term effects of this type of treatments on soil physical properties, the conclusions given from those are often inconsistent. The long duration of the period of treatments in this report eliminates one of the main factors contributing to this, which is the shorter duration of previous studies.

Kirchhof G., Johnson I. and Daniel H. (2002). Variability of deep drainage - paddock leakiness hot spot. ASSSI National Soils Conference – Future Soils, 2-6 December Perth 2002. p88.

Dryland salinity is a major threat to future agricultural production in Australia. The main cause of salinisation is attributed to a change in landscape hydrology whereby water use efficient native vegetation has been replaced by less water use efficient crops or pastures (CoA 2001). Due to this change in water balance, the excess water is thought to lead to recharge of groundwater resulting in upward mobilisation of cyclic salts that were deposited into the landscape from rainfall during the past 2-3 million years (CoA 2001). Evaluation of water balances on a paddock scale generally assumes diffuse recharge. This implies that the paddock’s soil hydraulic properties can simply be described as single values varying vertically but not horizontally. Models such as SWIM or APSIM can then be employed to test under what combinations of land use and climate, recharge (=deep drainage) is minimal (Ringrose-Voase et al 2001). Resulting recommendations may include the often-advocated large-scale tree plantations to remedy dryland salinity (CoA 2001). Variation of paddock hydraulic properties is ignored although there is general acknowledgment that leakiness may vary within paddocks. The variation of this leakiness has previously not been quantified.

Soil Health Seminar – keeping our soils alive (2002). Ed. G. Kirchhof. Proceeding, Ashford 20th Feb, Lake Keepit 21st Feb. 2002. ISBN 07347 1344 4. NSW Agriculture. 182p.

Foreword: There’s an old Chinese proverb that says ‘Soil is the Mother of all Things’. Soil will always be the foundation of life. This has been a well-recognised fact until the beginning of the green revolution when we began to treat soil as a chemical reactor that needed little more than mineral fertiliser to be productive. Our life in this century focuses more and more around economic benefits, high tech machinery and microchips – and we have to relearn that we cannot reduce soil to lifeless dirt if we want to maintain our lifestyles. This is now often termed the double-green revolution, when we recognise that soil is alive and in fact the largest living organism on earth. Soil, at first sight is perhaps not as pretty and colourful as the second largest living organism, the Great Barrier Reef, but if we look closer we will discover an intimate and tremendously complex array of interconnected organisms coexisting and working within a bio-chemical environment. Professor John Doran, a renowned soil scientist from the University of Nebraska, pointed out in 1996 that there are more than 10,000 different organisms in each gram of soil and each teaspoon contains more than 1.5 times more individual organisms than there are people on earth. Aluminium is one of the major elements present in our soil and also one of the most toxic for animal and plant life. If around three grams of aluminium per cubic meter of soil is soluble, it is toxic to plants, but our soils on average contain around 70 kg per cubic meter! A functioning healthy soil system will prevent massive aluminium toxication. The production of food requires large quantities of water. For example, the grain required to produce a loaf of bread needs about 250 litres of water. If we were to untangle all visible roots to 1 meter depth in one hectare of our soils, the string would easily cover the circumference of our planet. A healthy soil will allow roots to thrive, and is easily able to supply the roots with large amounts of water. These are only a few of the fascinating accomplishments of our soil. The terms ‘soil health’ or ‘soil quality’ are increasingly being used to describe ‘the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation’ (Soil Science Society of America, Glossary 1998). For the farmer this simply means the suitability of the soil to continue to support crop growth and pasture without resulting in soil degradation or harming the environment. There is no general panacea to manage our soils. Understanding our soils is the foundation for the adoption of management practices that will maintain soil health and quality. In this seminar we will discuss soil processes with you that will put you in a position to decide on soil husbandry practices that maintain healthy soil.

Soil Health Seminar – keeping our soils alive (2002). Soil structure – the living space of our soils. Ed. G.Kirchhof. Proceeding, Ashford 20th Feb, Lake Keepit 21st Feb. 2002. ISBN 07347 1344 4. NSW Agriculture. p 161-182.

Kirchhof G. (2001). Plastic Properties. In: Encyclopaedia of Soil Science. Editor: Rattan Lal. Invited contribution, Marcel Dekker Inc.

Application of a force to soil can result in an elastic, non-permanent, deformation that only lasts while the force is applied, or a plastic, permanent deformation that persists after the load is removed. The latter may or may not result in a decrease in the soil volume. How easily and how much the volume changes is determined by the soil’s plasticity. It is an important factor influencing ease and outcome of soil tillage operations. Soil plasticity is caused by the lubricating film of water surrounding soil particles that allows the soil to change shape without rupturing upon application of forces. As an inherent soil property, it is governed primarily by the surface area of the soil particles. Plasticity increases with increasing clay content, activity of clay minerals, position of the adsorbed cations in the lyotropic series, and organic matter content.

Kirchhof G. (2001). Soil physical analysis of the core sites. In: Edwards J. Ed, WFS Results book 2nd edition. GRDC project DAN 266. NSW Agriculture Orange.

Kirchhof G. and Daniells I. (2001). Soil Structure – the key the key to sustainable agro-ecosystem management. In: Soil Health - The foundation of sustainable agriculture. Ed: R.Lines-Kelly. Wollongbar, NSW, Australia, 97-103.

So H.B, Kirchhof G., Bakker R. and Smith G.D. (2001). Low Input Tillage/Cropping Systems for Limited Resource Areas. Soil and Tillage Research. 61, 109-123.

Agriculture in limited resource areas is characterized by small farms which are generally too small to adequately support the needs of an average farm family. The farming operation can be described as a low input cropping system with the main energy source being manual labor, draught animals and in some areas hand tractors. These farming systems are the most important contributor to the national economy of many developing countries. The role of tillage is similar in dryland agricultural systems in both the high input (HICS) and low input cropping systems (LICS), however, wet cultivation or puddling is unique to lowland rice-based systems in low input cropping systems. Evidence suggest that tillage may result in marginal increases in crop yield in the short term, however, in the longer term it may be neutral or give rise to yield decreases associated with soil structural degradation. On marginal soils, tillage may be required to prepare suitable seedbeds or to release adequate Nitrogen through mineralization, but in the longer term, however, tillage reduces soil organic matter content, increases soil erodibility and the emission of greenhouse gases. Tillage in low input cropping systems involves a very large proportion of the population and any changes in current practices such as increased mechanization will have a large social impact such as increased unemployment and increasing feminization of poverty, as mechanization may actually reduce jobs for women. Rapid mechanization is likely to result in failures, but slower change, accompanied by measures to provide alternative rural employment, might be beneficial. Agriculture in limited resource areas must produce the food and fiber needs of their community, and its future depends on the development of sustainable tillage/cropping systems that are suitable for the soil and climatic conditions. These should be based on sound biophysical principles and meet the needs of and be acceptable to the farming communities. Some of the principle requirements for a sustainable system includes the maintenance of soil health, an increase in the rain water use efficiency of the system, increased use of fertilizer and the prevention of erosion. The maintenance of crop residues on the surface is paramount for meeting these requirements, and the competing use of crop residues must be met from other sources. These requirements can be met within a zonal tillage system combined with suitable agroforestry, which will reduce the need for crop residues. It is, however, essential that farmers participate in the development of any new technologies to ensure adoption of the new system.

Jayawardane, N., Kirchhof, G., Blackwell, J. (2000). Soil Slotting to ameliorate subsoil limitations to crop production. Proceedings, "Tillage at the Threshold of the 21st Century: Looking Ahead", 5th Conference of the International Soil Tillage Research Organisation (ISTRO). Fort Worth, Texas, USA, 2-7 July 2000.

Subsoil amelioration by soil slotting involves partial or segmental subsoil loosening, using rotary blades to dig trenches into the soil, similar to those created with chain type trenchers e.g.; ditch witches. These trenches, or slots are up to 100 cm deep and usually around 15 cm wide. The excavated soil is backfilled into the slots, with or without added ameliorants (gypsum, lime, fertilizer, trace elements, sludge etc…). Distance between slots depends on soil amelioration requirements, but slots are generally 1 or 2 m apart, and, if necessary crosshatched. Gypsum-slotting of sodic and slowly permeable soils improves crop production by improving soil aeration in surface layers and increasing water storage in deeper layers. Lime-slotting on acid subsoil results in greater root development to depth, and hence increased water extraction. Unlike subsoil loosening through deep ripping, slots are more resilient to re-compaction as the undisturbed soil between slots protects the loose soil from repacking during high overburden loading and wheeling. This greatly improves the longevity of the tillage effects. An important advantage of slotting over deep ripping is that soil ameliorants can be easily added to the slot and are thoroughly mixed with the soil in the slot. Incorporation of sewage sludge to depth is possible at very high rates (350 t/ha) with minimum environmental effects caused by surface runoff and erosion of the added sewage sludge. Due to the high N and P content, soil fertility of sludge-enriched slots has a dramatic effect on crop yields (300% on Barley). The organic component of the sludge can also stabilize the structure within the slot through buildup of organic matter. Water movement through the network of slots in a paddock is rapid, but waterlogging inside the slots can occur if outflow from the slots is limited and subsoil hydraulic conductivity of the non-slotted soil is low. Although slotting has been proven to provide amelioration for a range of subsoil constraints adoption at present is low, and is only economic on high value horticultural crops.

Kirchhof G. , H.B. So, T. Adisarwanto, W. H. Utomo, S. Priyono, B. Prastowo, M. Basir, T.M. Lando, Subandi, E.V. Dacanay, D. Tan-Elicano and W.B. Sanidad (2000). Growth and Yield response of Legume Crops to different Soil Management Practises after Rainfed Lowland Rice. Soil and Tillage research. 56, 51-66.

Field experiments were conducted over a 3-year period (1992–1995) in Sulawesi, East Java and the Philippines to investigate the response of post-rice (Oryza sativa L.) soil managements on growth and yield of legumes after lowland rice under rainfed conditions. Grain legume yields ranged from complete crop loss due to excessive rainfall after sowing to a maximum of 1.08 Mg ha-1 for mungbean (Vigna radiata (L.) Wilzek), 1.33 Mg ha-1 for soybean (Glycine max L. Merr.) and 2.3 Mg ha-1 for peanut (Aracis hypogaea L.). The response and magnitude of the effects from different management systems on legumes were closely related to the climatic conditions prevailing during the crop establishment phase. Correct timing of legume sowing was seen as the most important factor determining successful moderate crop production, followed by the availability of subsoil water reserves. Tillage was considered a potential method to improve yields because sowing could be carried out later during the dry season when rainfall was more predictable. Tillage, provided it is carried out at suitable soil water contents, could probably partially overcome the adverse soil physical condition induced during the rice phase. Fertiliser application tended to increase food legume in wetter areas showing that residual fertiliser effects from the previous rice crop could be limiting. In drier areas, fertiliser application had little effect on grain legume yields. Mulch as a soil amendment tended to increase yields in drier areas due to its water conservation effect. In wetter areas mulching was not necessary and could even lead to yield reduction if conditions were too wet.

Kirchhof G., S. Priyono, W. H. Utomo., T. Adisarwanto, E.V. Dacanay and H.B. So (2000). The Effect of Soil Puddling on the Soil Physical Properties and the Growth of Rice and Post-Rice Crops. Soil and Tillage Research. 56, 37-50.

Changes in soil physical properties due to traditional methods of puddling for lowland rice (Oryza sativa L.) production and post-rice legumes was investigated in field experiments conducted on three sites in Indonesia and two in the Philippines over a 3-year period. Puddling treatments used in the field were, in increasing order of puddling intensity, dry cultivation prior to submergence, one and two plowing and harrowing treatments using a draught animal and associated implements, and two cultivations using a mechanical roto tiller. Rice was followed by mungbean (Vigna radiata (L.) Wilzek) on all five sites, and in addition soybean (Glycine max L. Merr.) at Ngale and peanut (Aracis hypogaea L.) at Jambegede were also grown. All puddling treatments were followed by post-rice treatments of surface drainage (with and without surface drains) for the Indonesian sites and sowing technique (zero-till-dibble versus plough-broadcast-harrow) for the Philippine sites. Rice yields were highest under the traditional puddling techniques using draught animal traction. Results suggested that puddling with a roto tiller reduced yield because of insufficient depth of puddling, while dry cultivation may have reduced yield due to increased soil strength of the puddled layer; both are thought to limit root development. Puddling had no significant effect on post-rice mungbean and peanut production. However, results showed that increasing puddling intensity tended to reduce soybean yield. Dry cultivation of lighter textured, well drained soils such as at Manaoag, tended to require more intensive weed control in both rice and dryseason crops compared to higher puddled treatments. Weed infestation was thought to be the largest contributing factor for reduced mungbean yield at Manaoag. Increasing soil puddling intensity at Ngale and Jambegede appeared to reduce root growth. Soil water depletion tended to be smaller in the plough layer that was cultivated under wet conditions compared to pre-rice dry land preparation. Soil water extraction was small and root proliferation was up to 40 cm depth under wet conditions where plant water requirements were met from seasonal rainfall. Root proliferation was deeper and soil water use greater under dry climatological conditions. Small amounts of subsoil water use resulted in substantial yield increases ranging from 3–24 kg mm-1 of soil water used, reinforcing the important role of subsoil water storage and use by the dry season crop in this farming system.

Kirchhof, G., Daniells, I., Schwenke, G. (2000). Changing tillage methods and their effect on soil structure on major dryland cropping soils in North Western New South Wales, Australia. Proceedings, "Tillage at the Threshold of the 21st Century: Looking Ahead", 5th Conference of the International Soil Tillage Research Organisation (ISTRO). Fort Worth, Texas, USA, 2-7 July 2000.

Long term sustainability of dryland cropping in north western New South Wales (Australia) requires quality soil structure to maximise water storage and root exploration and minimise soil erosion. Soil structural decline under cropping is a well-recognised problem in this agro-ecosystem. Although there are many causes of structural decline, excessive or inappropriate tillage are major contributing factors. Soil structural decline is manifested in reduced aggregate stability, reduced macro-porosity with concomitant decreased water infiltration and increased erosion, and topsoil loss with associated exposure of sodic subsoil layers on some soils. During the past decade, the farming community has become increasingly aware of these problems. With the advent of low-cost herbicides more farmers are switching from conventional tillage to conservation or reduced tillage systems. Although research has demonstrated that conservation tillage (minimum or zero tillage) is potentially more economically and environmentally sustainable than conventional tillage (multiple cultivation operations using tyned or disked implements), it is still unclear what influence the change to conservation tillage has on soil structure in farmers fields. The objective of this study was to evaluate if changing tillage methods affect soil structural indicators on commercial dryland farms in north-western New South Wales, Australia. We inspected 40 randomly selected dryland cropping farms in north-western New South Wales to evaluate the effect of soil management practices on soil structure. Three sites were selected at each farm; two cropped sites and a never-cultivated control. Soil structural indicators measured were hydraulic properties, soil organic matter and exchangeable cations. Hydraulic conductivities at high matric potentials (-3.5 to -1.5 cm suction) were measured in situ using disc permeameters. Saturated hydraulic conductivity was measured in the laboratory on undisturbed core samples, 10 cm diameter and 7 cm height. They were taken at 3 to 10 cm and 18 to 25 cm depth. Disturbed samples were collected from corresponding depths for analysis of chemical soil analysis. Farmer’s records or recollections were used to categorise the fields according to past (more than 3 years ago) and current (the last 3 years) tillage methods. The broad categories for tillage method were conventional tillage and conservation tillage. broad categories for tillage method were conventional tillage and conservation tillage. The soil types observed on the farms were Black Earth (32% of fields surveyed), Brown Clay (15%), Duplex Soils (8%), Gradational Soils (15%) and Grey Clay (31%). Using international taxonomy, the Duplex Soils in this study tend to fall under planosols, the Gradational Soils under luvisols and candisols, the Grey and Brown Clays under chromic vertisols, and the Black Earths under pellic vertisols. On the majority of the fields (67%) conventional tillage was and still is practiced. Conservation tillage was taken up on 21% of the fields. On 10% of the fields (1/3on Black Earths and2/3 on Grey Clays) conservation tillage has always been practiced. These were all fields that were brought into cropping within the last 10 years. Fields converted to conservation tillage were all on swelling clay soils, mostly Black Earths and Brown Clays and, to a smaller extent, on the Grey Clays. Except on the Grey Clays we could not detect a significant increase in unsaturated hydraulic conductivity due to the change from conventional to conservation tillage. We observed that unsaturated hydraulic conductivity on the Grey and Brown Clays tended to be higher on the cultivated fields compared to the controls. Soil structural decline due to cultivation was most evident on the Black Earths. Saturated hydraulic conductivities of the always conventionally cultivated fields was smaller than those of the control sites, but increased when conservation tillage was adopted. Sites where conservation tillage was always practiced had the highest saturated conductivities on these soils. Soil organic carbon on the control sites was always greater than the corresponding cultivated sites regardless of whether conventional or conservation tillage was practiced. Cation exchange capacities and exchangeable sodium percentages were largely unaffected by cropping and tillage practices on the different soil types assessed in this study Of the soil types surveyed in this study, we concluded that Black Earths are most responsive to the adoption of conservation tillage. Compared to the other main soil types they are more resilient to soil structural decline due to their strong shrink-swell properties. Prolonged practice of conservation tillage on the other soil types may be required before benefits to soil structure can be observed under continuous cropping systems of this region. The results of this study also question whether cultivated soils under cropping necessarily always have inferior structure, besides lower soil organic matter, compared to never cultivated soils of this region.

Kirchhof, G., Smith, P., Hyson L. (2000). Variation in plant available water and hydraulic conductivity along transects of different textured soils. Proceedings, 5th International Conference on Precision Agriculture. July 16-19, 2000. Precision Agriculture Centre, Univ. of Minnesota, USA.

Many irrigation practices in Australia are still based on the assumption that irrigation water is plentiful and non-limiting. This has led to inefficient irrigation management with concomitant environmental problems such as increased salinity, unacceptable reduction in environmental flow and sub-optimum yields caused by over- and under irrigation. Efficient irrigation requires that land users be provided with data on plant available and readily available water. Little consistent soil information is currently available that can be used by the practitioner to optimize irrigation scheduling. Hydraulic conductivities, texture, soil water release characteristic and soil strengths were measured at 4 different depths at 5 to 7 locations along a 5 m transect on a heavy clay under irrigated cotton, and a silty clay and a silty clay loam under pasture. The results from this pilot study clearly showed that irrigation parameters, such as total and readily plant available water recommended on texture class alone are inadequate for efficient irrigation design. Variation in readily available water was greater than that of total plant available water due to the influence of soil structure at soil water contents at matric potential higher than permanent wilting point. Variation within the soil profile was greater than across the transect due to the influence of soil depth, in particular the effect of overburden pressure in swelling clay soils. However, permanent wilting point was closely related to clay content irrespective of clay type. Hydraulic conductivity underneath permanent tracks in a controlled traffic systems showed that compaction had spread laterally into the subsoil.

Rahmianna A., Sanidad W.B., Adisarwanto T., Kirchhof G. and So H.B. (2000). Crop establishment of legumes in rainfed lowland rice-based cropping systems. Soil and Tillage research. 56, 67-82.

Poor crop establishment is one of the major limitations to the production of grain legumes after rice (Oryza sativa L.) in rainfed lowland rice-based cropping systems. The success of germination and emergence of mungbean (Vigna radiata (L.) Wilzek), soybean (Glycine max (L.) Merr) and peanut (Arachis hypogaea L.) planted in zero tilled (ZT), zero tilled combined with mulch application (ZTM) and tilled soils (T) were investigated in a crop establishment trial as a function of sowing delay. Sowing delay was used as a surrogate for soil-water content. This experiment was conducted under a rain-shelter to ensure continuous and progressive drying conditions. A dibbling trial using the same legumes was conducted concurrently and subjected to the prevailing climatic conditions. Germination and emergence success rate of the traditional dibbling method was compared to dibbling incorporating depth control and seed cover. Both experiments were conducted towards the end of the 1994 rainy season in a Vertisol soil at Ngale and an Andosol soil at Jambegede, in East Java, Indonesia where the season gradually changes from wet to dry season. Mungbean emergence was 93–94% at Ngale and soybean emergence was 84–95% at Jambegede, both in the presence and absence of rain. Peanut emergence was low (50–69%) at both sites. In all three species at both sites, the percentage of seeds that failed to germinate was greater than seeds that failed to emerge, indicating that germination rather than emergence was limiting. Seed rot caused by fungal attack and poor imbibition associated with poor seed–soil contact (observed as intact seeds) were the main constraints for the success of germination of mungbean, soybean and peanut. The failure to emerge was mainly caused by seedling rot and the failure of hypocotyl and radicle to penetrate the hard soil, observed as a curling of the hypocotyl. Cultivation at Ngale on a Vertisol resulted in excessively cloddy soil, which in turn resulted in a significant decrease in germination and emergence. The application of straw mulch had little effect on the emergence of legumes on this soil. The use of depth control and application of seed–soil cover did not have a significant effect. Hence the traditional dibbling method where depth of planting ranged from 4 to 7 cm without seed cover was found to be appropriate for planting mungbean and soybean. Germination and emergence of peanut was improved with the application of soil cover and the dibbling stick had a spike added to the tip to assist the root to penetrate the hard compacted soil.

Schafer B.M. and Kirchhof G. (2000). Soil and Climate for Lowland Rice-based Cropping systems in the Philippines and Indonesia. Soil and Tillage research. 56, 15-35.

Soil morphological, physical, chemical and mineralogical properties are described at five locations in major rice (Oryza sativa L.) growing areas of the Philippines (two sites) and in Indonesia (three sites) which were selected for lowland rice-based cropping systems research. The data were used to classify the soils into the local soil series, soil taxonomy and The Australian Soil Classification systems. These data were intended to facilitate transfer of knowledge of improved farming systems technology to other lowland rice growing areas in the regions. The soils were classified as Andsisols, Inceptisols and Vertisols, and were characterised by clay contents ranging from 370 to 870 g kg-1 and cation exchange values ranging between 17 and 68 cmol (p+) kg-1 for whole soil. pH values were neutral to mildly alkaline. Land surface and root zone attributes were qualitatively evaluated for limitations to post-rice crop production by interpretation of modified surface and sub-soil properties associated with rice production. Leakiness of bunds was also examined and mainly attributed to biological activity and for the development of drainage channels. Climatic data are presented for each of the five sites and the characteristics for potential rainfall incidence are given for the post-rice dry season crop period. The soil sites selected have a range of properties which are deemed to represent large areas of soils used for rice production in these two countries.

So H.B, and Kirchhof G., (2000). Guest Editors, Special Issue: Management of clay soils for rainfed lowland rice-based cropping systems. Soil and Tillage research. 56, 188pp.

The theme of this special issue is expressed by the title of this editorial. The papers in this special issue are derived from an international conference with the same title, held in November 1995 at the Bureau of Soil and Water Management (BSWM) in Manila. The conference was sponsored and funded by the Australian Center for International Agricultural Research (ACIAR) to review and summarise the results of an international collaborative project (Project 8938) involving Indonesia, the Philippines and Australia. Also invited were scientists from a range of other countries and institutions with expertise on rice-based systems. These include scientists from the International Rice Research Institute (IRRI), the Philippine Rice Research Institute, Tamil Naidu University in southern India, and the Rice-Wheat Consortium in India, ICRISAT and the CSIRO Division of Water Resources in Griffith, Australia. The conference covered both irrigated and rainfed lowland rice-based cropping systems. Papers from the conference can be found in the edited conference proceedings published by ACIAR (Kirchhof and So, 1996). This special issue contains selected and revised papers from these proceedings, based on the outcome of the conference. Rice is the most important staple food in Asian countries. The 1994 UN Food and Agriculture Organisation (FAO) Yearbook stated that the total global area under rice was 147 million ha, and 130 million of that is in Asia. Records from the International Rice Research Institute (IRRI) in 1995 showed that the vast majority of rice is grown as paddy or lowland rice, either under irrigated (81 million ha globally, 93% in Asia) or dryland conditions (40 million ha). The most common and traditional soil management strategy for paddy rice is to puddle (wet cultivation) the soil before. rice seedlings are manually transplanted. Puddling is in fact the most important soil management practice for rice production. It serves primarily to reduce the soil's hydraulic conductivity and to ensure that inundated conditions are maintained during the cropping cycle so that weeds are easily controlled and water stress avoided. It creates a soft soil and makes transplanting of seedlings easy and allows rapid establishment of the transplanted seedlings. This system has been practised for centuries and was derived from the time when rice was a long season crop of 150 days or longer. At that time, it was essential that seeds be germinated very early to take advantage of the first rain of the season and gain time while preparing the land. It was later transplanted which allows the inundated rice crop to ®t within the rainy season. Thus, early germination is then essential to avoid terminal water stress and avoid the risk of reduced yields. However, with the modern, short season, high yielding rice cultivars, the need for early germination is no longer essential for the success of the crop. However, as old habits are not easily altered, the practice has not changed substantially despite significant efforts being invested into dry seeding of rice. Where irrigation is available, inundated conditions can be maintained to grow two or three lowland rice crops a year. Where irrigation is not available, one lowland rice crop is generally grown under rain-fed conditions during the rainy season, and only during periods where rainfall exceeds 200 mm a month. Where rainfall is erratic, the rice crop may be grown as lowland but may complete its cycle as an upland crop. It is generally accepted that inundated conditions can be maintained if rainfall exceeds the amount of water lost through evaporation (an average of 4 mm/day) and percolation which must be kept to 2 mm/day or less. Hence a primary reason for puddling is to reduce the soils' hydraulic conductivity. However, the previously puddled soil layer poses considerable restrictions on cropping after rice. Although beneficial for rice, soil puddling has an adverse effect on the physical properties of the soil. Anaerobic conditions are unfavourable for upland crop establishment and growth while the puddled layer is wet. Upon drying it becomes dry very quickly and will severely restrict root growth. Following several months of inundation during the rice phase, the subsoil water contents are generally high and except in sandy soils, it is generally sufficient to grow an upland crop with a moderate to high yield, such as legumes, provided the crop can access that water. However, yields of these dry season crops under rainfed conditions are generally very low and unreliable. Yields of mungbean of

So H.B, and Kirchhof G., (2000). Management of clay soils for rainfed lowland rice-based cropping systems. Soil and Tillage research. 56, 1-2.

The theme of this special issue is expressed by the title of this editorial. The papers in this special issue are derived from an international conference with the same title, held in November 1995 at the Bureau of Soil and Water Management (BSWM) in Manila. The conference was sponsored and funded by the Australian Center for International Agricultural Research (ACIAR) to review and summarise the results of an international collaborative project (Project 8938) involving Indonesia, the Philippines and Australia. Also invited were scientists from a range of other countries and institutions with expertise on rice-based systems. These include scientists from the International Rice Research Institute (IRRI), the Philippine Rice Research Institute, Tamil Naidu University in southern India, and the Rice-Wheat Consortium in India, ICRISAT and the CSIRO Division of Water Resources in Griffth, Australia. The conference covered both irrigated and rainfed lowland rice-based cropping systems. Papers from the conference can be found in the edited conference proceedings published by ACIAR (Kirchhof and So, 1996). This special issue contains selected and revised papers from these proceedings, based on the outcome of the conference. Rice is the most important staple food in Asian countries. The 1994 UN Food and Agriculture Organisation (FAO) Yearbook stated that the total global area under rice was 147 million ha, and 130 million of that is in Asia. Records from the International Rice Research Institute (IRRI) in 1995 showed that the vast majority of rice is grown as paddy or lowland rice, either under irrigated (81 million ha globally, 93% in Asia) or dryland conditions (40 million ha). The most common and traditional soil management strategy for paddy rice is to puddle (wet cultivation) the soil before rice seedlings are manually transplanted. Puddling is in fact the most important soil management practice for rice production. It serves primarily to reduce the soil's hydraulic conductivity and to ensure that inundated conditions are maintained during the cropping cycle so that weeds are easily controlled and water stress avoided. It creates a soft soil and makes transplanting of seedlings easy and allows rapid establishment of the transplanted seedlings. This system has been practised for centuries and was derived from the time when rice was a long season crop of 150 days or longer. At that time, it was essential that seeds be germinated very early to take advantage of the first rain of the season and gain time while preparing the land. It was later transplanted which allows the inundated rice crop to fit within the rainy season. Thus, early germination is then essential to avoid terminal water stress and avoid the risk of reduced yields. However, with the modern, short season, high yielding rice cultivars, the need for early germination is no longer essential for the success of the crop. However, as old habits are not easily altered, the practice has not changed substantially despite significant efforts being invested into dry seeding of rice. Where irrigation is available, inundated conditions can be maintained to grow two or three lowland rice crops a year. Where irrigation is not available, one lowland rice crop is generally grown under rainfed conditions during the rainy season, and only during periods where rainfall exceeds 200 mm a month. Where rainfall is erratic, the rice crop may be grown as lowland but may complete its cycle as an upland crop. It is generally accepted that inundated conditions can be maintained if rainfall exceeds the amount of water lost through evaporation (an average of 4 mm/ day) and percolation which must be kept to 2 mm/day or less. Hence a primary reason for puddling is to reduce the soils' hydraulic conductivity. However, the previously puddled soil layer poses considerable restrictions on cropping after rice. Although beneficial for rice, soil puddling has an adverse effect on the physical properties of the soil. Anaerobic conditions are unfavourable for upland crop establishment and growth while the puddled layer is wet. Upon drying it becomes dry very quickly and will severely restrict root growth. Following several months of inundation during the rice phase, the subsoil water contents are generally high and except in sandy soils, it is generally sufficient to grow an upland crop with a moderate to high yield, such as legumes, provided the crop can access that water. However, yields of these dry season crops under rainfed conditions are generally very low and unreliable. Yields of mungbean of

So, H.B., Kirchhof, G., Bakker, R., Smith, G.D. (2000). Low Input Tillage/Cropping Systems for Limited Resource Areas. Proceedings, "Tillage at the Threshold of the 21st Century: Looking Ahead", 5th Conference of the International Soil Tillage Research Organisation (ISTRO). Fort Worth, Texas, USA, 2-7 July 2000.

Agricultue in limited resource areas is characterized by small farms which are generally too small to adequately support the needs of an average farm family. The farming operation can be described as a low input cropping system with the main energy source being manual labor, draught animals and in some areas hand tractors. These farming systems are the most important contributor to the national economy of many developing countries. The role of tillage is similar in dryland agricultural systems in both the high input (HICS) and low input cropping systems (LICS), however, wet cultivation or puddling is unique to lowland rice-based systems in low input cropping systems. Evidence suggest that tillage may result in marginal increases in crop yield in the short term, however, in the longer term it may be neutral or give rise to yield decreases associated with soil structural degradation. On marginal soils, tillage may be required to prepare suitable seedbeds or to release adequate Nitrogen through mineralization, but in the longer term, however, tillage reduces soil organic matter content, increases soil erodibility and the emission of greenhouse gases. Tillage in low input cropping systems involves a very large proportion of the population and any changes in current practices such as increased mechanization will have a large social impact such as increased unemployment and increasing feminization of poverty, as mechanization may actually reduce jobs for women. Rapid mechanization is likely to result in failures, but slower change, accompanied by measures to provide alternative rural employment, might be benefcial. Agriculture in limited resource areas must produce the food and fibre needs of their community, and its future depends on the development of sustainable tillage/cropping systems that are suitable for the soil and climatic conditions. These should be based on sound biophysical principles and meet the needs of and be acceptable to the farming communities. Some of the principle requirements for a sustainable system includes the maintenance of soil health, an increase in the rain water use efficiency of the system, increased use of fertilizer and the prevention of erosion. The maintenance of crop residues on the surface is paramount for meeting these requirements, and the competing use of crop residues must be met from other sources. These requirements can be met within a zonal tillage system combined with suitable agroforestry, which will reduce the need for crop residues. It is, however, essential that farmers participate in the development of any new technologies to ensure adoption of the new system.

Bakti L.A.A., So H.B. and Kirchhof G. (1998). Changes in some physical properties of puddled soil during drying. ASSSI National Soils Conference, Brisbane, 27-29 April 1998, Conference Proceedings, 409-412.

Rahmianna A.A., So H.B. and Kirchhof G. (1998). Comparison of performance of mungbean germination obtained form the laboratory, glasshouse and field trials. ASSSI National Soils Conference, Brisbane, 27-29 April 1998, Conference Proceedings, 416-417.

Adisarwanto T., Utomo W.H., Kirchhof G., So H.B. (1996). Response of food legume crops to different soil management practises after rainfed lowland rice in east Java. IN: Management of Clay soils for Rainfed Lowland Rice Based Cropping Systems, ACIAR Proceedings No. 70, 1996, 142-147. Eds: Kirchhof G. and So H.B.

Bakti L.A.A., So H.B. and Kirchhof G. (1996). Effect of puddling on soil physical properties during rice growth. Abstracts, Joint Australian and New Zealand Soil Science Conference, University of Melbourne, 7-11 July 1996. Volume 3, Poster Papers, 13-14.

Daquiado N.P., So H.B. and Kirchhof G. (1996). Hardsetting behaviour of some Australian and Philippines Soils. Abstracts, Joint Australian and New Zealand Soil Science Conference, University of Melbourne, 7-11 July 1996. . Volume 3, Poster Papers, 57-58.

Kirchhof G. (1996). Image analysis applications in soil and crop science. ACTA Phytoecologica Sinica.

Kirchhof G. , So H.B. (1996). The effect of puddling intensity and compaction on properties, rice and mungbean growth: A mini rice-bed study. IN: Management of Clay soils for Lowland Rice Based Cropping Systems, ACIAR Proceedings No 70, 1996, 51-70. Eds: Kirchhof G. and So H.B.

Kirchhof G., So H.B., Adisarwanto T., Utomo W.H., Priyono S., Elicano D.T., Castaneda V.E. Urriza G.I.P., Alcasid G.N. jr (1996). Post rice climatic variability and legume yields. IN: Management of Clay soils for Rainfed Lowland Rice Based Cropping Systems, ACIAR Proceedings No. 70, 1996, 159-170. Eds: Kirchhof G. and So H.B.

Management of Clay soils for Rainfed Lowland Rice-Based Cropping Systems, ACIAR Proceedings No. 70, 1996. ISBN 1 86320 176 9, Eds: Kirchhof G. and So H.B., 259 p.

In Asian countries rice is the most important staple food. The most common practice for paddy rice is to puddle the soil before rice seedlings are planted. Puddling is the most important soil management strategy for rice production. Where irrigation is not available, rice is generally grown under rainfed conditions during the rainy season. It is possible for upland crops to be planted after lowland rice in rainfed areas. However, the yields are very low, and the previously puddled soil layer poses considerable restrictions on cropping after rice. Therefore, development of suitable management practices to grow food legumes after the rice crop on these puddled soils would be particularly advantageous. These proceedings are the result of a workshop held in Quezon City, Philippines in November 1995, and present the results of this research as well as papers presented on related research from the international scientific community.

Priyono S., Kirchhof G., So H.B., Utomo W.H. (1996). Effect of puddling on root growth and subsoil water use of rainfed legumes after rice. IN: Management of Clay soils for Lowland Rice Based Cropping Systems, ACIAR Proceedings No. 70, 1996, 99-108. Eds: Kirchhof G. and So H.B.

Rahmianna A.A., So H.B., Kirchhof G., Sumarno, Adisarwanto T. (1996). Crop establishment of Legumes in lowland rice based cropping systems. IN: Management of Clay soils for Rainfed Lowland Rice Based Cropping Systems, ACIAR Proceedings No 70, 1996, 109-115. Eds: Kirchhof G. and So H.B.

Rahmianna A.A., So H.B., Kirchhof G., Sumarno, Adisarwanto T. (1996). Crop establishment of legumes in lowland rice-based cropping systems. Abstracts, Joint Australian and New Zealand Soil Science Conference, University of Melbourne, 7-11 July 1996. . Volume 3, Poster Papers, 213-214.

Schafer B.M., Kirchhof G. (1996). Soil and Climate Description of Benchmark Sites for Lowland Rice-based Cropping systems Research in the Philippines and Indonesia. IN: Management of Clay soils for Lowland Rice Based Cropping Systems, ACIAR Proceedings 70, 1996, 29-50. Eds: Kirchhof G. and So H.B.

So H.B., Kirchhof G., Utomo W.H, Adisarwanto T., Prastowo B., Dacanay E.V., Alcasid G.N. jr. And Ringrose-Voase A.J. (1996). Management of Clay soils for lowland rice-based cropping systems: The Experiments and Methodology. IN: Management of Clay soils in Lowland Rice Based Cropping Systems, ACIAR Proceedings No. 70, 1996, 25-28. Eds: Kirchhof G. and So H.B.

So. H.B., Kirchhof G., Ringrose-Voase A. (1996). Management of clay soils for rainfed lowland rice-based cropping systems. Abstracts, Joint Australian and New Zealand Soil Science Conference, University of Melbourne, 7-11 July 1996. . Volume 3, Poster Papers, 235-236.

Utomo W.H., Prastowo B., Adisarwanto T., Dacanay E.V, Kirchhof G., So H.B.(1996). Soil Puddling and Rice growth. . IN: Management of Clay soils in Lowland Rice Based Cropping Systems, ACIAR Proceedings No. 70, 1996, 90-94. Eds: Kirchhof G. and So H.B.

Jayawardane N.S., Barrs H.D., Muirhead W.A., Blackwell J., Murray E. and Kirchhof G. (1995). Lime slotting technique to ameliorate sub-soil acidity in a clay soil. II Effects on medic root growth, water extraction and yield. Australian Journal of Soil Research. 33, 443-459.

Subsoil acidity causes low crop production, which is often associated with shallow root development and restricted soil water extraction. In part I of this series, lime-slotting of an acid soil was shown to improve the soil physical and chemical characteristics for root growth. In a lysimeter study on an acid soil, the effects of several soil ameliorative treatments on root growth, water extraction and yields of a medic crop were evaluated. Large lysimeter cores of 0.75 m diameter and 1.35 m deep were used. The soil treatments included a non-ameliorated acid soil, lime-slotting with a 0.15 m wide and 0.8 m deep slot containing 20 t ha-1 of lime, lime-slotting combined with surface phospho-gypsum application at 10 t ha-1, and complete amelioration of the entire soil volume by mixing lime at 133 t ha-1 and repacking to a low bulk density of 1.1 t m-3. In the non-ameliorated acid soil, medic roots were confined to the surface (0.1 m) layer, resulting in limited water extraction of 32 mm during a prolonged drying cycle, and a low dry matter yield of 70 g m-2. In the lime slotted soil, roots grew within the slot to its full depth, although penetration into the undisturbed soil was restricted to the soil immediately adjacent to the slot. Consequently, the root length per unit surface area (La) at depths below 0.1 m depth was increased to 9.9 km m-2. During a drying cycle, water extraction increased to 58 mm. The increased water extraction came from both the slotted soil and the undisturbed soil between slots. This led to an increase in dry matter yields to 270 g m2. In lime-slotted soils with surface gypsum applications, the root growth and crop water extraction patterns were similar to the lime-slotted soil. Repacking limed soil resulted in similar root lengths (L(a) 10.0 km m-2) as lime-slotted soil. However, owing to more uniform distribution of roots in the repacked soil, water extraction was increased to 100 mm and yields increased to 590 g m-2. Yields of non-ameliorated soil were only 12% of the repacked, limed soil. However, lime-slotting which involves loosening only 25% of the soil surface area and addition of only one-sixth of the amount of lime required for complete soil amelioration, led to marked increases in yield (46% of the yield of repacked soil). Future field studies are required to evaluate the optimum limed-slot configurations required for different soils, crops and climatic regimes.

Jayawardane N.S., Blackwell J., Kirchhof G. and Muirhead W.A. (1995). Slotting - A deep tillage technique for ameliorating sodic, acid and other degraded subsoils and for land treatment of waste. Advances in Soil Science. (Lewis publishers). p 109-146.

Kirchhof G. and So H.B. (1995). Compaction on Vertisols: Can it be predicted? National Controlled Traffic Conference. Rockhampton, 13-14 September 1995, Proceedings. 196- 201.

Kirchhof G. and So H.B. (1995). Legumes after rainfed lowland rice. ACIAR Food Legume Newsletter No 22, April 1995, p 2-5.

Kirchhof G., Blackwell J., Hughes M., Parsons D.H. and Jayawardane N.S. (1995). Increasing cane yield by reducing both waterlogging and water stress. Final report to the Sugar Research and Development Cooperation. ISBN No 0 643 05780 3, 59p.

Kirchhof G., Jayawardane N.S., Blackwell J. and Murray E. (1995). Lime slotting technique to ameliorate sub-soil acidity in a clay soil. I Effects on soil pH and physical characteristics. Australian Journal of Soil Research. 33, 425-441

In soils with subsoil acidity, root growth of plants sensitive to acidity is restricted to surface layers resulting in reduced water and nutrient uptake and low yields of crops. In the present study, the use of the lime-slotting technique, with slots 0.15 m wide and 0.8 m deep, for providing long-term improvements of the adverse soil chemical and physical characteristics of an acid, clay soil was investigated. Lime-slotting using a rotary slotter resulted in a uniform increase in soil pH to the full depth of the slot (0.8 m), indicating a thorough mixing of the lime with the small soil fragments produced by slotting, as they are thrown up into the rotor shroud and redeposited in the slot. In contrast, ripping to 1.0 m depth and delve ploughing to 0.8 m depth only changed the soil pH close to the soil surface. The saturated hydraulic conductivity, total porosity and air-filled porosity at a potential of - 10 kPa measured on soil cores was significantly (P

Adisarwanto T., Utomo W.H., Kirchhof G. and So H.B. (1994). The effect of soil management practises on soybean after lowland rice on Vertisol. Proceedings, World Soybean Research Conference V, 21-27 February 1994, Chiang Mei, Thailand, 6pp.

Kirchhof G. (1994). Compaction Properties of Vertisols and their potential effect on sunflower. PhD thesis, Univ. of Qld.

Large areas of arable land in the eastern inland regions of Australia are dominated by cracking clay soils (Vertisols). The occurrence of compaction on these soils and its effect on crops is not well understood. This work investigated the effect of compaction on the growth and development of sunflowers and the response of a range of cracking clay soils to compactive forces. Compaction on Vertisols was expressed as bulk density corrected to a reference water content assuming the soil undergoes normal shrinkage. This presents a useful technique to quantify compaction of Vertisols in the field. Field experiments were carried out on a Vertisol (black earth) at the University of Queensland, Gatton College at Lawes, to investigate the effect of compaction on the growth of sunflowers and its influence on soil water contents during two growing seasons in 1984/85 and 1985/86. Treatments included an uncompacted control, low compaction and severe compaction. The uncompacted treatment was achieved by deep ripping to 40 cm followed by fallowing for several months. Compaction was induced using a road roller with a contact pressure of 100kPa; 1 pass and 4 passes with the roller were used for low and severe compaction respectively. In both years the compaction treatments were applied before sowing. A third experiment was conducted in 1985/86 on the site compacted in the previous year without re-inducing the compaction treatments to investigate the residual effects of compaction after self-amelioration of the soils in the absence of machinery traffic. In both years severe compaction reduced the early growth of the crop and amount and depth of water depletion was decreased. However, as the season progressed differences between treatments decreased. Final seed yields were reduced by 15% in 1984/85 under high compaction. This was related to bulk density values exceeding 1.39Mgm-3(at 0.3 gg-1) below the cultivated layer at 20 to 25 cm depth. Compaction only affected plant growth when it was induced at the start of the cropping season. Wetting and drying cycles over the period of one year in the absence of machinery traffic did eliminate soil compaction in the field experiments of this study. The response of clay soils to compactive forces was evaluated in the laboratory for soils found in major cotton growing areas in Queensland. A total of 70 sites were sampled from a wide range of soil types with clay contents varying from 30 to 73%, organic C from 0.8 to 5.7% and dispersible clay contents from 2 to 22%. Atterberg limits, water content at permanent wilting point, exchangeable cations and clay content of the soils used were strongly related and could be predicted from each other. of the soils used were strongly related and could be predicted from each other. A uni-axial compression test, using pressures and loading times similar to those occurring during the passage of agricultural vehicles, was developed and used to determine the response of these soils to compaction at different soil water contents. It was expressed using the relationship of bulk density to the soil water content at which compaction was carried out (compaction curves). Bulk density values reached a maximum value at an optimum water content depending on the magnitude of the compactive pressure applied. It was increased as uni-axial pressures increased and clay content decreased. Organic carbon decreased bulk density but its effect was small. The bulk densities at maximum compaction as well as bulk densities at water contents lower than the optimum water content were related to applied pressure, texture and water content at which the soil was compacted and could be predicted with a high degree of reliability. The equation for bulk density at water contents less than the optimum is: Bd = 1.425 - 0.986 clay + 0.144 ln p + 0.530 Wg n = 507, r2 = 0.71 and where Bd = bulk density [Mgm-3] clay = clay content [gg-1] p = uni-axial pressure [kPa 10-2 (Bar)] Wg = gravimetric water content [gg-1] This equation should be able to be developed into useful field model and a management tool. ation should be able to be developed into useful field model and a management tool. The potential effects of compaction on soil productivity were associated with the change in the soil pore size distribution. Compaction reduced the volume of large pores and slightly increased the volume of small pores. This resulted in slightly lower amounts of plant available water but a strong decrease in saturated hydraulic conductivity in soils at high bulk density values. Compaction can be expected to become harmful to crop growth when a threshold bulk density was exceeded. The threshold bulk density for growth and yield of sunflower on vertisols (black earths) at the University of Queensland, Gatton College at Lawes was 1.39 Mgm-3 (corrected to a water content of 0.3 gg-1). This value was close to that of maximum compaction achievable corresponding to an air filled porosity of about 6% which is likely to be simular for other vertisols and crop types.

Kirchhof G. and So H.B. (1994). Soil puddling for rice production and its effect on soil structure and water percolation. Proceedings, International Symposium on Sealing, Crusting and Hardsetting Soils: Productivity and Conservation. Brisbane, Qld, Australia; The University of Queensland, 7-11 February 1994, 413-419.

Puddling intensity was quantified and expressed as the ratio of puddled soil volume versus total soil volume. This expression integrated the effects of speed, time and shape of the puddling implement and was well related to soil dispersion, bulk density and saturated hydraulic conductivity. Following prolonged periods of submerged conditions during rice growth, saturated hydraulic conductivity decreased despite a concomitant reduction in soil dispersion. There was indication that continuous water logging reduced the effect of soil puddling, in particular on heavy textured soils. Heavy textured soils also appeared to recover more readily from soil structural deterioration from soil puddling than lighter textures soils after one or more drying cycles.

Kirchhof G., Alcasid Jr. (1994). Management of clay soils for lowland rice based cropping systems. The Philippine Journal of Crop Science, Volume 19, Supplement 1, May 1994. p53.

Kirchhof G. and Pender C. (1993). SCI-SCAN image analysis system - Manual, Image Analysis made easy (187pp). Note: There are two version of the SCI-SCAN manual. This has now been replaced with the commercial version by Delta-T, edited by Dr Nick Webb.

So H.B. and Kirchhof G. (1993). Management of Clay Soils under Low-land Rice Based Cropping Systems. ACIAR Food Legume Newsletter No 18, April 1993, p 7-8.

So H.B. Kirchhof G. and Basnet B.B. (1993). Soil Physics Laboratory Manual, Department of Agriculture, The University of Queensland, St Lucia Qld. 4072, 98 pp

Blackwell J., Jayawardane N.S., Kirchhof G. and Smart R. (1992). Use of sludge-Slotting to dispose of and utilise Sewage and other waste on agricultural land. CSIRO Division of Water Resources, Divisional Report 92/4. Eds: K.H. Bowmer and P.Laut, Seeking Solutions, 19 - 21.

Kirchhof G. (1992). Measurement of root length and thickness using a hand held computer scanner. Field Crops Research. 29, 79-88.

A hand-held computer scanner was used to produce images of lines randomly drawn on a sheet of paper which could simulate roots. The binary images were analysed for total length using the intercept method and distribution of line thicknesses. The number of intercepts was normalized with respect to image size and resolution. This value, in conjunction with the fraction of line cover in the image, was used to obtain an equation to predict length (normalized with respect to picture size) from number of normalized intercept counts. The derived calibration equation (r2=0.008, cv=1.7%) predicted the length irrespective of thickness and distribution of thickness. The intercept method was extended to determine the length of lines with different thicknesses within the image. It was possible to resolve line thickness differences of 0.15 mm for thicknesses ranging from 0.15 to 0.7 mm. Although the total length, determined as the cumulative length of all thickness intervals, was lower than the real total length, the relative distribution of thicknesses was accurate to 2%. From length and thickness of lines in each interval, its surface area could be calculated, assuming a cylindrical shape. The major advantages of using a hand-held scanner for root length determinations are: (i) very low cost, compared to other image analysis systems; (ii), high resolution (>0.063 mm); (iii) actual size of the image is automatically recorded; (iv) small size of the scanner; and (v) image size is independent of the video screen size.

Kirchhof G., Pender C., Daniel H. (1992). The use of computer scanners for image analysis in soil science and Agronomy. Abstracts, National Soil Conference, Adelaide, Australia, 19-23 April 1992. p 152.

Jayawardane N.S., Blackwell J., Muirhead W.A., Kirchhof G. and Smart R.E. (1991). Gypsum and lime slotting - A new deep tillage technique for improved crop production on sodic and acidic soils. Soil Tillage and Agricultural Sustainability, Proceedings, 12th International Conference, ISTRO. Ibadan, Nigeria 8-12 July 1991.

Kirchhof G, Blackwell J., Rawlinson L. and Walsh J. (1991). Use of soil slotting to incorporate sludge as a soil ameliorant. AWWA/WPCF Joint Residuals Management Conference, 'Residuals Management after 1991'. Durham, NC, August 11-14, 1991.

Kirchhof G., Blackwell J. and Smart R.E. (1991) Growth of vineyard roots in segmentally ameliorated acid subsoils. Plant and Soil, 134, 121-126. ALSO IN: Plant Soil Interactions at low pH, Edt. by R.J.Wright et al., June 1991, 447-452.

Grapevine growth and production is limited in the Port Macquarie region by acidic subsoils and high exchangeable aluminium. Root growth is restricted to about 15 cm depth, and despite high growing season rainfall (920 mm, September to March) which exceeds predicted evapotranspiration for the period (400 mm), the vines suffer periodic water stress. Slotting is a technique of subsoil amelioration allowing thorough incorporation of lime to depth. Slots are 150 mm wide, and in this experiment were installed to 400 mm depth. The aim of slotting is to improve root growth in the subsoil, thus increasing plant access to water and nutrients previously inaccessible. The experiment was conducted in a Chardonnay vineyard planted in 1982. Lime was incorporated into the slots at about 2 t ha 1 with a further 8 t ha -1 spread on the surface, mixed and moved to form an under vine bank. Soil and root samples were taken in February, 1990. Slotting caused pH(CaCl2) to increase from 4.3 to 5.0 to 400 mm depth. Associated with this was a more than ten-fold increase in root length density. The slotting technique gives the opportunity to improve dense, poorly drained acidic soils and make them suitable for horticulture production.

Smart R.E., Kirchhof G. and Blackwell J. (1991). The diagnosis and treatment of acidic vineyard soil. Wine Industry Journal, Feb.1991, 35-40.

Blackwell J., Kirchhof G., Smart R.E. and Jayawardane N. (1990). (Article on soil slotting in vineyards) Good fruit and vegetables, Oct. Ed.

Kirby M. and Kirchhof G. (1990) The compaction process and factors affecting soil compactibility. Soil Compaction Workshop, Toowoomba, 15 - 17 Oct 1990, 28-31

Kirchhof G., Blackwell J. and Smart R.E. (1990) Growth of vineyard roots in segmentally ameliorated acid subsoils. 2nd international symposium on Plant-Soil Interactions on Acid Soils. West Virginia (Abstract p.97)

Kirchhof G., Jayawardane N.S., Blackwell J. and Muirhead W.A. (1990). Amelioration of acidic subsoils. Proceedings 5th Australian Soil Conservation Conference - Stable Cropping systems - Geralton, W.A., 49-55.

Kirchhof G. and So H.B. (1989). The compactibility of clay soils (Vertisols). Abstracts, Soil compaction as a factor determining plant productivity, International Conference, 5 - 9 June 1989, Lublin Poland, 91-92.

Kirchhof G. and So H.B. (1988). Susceptibility of clay soils to compaction. Abstracts, Australian National Soils Conference. Canberra. p.207.

Kirchhof G., Schafer B.M. and So H.B. (1988). Compactibility of soils used for cotton production. 4th Australian Cotton Conference, Surfers Paradise, August 17th & 18th.

Kirchhof G. and So H.B. (1987). A Uni Axial compression test to determine compaction properties of soils. National Soil Physics Workshop. Toowoomba. 151-153a.

Kirchhof G., Schafer B.M. and So H.B. (1986). The effect of compaction on the growth and yield of sunflowers. Proc. 6th Austr. Sunflower Conference, Gunnedah. 62-66.

Kirchhof G.(1984). Soil physical changes in a duplex profile during a drying cycle. Dipl.Ing.agr. Thesis. Univ. of Hannover (FRG).

Muirhead W.A., Kirchhof G. and White R.J.G. (1984). Soil physical changes in a duplex profile during a drying cycle. CSIRO Div.of Irrigation Research, Griffith NSW, Annual Report 1983/84, 55-56.

Salako F.K. and Kirchhof G. (2003). Field hydraulic properties of an Alfisol under various fallow systems in southwestern Nigeria. Soil Use and Management. 19, 340-346.

The effects of various fallow management systems and cropping intensities on water infltration were measured on an Alfisol at Ibadan in southwestern Nigeria. The objective was to determine the influence of the land use systems (a combination of crop±fallow sequences and intercropping types) on soil hydraulic properties obtained by disc permeameter and double-ring infiltration measurements. The experiment was established in 1989 as a split-plot design with four replications. The main plots were natural fallow, planted Pueraria phaseoloides and planted Leucaena leucocephala. The subplots were 1 year of maize/cassava intercrop followed by 3-year fallow (25% cropping intensity), or 2-year fallow (33% cropping intensity), or 1-year fallow (50% cropping intensity), or no fallow period (100% cropping intensity). Water infiltration rates and sorptivities were measured under saturated and unsaturated flow. Irrespective of land use, infiltration rates at the soil surface (121±324 cm h±1) were greater than those measured at 30 cm depth (55±144 cm h±1). This indicated that fewer large pores were present below 30 cm depth compared with 0±30 cm depth. Despite some temporal variation, sorptivities with the highest mean value of 93.5 cm h-1 increased as the cropping intensity decreased, suggesting a more continuous macropore system under less intensive land use systems. This was most likely due to continuous biopores created by perennial vegetation under long fallow systems. Intercropped maize and cassava yields also increased as cropping intensity decreased. The weak relationship between crop yields and hydraulic conductivity/infiltration rates suggests that the rates were not limiting.

Salako, F. K. and G. Kirchhof (2003). Field hydraulic properties of an Alfisol under various fallow systems in southwestern Nigeria. Soil Use and Management 19(4): 340-346.

The effects of various fallow management systems and cropping intensities on water infiltration were measured on an Alfisol at Ibadan in southwestern Nigeria. The objective was to determine the influence of the land use systems (a combination of crop-fallow sequences and intercropping types) on soil hydraulic properties obtained by disc permeameter and double-ring infiltration measurements. The experiment was established in 1989 as a split-plot design with four replications. The main plots were natural fallow, planted Pueraria phaseoloides and planted Leucaena leucocephala. The subplots were 1 year of maize/cassava intercrop followed by 3-year fallow (25% cropping intensity), or 2-year fallow (33% cropping intensity), or 1-year fallow (50% cropping intensity), or no fallow period (100% cropping intensity). Water infiltration rates and sorptivities were measured under saturated and unsaturated flow. Irrespective of land use, infiltration rates at the soil surface (121-324 cm h(-1)) were greater than those measured at 30 cm depth (55-144 cm h(-1)). This indicated that fewer large pores were present below 30 cm depth compared with 0-30 cm, depth. Despite some temporal variation, sorptivities with the highest mean value of 93.5 cm h(-1/2) increased as the cropping intensity decreased, suggesting a more continuous macropore system under less intensive land use systems. This was most likely due to continuous biopores created by perennial vegetation under long fallow systems. Intercropped maize and cassava yields also increased as cropping intensity decreased. The weak relationship between crop yields and hydraulic conductivity/infiltration rates suggests that the rates were not limiting.

Kirchhof, G., Salako F.K. (2000). Residual tillage and bush-fallow effects on soil properties and maize intercropped with legumes on a tropical Alfisol. Soil Use and Management. 16, 183-188.

After six years of bush-fallow, residual effects on soil productivity of tillage practices prior to the fallow were investigated on an Alfisol in southwestern Nigeria. In 1996 fallow was followed by maize intercropped with cover crops of Pueraria phaseoloides, Mucuna pruriens or cowpea (Vigna unguiculata) and no intercrop. Parameters measured included soil properties, ground cover, crop growth and yield, rainfall erosivity, runoff and soil loss. In spite of six-years of bush-fallow and establishment of cover crops, soil erosion was significantly greater on plots that had been conventionally cultivated previously using disc ploughs, harrows and mechanical rotovators (1.78 t ha71season71) compared to previously no-till plots (1.34 t ha-1season-1). Crop growth and yields were least and soil loss greatest (2.83 t ha-1season-1) on the previous bare plot. Maize grain yield was highest using Pueraria phaseoloides as an intercrop (2.15 t ha-1) followed by a cowpea inter-crop (1.92 t ha-1), maize without intercrop (1.87 t ha-1) and Mucuna pruriens intercrop (1.71 t ha-1). The maize grain yields reflected levels of competition from the cover crops. Cowpea-maize intercrop may be most suitable for farmers because maize yields were satisfactory and cowpea grain serves as additional subsistence. Cowpea yields were 390 kg ha-1. Soil erosion was also moderate using cowpea as an intercrop (1.71 t ha-1season-1). However, Pueraria phaseoloides gave the best erosion control with a soil loss of 1.34 t ha-1 season-1

Kirchhof G. and Salako F.K. (1998). Residual Tillage Effects and soil erosion after bush fallow on a tropical Alfisol in a legume based intercropping system. ASSSI National Soils Conference, Brisbane, 27-29 April 1998, Conference Proceedings, 47-55.

The effects of pre-fallow tillage practices on the productivity of a 6 year fallowed tropical Alfisol was investigated in South Western Nigeria. Post-fallow land use in 1996 was maize production intercropped with legume. The parameters evaluated included soil properties, ground cover, crop growth and yield, rainfall erosivity, runoff and soil loss. In spite of the six-year bush fallow and establishment of cover crops, soil erosion was significantly higher on plots previously under conventional tillage compared to no - tillage plots. Crop growth and yields were low on the previous bare plot which had maximum erosion compared to the previously cropped plots in spite of bush fallowing. Maize grain yield was highest under Pueraria phaseoloides intercrop (2.15 t/ha) followed by Cowpea intercrop (1.92 t/ha), sole maize (1.87 t/ha) and Mucuna pruriens intercrop (1.7 t/ha). Soil erosion was moderate under this system. However, Pueraria performed best as an intercrop for soil conservation in this first year of intercropping.

Salako EK, Olowokere EA, Tian, G Kirchhof, Osiname O. (2007). Ground cover by three crops cultivated on marginal lands in southwestern Nigeria and implications for soil erosion. Spanish Journal of Agricultural Research. 5, 497-505.

Resource-poor farmers in developing nations cultivate marginal lands, thereby exacerbating the problem of soil degradation through poor plant growth and ground coverage. An assessment of ground cover under such a practice will provide a guideline for soil conservation. Ground cover by leguminous cover crops (e.g., Mucuna pruriens, Pueraria phaseoloides and Vigna unguiculata), associated with yam, maize and rice was measured in three different experiments in southwestern Nigeria using beaded-string method while leaf area was measured using a flat-bed scanner. The leaf area was used in obtaining equivalent of ground cover fraction from the leaf area index. Ground cover by yam was

Salako F.K, Tian G., Kirchhof G., Akinbola G.E. (2006). Soil particles in agricultural landscapes of a derived savanna in southwestern Nigeria and implications for selected soil properties. Geoderma, 137, 90-99.

The vast area of savanna ecology in Africa plays a significant role in food production, making a study of soils in this zone very important. Therefore, soil physical and chemical properties of 14 soil profiles were studied in a derived savanna zone of southwestern Nigeria on 2 toposequences at 2 locations (Ibadan and Alabata), which were 20 km apart. Six soil profiles were studied at Ibadan while 8 were studied at Alabata. Morphological descriptions of profiles were carried out. Data collected included particle size distribution, bulk density, clay dispersion, water retention characteristics, pH, organic carbon, exchangeable K, Ca, Mg and available P. Soil profiles along the toposequences were well developed with depths exceeding 180 cm, except for one profile at the lower slope position where an indurated plinthic layer was found at 68 cm depth. The horizons were easily distinguished with color, texture and consistency. Total sand, with the main component being coarse sand, decreased with depth from 813 to 502 g kg-1 at Ibadan and from 824 to 635 g kg-1 at Alabata. The clay content increased with depth from 54 to 356 g kg-1 at Ibadan and from 63 to 279 g kg-1 at Alabata. Gravel concentration was highest for soil horizons found between 20 and 102 cm depth. Also, bulk density increased with soil depth from 1.35 to 1.51 g cm-3 at Ibadan and from 1.38 to 1.64 g cm-3 at Alabata, indicating that subsoil horizons were more compact due to higher clay and gravel contents, and sticky consistency. The A horizon had a significantly higher water content at water potentials N2 kPa while the subsoils had higher water content at b2 kPa. Soil organic C and total N decreased with soil depth at both locations with the A horizon having significantly higher organic C (7.10–12.69 g kg-1) and total N (0.84–1.2 g kg-1) than deeper horizons (1.9–4.47 g kg-1 for organic C and 0.12–0.58 g kg-1 for N). Particle size distribution was significantly different among the slope positions at both locations. Also, soil water retention, soil pH, total N and exchangeable K were distinguishing parameters among slope positions. The interaction of soil depth and slope position was, however, not significant suggesting that processes influencing soil horizon development acted independently in the vertical and lateral directions. Soil pH was the only attribute that distinguished the toposequences between the two locations.

Salako F.K., Kirchhof G., Tian G. (2006). Management of a previously eroded tropical Alfisol with herbaceous legumes: Soil loss and physical properties under mound tillage. 89, 185-195.

A study was carried out on a previously eroded Oxic Paleustalf in Ibadan, southwestern Nigeria to determine the extent of soil degradation under mound tillage with some herbaceous legumes and residue management methods. A series of factorial experiments was carried out on 12 existing runoff plots. The study commenced in 1996 after a 5-year natural fallow. Mound tillage was introduced in 1997 till 1999. The legumes – Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides – were intercropped with maize in 1996 and 1998 while yam was planted alone in 1997 and 1999. This paper covers 1997–1999. At the end of each year, residues were either burned or mulched on respective plots. Soil loss, runoff, variations in mound height, bulk density, soil water retention and sorptivity were measured. Cumulative runoff was similar among interactions of legume and residue management in 1997 (57–151 mm) and 1999 (206–397 mm). However, in 1998, cumulative runoff of 95 mm observed for Mucuna-burned residue was significantly greater than the 46 mm observed for cowpea-burned residue and the 39–51 mm observed for mulched residues of cowpea, Mucuna and Pueraria. Cumulative soil loss of 7.6 Mg ha 1 observed for Mucuna-burned residue in 1997 was significantly greater than those for Pueraria-mulched (0.9 Mg ha-1) and Mucuna-mulched (1.4 Mg ha-1) residues whereas in 1999 it was similar to soil loss from cowpea treatments and Pueraria-burned residue (2.3–5.3 Mg ha 1). There were no significant differences in soil loss in 1998 (1–3.2 Mg ha 1) whereas Mucuna-burned residue had a greater soil loss (28.6 Mg ha 1) than mulched cowpea (6.9 Mg ha 1) and Pueraria (5.4 Mg ha 1). Mound heights (23 cm average) decreased non-linearly with cumulative rainfall. A cumulative rainfall of 500 mm removed 0.3–2.3 cm of soil from mounds in 1997, 3.5–6.9 cm in 1998 and 2.3–4.6 cm in 1999, indicating that (detached but less transported) soil from mounds was far higher than observed soil loss in each year. Soil water retention was improved at potentials ranging from 1 to 1500 kPa by Mucuna-mulched residue compared to the various burned-residue treatments. Also, mound sorptivity at 1 cm water head (14.3 cm h 1/2) was higher than furrow sorptivity (8.5 cm h 1/2), indicating differences in hydraulic characteristics between mound and furrow. Pueraria-mulched residues for mounds had the highest sorptivity of 17.24 cm h 1/2, whereas the least value of 6.96 cm h 1/2 was observed in furrow of Mucuna-burned residue. Pueraria phaseoloides was considered the best option for soil conservation on the previously eroded soil, cultivated with mound tillage.

Salako, F.K., Kirchhof, G., Tian, G. (2000). Conservation of a tropical Alfisol using legume cover crop intercropping and residue mulch. Proceedings, "Tillage at the Threshold of the 21st Century: Looking Ahead", 5th Conference of the International Soil Tillage Research Organisation (ISTRO). Fort Worth, Texas, USA, 2-7 July 2000

Soil degradation is a major problem in west African land use environments. Although burning of crop residue is known to enhance soil degradation, it is still the most commonly used practice for land preparation. Intercropping with herbaceous legumes is a promising method to combat fertility decline and minimise resource degradation. A study was conducted from 1996 to 1999 in southwestern Nigeria to investigate the interaction of residue burning and legume intercropping on soil degradation as an improved and practical approach toward rehabilitating and conserving an Alfisol. Leguminous cover crops, [Mucuna pruriens (mucuna), and Pueraria phaseoloides (pueraria) with grain legumes [Vigna unguiculata (cowpea)] as control were intercropped with maize in 1996 and 1998; yam was cultivated in 1997 and 1999. Following local practices, mound tillage with hoe was adopted since 1997 for yam production. Subtreatments were burning and mulching of residues from the cover crops, cowpea and maize. Soil erosion and yam mound stability were used as sustainability indicators. The weighted annual mean erosivity was 6.5 103 MJ mm ha-1h-1 (EI30 index), 422 cm2 h-1 for the AIm index. Mean runoff amounts ranged from 20 to 32 mm in 1996, from 94 to 158 mm in 1997, and from 37 to 103 mm in 1998. Mean soil erosion ranged from 0.9 to 2.1 Mg ha-1 in 1996, from 3.8 to 7.8 Mg ha-1 in 1997, and from 1.8 to 3.7 Mg ha-1 in 1998. The burned residue plots had higher runoff and soil erosion than the unburned residue plots. Soil particles were eroded in proportions similar to plot particle size distribution. Mounding in 1997 accentuated soil erosion although transportation of detached soil by runoff was impeded by the mounds. Variations in mound heights were due to accretion as well as removal of soil from the furrows. There was no significant difference in soil erosion between the cover crops and cowpea. Yam mound erodibility (slumping) was largely determined by the length of exposure to rain in the 1998 cropping season. Mounds on the burned residue plot of each legume, except cowpea, slumped more than mounds on the unburned residue plot between April and August 1998 . The combined yields (1996-98) of maize, grain and yam tuber were higher in the unburned residue treatment compared to the burned residue treatment. Cover crop intercropping resulted in higher crop yield than the cowpea. We concluded that the Alfisol is best managed for sustainable crop production by no tillage, residue mulching and cover cropping. Residue burning should be avoided even if cover crops are used.

Tian, G., Kolawole G.O., Kang, B.T., Kirchhof, G. (2000). Nitrogen fertiliser replacement indexes of legume cover crops in the derived savanna of West Africa. Plant and Soil. 224(2): 287-296.

Legume cover crops are a potential means for overcoming N depletion in the derived savanna of West Africa. A 3-year trial was, therefore, conducted near Ibadan, southwestern Nigeria to measure the N contribution of 13 legume cover crops as compared to urea –N, using a N fertilizer replacement index for a maize test crop. Two series of trials involved the following legume cover crop species: Aeschynomene histrix, Centrosema brasilianum, Centrosema pascuorum, Chamaecrista rotundifolia, Cajanus cajan, Crotalaria verrucosa, Crotalaria ochroleuca, Lablab purpureus, Mucuna pruriens, Psophocarpus palustris, Pseudovigna argentea, Pueraria phaseoloides and Stylosanthes hamata. Trials were undertaken using a complete block design. Cover crops were planted in 1994 (Series 1) and 1995 (Series 2) in separate sites and each series was subsequently slashed and planted for one season with maize (Zea mays) in 1995 and 1996. At the 50% flowering stage, N concentration of above-ground vegetation of cover crops ranged from 21 to 38 g N kg??1. Nitrogen accumulated by 4.5-month old cover crops ranged from 14 to 240 kg N ha??1, depending on species and year. Cover crops increased grain yield of the subsequent maize crop by 25–136% over the control without N application. Nitrogen uptake by the maize crop was higher following cover crops than after maize or natural grass. The N fertilizer replacement index of cover crops for maize ranged from 11 (A. histrix) to 96 kg N ha??1 (C. cajan) in Series 2. Perennial (C. brasilianum, S. hamata, C. cajan, P. phaseoloides and C. verrucosa) and annual (C. rotundifolia, M. pruriens, C. ochroleuca and L. purpureus) species could potentially save 50 to 100 kg N ha??1 for maize crops. The cover crops accumulated more N in the wetter than in the drier year. However, the N fertilizer replacement index was higher for subsequent maize grown in the drier year. The cover crop-N recovery in maize was also higher than the urea-N uptake in the drier year. The N fertilizer replacement indexes can be predicted using the above-ground biomass amount of cover crops at 20 weeks after planting (drier year) or the N concentration at that stage (wetter year).

Salako, E. K., E. A. Olowokere, Tian, G., Kirchhof, G. Osiname, O. (2007). Ground cover by three crops cultivated on marginal lands in southwestern Nigeria and implications for soil erosion. Spanish Journal of Agricultural Research 5(4): 497-505.

Resource-poor farmers in developing nations cultivate marginal lands, thereby exacerbating the problem of soil degradation through poor plant growth and ground coverage. An assessment of ground cover under such a practice will provide a guideline for soil conservation. Ground cover by leguminous cover crops (e.g., Mucuna pruriens, Pueraria phaseoloides and Vigna unguiculata), associated with yam, maize and rice was measured in three different experiments in southwestern Nigeria using beaded-string method while leaf area was measured using a flat-bed scanner. The leaf area was used in obtaining equivalent of ground cover fraction from the leaf area index. Ground cover by yam was

D Hauswirth, Pham Thi Sen, O Nicetic, F Tivet, LQ Doanh, E Van de Fliert, G Kirchhof, S Boulakia, S Chabierski, O Husson, A Chabanne, J Boyer, P Autfray, P Lienhard, JC Legoupil, ML Stevens, 2012. Conservation agriculture and sustainable upland livelihoods innovations for, with and by farmers to adapt to local and global changes, 3rd International Conference on Conservation Agriculture in Southeast Asia. 10th - 15th December 2012, Hanoi (Vietnam)

Agriculture in whatever age, under whatever natural, economic and social conditions, has to feed the human being. To fulfil this mission, the sector has to overcome continuous and changing challenges to achieve notable developments. The Green Revolution, through developing and introducing high-yielding crop varieties and advanced crop management techniques, saved billions people from starvation. The advent of biotechnology, in its turn, has speed up the agricultural growth to meet food demands of the world's booming population. Continuous demographic pressure and rapid market integration have created necessity to further agricultural developments to meet not only food security, but also the increased demands for nutrition security, food safety, energy, etc., while the global climate change has created needs for capturing synergies between agricultural production and environmental protection. New breakthroughs to trigger the second Green Revolution have therefore become necessary. Thus, it is now the right time for us to consider the means to make "the Double-Green Revolution" to become a reality. Conservation Agriculture (CA) has demonstrated potential to meet this goal through designing and promoting the adoption of environment-sound and climate-resilient agricultural production systems. Increasing interests and efforts have been given to CA research for development in the Southeast Asia during the last 15 years.

Gunnar Kirchhof, Nguyen Hoang Phuong, Trinh Duy Nam, Oleg Nicetic, 2012. Farmer-friendly erosion control measures in maize-based systems of the northern mountainous region of Vietnam , 3rd International Conference on Conservation Agriculture in Southeast Asia. 10th - 15th December 2012, Hanoi (Vietnam)

We evaluated soil erosion rates in farmers’ field to assess when erosion occurs during the maize season and to identify which soil management aspects have the most profound impact on soil erosion reduction. We used a modified profile meter method to monitor erosion in farmers field (Hudson, 1993). Unlike Wischmeier plots, this method has minimum impact on farm operations. In short, this method monitors the drop in soil surface level below fixed reference point. These reference points are steel pegs (pins) inserted in the soil and distance between top of pin and soil surface measured following rainfall event. Our pin method comprised 4 soil pins inserted into the ground to ~40 cm in a 70x100 cm rectangle and we monitored soil surface to pin distance at 8 constant locations within this erosion station. Measurement errors using this method can be large due to slumping of soils after tillage and soil swelling. We compensated for these shortcomings by taking a large number of measurements, monitoring of soil bulk density to account for slumping of soil and assumed shrink-swell was negligible on these 1:1 type clay soils. Although slumping occurred, it happened very quickly after tillage following rainfall and once the maize was sown, slumping was no longer observed; i.e. there was no measurable change in surface bulk density after maize was sown. The research comprised of two phases: (i) collection of baseline date on erosion in farmers field and (ii) to monitor soil erosion in field experiments at two Communes, Na Ot (Son La) and La Nga (Moc Chau). The field trials (ii) was a complete randomized design using 4 blocks. Each plot had two erosion monitoring stations and erosion was measured 8 times during the maize season in Na Ot and 10 times in La Nga. Slopes were ~25º. Other key measurements were rainfall intensities, final maize yields, bulk densities and infiltration rates (i.e. single ring). Following discussion with farmers, treatments were adjusted to what farmers though they may use in future. Cultivation at both sites was done using a hand hoe. At La Nga the treatments were (i) cultivation residue retained plus additional mulch added, (ii) cultivation and residue retained, (iii) minimum cultivation with residue retained and (iv) cultivation with residue retained and rice-bean intercrop, i.e. all treatment had residue retained and no burning took place. The amount of residue from the past crop ranged from 1 to 3 t/ha, the additional residue applied ranged from 3 to 5 t/ha. At Na Ot the treatments were (i) slash and burn, (ii) residue retained and cultivation, (iii) residue retained and mini-terraces and (iv) residue retained and minimum cultivation; i.e. all treatment except treatment (i) had residue retained. Average residue amount left from the last season was 4.3 t/ha with an average groundcover of 83% before land preparation. The difference in residue amounts between the two sites is due to grazing during the dry season. For the benchmark study (phase i), erosion was monitored in farmer fields of 5 villages from End-July to mid-October at 5 different times. These villages were located in different communes in 4 provinces (Mai S?n, Moc Chau, Sin Ho, Tam ???ng). Erosion stations were located within farmers’ fields on slopes between 20º and 30º on slope lengths larger than 100 m. Distribution of the 68 erosion station was uneven between farmers’ fields as it depended on access and farmer support to allow measurement. Average soil loss ranged from 8 to 15 t/ha during that time and there were no significant differences between provinces, communes and farmer fields. We attributed these low erosion rates due the late onset of the monitoring schedule; i.e. maize was well established providing effective erosion protection through reducing raindrop impact. Given obvious visual assessment of erosion, we concluded that most erosion occurs during the early phase of the growing season while the soil is unprotected. During the 2011 maize season average erosion at La Nga was 38 t/ha, with a very large variation from 3 to 95 t/ha, but no significant differences between treatment and it was not possible to differentiate between erosion rates at the start and towards the end of the maize season. We attributed the lack of significant differences to the similarity of treatments where all treatments had residue retained as well as the inherent variability of the erosion method we used. At Na Ot total erosion rates were much higher compared to La Nga and segmental regression of erosion rates showed that there was a significant difference between the start and the end of the maize season. Most erosion occurred until the 7 July 2011 (initial soil loss). The first erosion measurement was done on the 22 April and maize sown on the 11 May. This suggests that a large proportion of soil lost during the initial phase occurs after land preparation and before the maize is planted and aggravated by weeding (Podwojewski et al. 2008). Initial soil loss was 226 t/ha for treatment (i), i.e. slashes and burn. There were no significant differences between the other treatments where residue was maintained and average initial soil loss was 101 t/ha. The difference between residue burnt and residue maintained was significant at the 5% level. The average soil loss rates after the 7 July 2011 was 17 t/ha with a range of 5 – 25 t/ha and no significant differences between treatments. The results of our research showed that most soil erosion occurs within the first 2 months of the cropping season and the main factor in reducing erosion is maintaining ground cover. The importance of this finding is that practice to reduce erosion is to encourage farmers not to burn and to maintain crop residue.

Neal Menzies, Andrew Verrell, Gunnar Kirchhof, 2012, Keynote 5: Can conservation farming practices ensure agricultural ecosystem stability?, 3rd International Conference on Conservation Agriculture in Southeast Asia. 10th - 15th December 2012, Hanoi (Vietnam)

Conservation Agriculture is deemed to be the only sustainable form of agricultural production system. Adoption rates in the Americas and Australia have been extremely high associated with increased and more efficient crop production, but primarily due to the reduction of herbicide cost, mainly Glyphosate, after patents expired and competition for production increased, lowering the cost of Glyphosate. Conservation agriculture is a production system where a key component isherbicide use to replace tillage in the control of weeds. Other equally important components are mechanisation, and residue retention; associated with crop rotation to reduce the likelihood of pest and disease outbreaks. Practitioners of conservation agriculture universally understand that that all components must be applied; partial adoption of the conservation agriculture principles will not be sustainable. In regions where conservation agriculture has been adopted as a system, at present, it is the best management practise for agricultural ecosystem sustainability. However, in many developing countries, practise change for all components of conservation agriculture may not be possible. Herbicide availability and cost is probably a major limiting factor; in particular, in many sub-Saharan counties. The need for agricultural mechanisation at present still limits the adoption in many African and Asian countries. Crop rotation may not fit into traditional production systems and minimum tillage is not possible to implement for root or tuber crops. Similarly, genetically modified cotton production requires tillage for pest control. Soil and climate interactions may also hinder adoption of the minimum tillage component. Some soils, for example heavy self-mulching Vertisols respond very well to the conversion from conventional to zero-tillage and benefits in terms of increased water use efficiency are evident shortly after aggressive tillage operations ended. However, less active soils, in particular hardsetting soils, may not respond rapidly to zero tillage, and it may take several years of zero-tillage practise before soil structure has sufficiently improved for conservation farming to outperform conventional practices. In Australia, profound nutrient stratification (accumulation in the surface soil) also presents a challenge to zero tillage. At present is seems that conservation agriculture is promoted as a ‘must adopt’ as a system where, at present, this may clearly not be possible in some biophysical/socio-economic environments. The change to conservation agriculture needs to be stepwise process where adoptable components are promoted and associated limitations are addressed without short term yield sacrifice. Key indicators for the agro-ecosystem stability of conservation agriculture are soil organic matter build-up and carbon sequestration due to minimum soil disturbance and residue retention and increased water use efficiency. Increases in the soil organic carbon stocks are largely reported on conservation agriculture fields in the Americas. Research in Brazil suggests that organic matter build-up under conservation agriculture can even be greater than under natural ecosystems. Results from the USA suggest that soil organic matter build-up is a major mechanisation for carbon sequestration. On Vertisols in Australia adoption of conservation farming was partly due to the realisation that carbon stock depletion needs to be arrested, and the belief that soil organic matter can be increased in conservation agriculture systems. However, despite soil structural improvement due to adoption of zero-tillage systems, recent data from longditudinal studies shows that carbon stocks have continued to decrease under conservation tillage, though at a lower rate than observed in conventional tillage. For example, on farmers field were conservation agriculture has been practised for over two decades, no increase in soil organic carbon was measured. Unless annual rainfall is above 500 mm, increase in soil organic matter as a consequence of conservation farming practises appear to be negligible. If these values also apply to soils and climates in Africa, large regions of Africa need to be excluded as potential carbon sinks. Minimum tillage systems, once soil structure has improved, even in the absence of organic matter increases, will have increased water use efficiency. This is primarily due to the greater amount of actual available water but not necessarily due to an increase in potential plan available water. The main mechanism for high amounts of plant available water in the soil profile and associated higher water use efficiencies is greater infiltration rates that allow the soil profile to fill out with water. Benefits for crops are obvious but there may be a hidden cost for environmental flows. Higher water use efficiency is synonymous to lower losses in the water balance may well lead to reduced water availability downstream from regions were conservation agriculture is practises. The potential impact on landscape hydrology are largely unknown.

Kirchhof G, So HB, Tuong TP (2011). Puddling: Effect on Soil Physical Properties and Crops. In: Encyclopedia of Agrophysics, Springer Reference, Gli?ski, Jan; Horabik, Józef; Lipiec, Jerzy (Eds.). 1st Edition., 2011, p667-8.

Soil puddling for paddy rice production is the process of working saturated or near-saturated soil into soft structureless mud. Tillage in lowland rice production systems (paddy rice) is synonymous with puddling. Puddling is achieved by cultivating the soil under saturated condition using animal drawn or tractor driven implements. Mechanical breaking and dispersing of soil aggregates destroys the soil structure and forms the puddled zone. Puddling softens the soil and assists manual transplantation of rice seedling, minimizes water use through reduced percolation losses and effective weed control. Over time, soil puddling also creates a compacted layer below the puddled zone which further reduces percolation losses. The least permeable zone is usually found just below the puddled layer where tillage implements created a thin smeared layer. The reduction in permeability is mainly caused by blocking of macropores with fine dispersed particles translocated during puddling process, and the smearing effect of the tillage implements. Although lowland rice does not require saturated conditions to produce high yields, it is traditionally kept under submerged conditions to maximize water supply, mobilize nutrients, and to control weeds, which is generally not possible without puddling. However, preferential flow or bypass flow through macropores, cracks, or large biopores contributes to water losses in paddy systems. This includes water losses though bunds which are not puddled. Water moves laterally into the bunds and then percolates down through the under-bund areas that are not puddled. Despite the benefits of puddling for rice production, there are adverse effects, especially on post-rice crop production. Due to its structureless nature, puddled soils tends to harden and crack upon drying, with the rate and size of crack development depending on the rate of drying, type of clay, and clay content. These characteristics are the main constraint to the establishment and growth of post-rice crops. Irrigation of dried paddy soils can result in excessive losses from bypass flow, while severe cracking can result in root breakage and excessive strength impedes root growth. Although soil puddling reduces the percolation rates, the puddling process itself requires large amounts of water. With increasing water scarcity, alternative tillage methods to reduce water use are needed. Dry tillage prior to flooding can reduce water requirements substantially by filling cracks and disrupting bypass flow pathways. It has become apparent that soils have often been puddled excessively. On clay soils, sufficient reduction in hydraulic conductivities can be achieved with only one pass of the puddling implement, but coarser textured soils may require several passes. Landscapes with very shallow water tables may not need puddling at all, while broad cast planting of pre-germinated seed can save labor without sacrificing yield. In the context of rice and upland crop rotations, minimizing puddling to reduce soil structural degradation will benefit post-rice crops such as legumes or wheat.

Radrizzani AB, Shelton HM, Dalzell AC, Kirchhof G (2011). Soil organic carbon and total nitrogen under Leucaena leucocephala pastures in QueenslandCrop & Pasture Science, 2011, 62, 337–345.

Soil organic carbon (OC) and total nitrogen (TN) accumulation in the top 0–0.15m of leucaena–grass pastures were compared with native pastures and with continuously cropped land. OC and TN levels were highest under long-term leucaena–grass pasture (P 20 years old had negative GHG balances; lower additional topsoil OC accumulation rates compared with native grass pastures failed to offset animal emissions.

Liu Y, Sabboh H, Kirchhof G, Sopade P (2010). In vitro starch digestion and potassium release in sweet potato from Papua New Guinea. International Journal of Food Science and Technology 2010, 45, 1925–1931.

Twenty samples of sweet potato from Papua New Guinea, made up of cultivars 3-mun, Carot kaukau, Wahgi besta, Nillgai, Baiyer kaukau, and 1-mun from three provinces, three farmers, and three locations, were subjected to an in vitro starch digestion procedure. Digestion of starch was studied by glucometry, while potassium release was monitored using electrochemistry. The potassium content of the nondigested samples ranged from 4 to 17 mg g)1 dry solids, while the starch content was from 47 to 80 g per 100 g dry solids and independent of G · E effects. In vitro starch digestibility (2–75 g digested starch per 100 g dry starch) significantly (P

Bah R.A, Kravchuk O., Kirchhof G. (2009). Fitting Performance of Particle-size Distribution Models on Data Derived by Conventional and Laser Diffraction Techniques. Soil Science Society America Journal. 73, 1101-1107

Mathematical description of most classical particle size distribution (PSD) data is often used for estimating soil hydraulic properties. Fast laser diffraction (LD) techniques now provide more detailed PSDs, but deriving a function to characterize the entire range of sizes is a major challenge. The aim of this study was to compare the fitting performance of seven PSD functions with one to four parameters on sieve-pipette and LD data sets of fine-textured soils. The fits were evaluated by the adjusted R2, MSE, and Akaike’s information criterion. The fractal and exponential functions performed poorly while the performance of the Gompertz model increased with clay content for the LD data sets. The Fredlund function provided very good fits with sieve-pipette PSDs but not the corresponding LD data sets, probably due to underestimation of the clay fraction in the latter. The two-parameter lognormal function showed better overall performance and provided very good fits with both sieve-pipette and LD data sets.

Bah R.A., Karvchuk O, Kirchhof G. (2009). Sensitivity of drainage to rainfall, vegetation and soil characteristics. Computers and Electronics in Agriculture, Volume 68, Issue 1, August 2009, Pages 1-8.

Rainfall, vegetation characteristics and soil hydraulic properties influence deep drainage patterns in agricultural landscapes, but more information is required on the variability of their interactions with site conditions. Therefore, the objective of the study was to investigate the impact of the interactions of soil permeability, vegetation rooting depth and growth duration on drainage in 3 sites in northern New South Wales, Australia. Local sensitivity analysis was used on drainage estimated by two biophysical models—WaterMod 3, with a crop growth module, and HYDRUS-1D without a crop growth module. The effect of saturated hydraulic conductivity (Ks), growth duration (GD), rooting depth (RD), annual rainfall, and their interactions on deep drainage was evaluated at 3 sites. Simulations were conducted using 30 years of randomly selected climate data from 115 years historical data. Rainfall variability was similar in all 3 sites, so annual rainfall was the dominant factor dictating drainage in all 30 rainfall years whereas GD was more important than RD after accounting for rainfall and drainage was least sensitive to Ks. The minor impact of RD was ascribed to the soil water content being at the lower extraction limit of crops due to potential evaporation being greater than rainfall in almost all months of the rainfall-year. The importance of GD varied between rainfall-years and sites, and was generally higher at high annual rainfall. We conclude that the level of precision at which model inputs are defined would vary with annual rainfall level. Therefore, GD could be defined on a rough scale in low rainfall zones, whereas more precise definitions are necessary at high rainfall. This would depend on classification of rainfall zones based on reliable rainfall data.

Junge, Deji, Abaidoo, Chikoye, Stahr, Kirchhof, OVERVIEW ABOUT SOIL CONSERVATION TECHNOLOGIES AND THEIR PERCEPTION BY FARMERS IN NIGERIA, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof, p49-59. (http://www.aciar.gov.au/publication/TR71)

In Nigeria, West Africa, soil degradation has been one of the most critical environmental problems for a long time. Hence, there has been and still is an urgent need to develop effective soil resource management systems that can reverse the trend. Sustaining soil productivity will enhance food security and alleviate poverty. An extensive literature search that started in 2006 has shown that soil conservation has a long tradition, and earlier and present initiatives have resulted in various on-farm and off-farm technologies. As these have rarely been evaluated to establish adoption rates, an assessment study was performed in 2007 to analyse the effectiveness and adoption of past and present soil conservation initiatives. Villages with different types of conservation technologies were visited and farmers in south-west Nigeria were interviewed to obtain information on their experiences. Mulching, cover cropping and contour tillage are likely to be effective on-farm soil conservation measures practised in Nigeria. They are generally adopted by farmers as they are compatible with the existing farming system, and cheap and easy to install and maintain. Education, knowledge on soil conservation, labour availability and membership in organisations have a positive influence on the adoption rate of technologies.

Kirchhof G, (2009) Editor, Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, ACIAR Technical Reports 71, 126p (http://www.aciar.gov.au/publication/TR71)

High population growth is a problem in most developing countries. Projections for many countries are that the increased demand for food will outstrip the capacity of the land to produce that food. In Papua New Guinea (PNG) the population has doubled since 1966 and the current growth rate is around 2.7%. Despite this high growth rate, the area under agricultural production has remained stable, but land use has intensified. Fallow periods have decreased from several decades to less than one decade. This trend towards more continuous cropping systems is linked to high population densities—as the population increases, the demand for food and cash crops increases. Thus, the need to identify promising management practices to expand both food and cash crops, while sustaining soil fertility, is becoming increasingly important for PNG. This problem is not new: nor is it unique to PNG. Theoretical solutions to the problem of increasing crop productivity while sustaining soil productivity exist, but often they are not applicable to the local agroecological and socioeconomic conditions. For example, use of mineral fertiliser could easily offset production constraints due to depletion of nutrients as a result of continuous cropping, but fertiliser is not accessible for most resource-poor farmers in PNG. Therefore, novel integrated soil-, crop-, nutrient- and water-management practices best suited to local conditions should be developed, pilot tested and transferred to the farmers. Prior to engaging in research to improve or overcome soil constraints, it is imperative to understand current land management systems and the socioeconomic drivers behind these systems. Surveys of farmers play an important role in understanding their current practices and identifying the main constraints to increasing crop productivity. Such information is beneficial in the investigation of management practices that optimise the integrated use of all locally available nutrient sources for sustainable crop production, but have minimal adverse effects on the environment. This report summarises the results from a pilot study on soil fertility management funded by the Australian Centre for International Agricultural Research (ACIAR), and reviews sweetpotato-based cropping systems in the highlands of PNG. It also describes the lessons learnt from survey methodologies used to assess the socioeconomic and biophysical constraints to sweetpotato production in this area. Case studies from similar surveys done in Nigeria and northern New South Wales, Australia, are included as examples.

Kirchhof, Daniells, CHANGING TILLAGE MANAGEMENT PRACTICES AND THEIR IMPACT ON SOIL STRUCTURE PROPERTIES IN NORTH WESTERN NEW SOUTH WALES, AUSTRALIA, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof p60-69. (http://www.aciar.gov.au/publication/TR71)

A study was conducted in 1998 in north-western New South Wales to assess how changes in tillage practices and farmers’ perceptions of ‘good’ or bad’ paddocks relate to soil structural properties. Forty landholders were visited and interviewed to obtain background information on their current and past management practices, crops and cropping systems used, and what they expect in the future. The majority of the soils were Vertosols (78%), with some Kandosols and a few Chromosols. Conventional tillage was practised on 63% of the fields surveyed. Conservation tillage (minimum or zero-tillage) was only practised on swelling clay soils. On these soils 26% of the fields had been converted from conventional to conservation tillage during the past 3 years, while on 14% of the fields conservation tillage had been practised since they were brought into crop production (3–10 years previously). Saturated hydraulic conductivities on the farmed black Vertosols with a history of conventional tillage were lower than those of the virgin sites, but increased after conversion from conventional to conservation tillage. Fields that were brought into cropping during the last 10 years using conservation tillage only had higher saturated conductivities than the virgin sites. There was little effect of cropping history on saturated hydraulic conductivity on the grey Vertosols. Soil organic carbon on the control sites was always greater than on the corresponding cultivated sites, regardless of whether conventional or conservation tillage was practised. Tillage history did not affect any of the measured soil chemical properties. Platyness of soil structure was a clear indicator for wheel-induced compaction. Platy structure was not shown on any of the swelling clay soils at the never-cultivated sites, and tended to be more frequent on the ‘poor’ sites. This was most pronounced for the grey Vertosols, where 80% of the ‘poor’ and 50% of the ‘good’ sites were platy, and on the black Vertosols, with 42% and 31% respectively. The overall close agreement between platyness and the farmers’ perceptions of ‘good’ and ‘poor’ sites indicated that platyness has an impact on soil productivity and that soil compaction continues to be a limiting factor for crop production. We also concluded that black Vertosols respond better to conservation tillage than grey Vertosols, possibly due to their greater resilience and better ability to self-ameliorate. The absence of conservation tillage adoption on non-swelling clay soils in this region (at the time of the study) may reflect the length of time required before conservation tillage improves soil structure and, ultimately, yield.

Kirchhof, Taraken, Ramakrishna, Ratsch, Igua, BIOPHYISCAL CONSTRAINTS OF SWEET POTATO BASED CROPPING SYSTEMS IN THE PNG HIGHLANDS, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof p95-109. (http://www.aciar.gov.au/publication/TR71)

Population growth in the Paua New Guinea highlands is among the highest in developing countries. While the 2000 census reported a rate of 3%, more realistic estimates may be closer to 2%. Even if exact rates are unknown, the trend of expanding population will continue and could result in a doubling of the population to around 4 million in just over 3.5 decades. This will place unprecedented pressure on the land resource. However, it is still unclear if the resource-base ‘soil’ is indeed being depleted at a greater rate than it can be restored, given the potentially high productivity of the soils in the region. We surveyed farmers and assessed their gardens to evaluate if soil fertility and associated production of the most important staple food, sweetpotato, is indeed declining as a consequence of increasing land pressure, shortening fallow periods and a number of other factors, including pests and diseases. This survey included 95 farmers in four highlands provinces with an average of three districts in each province. Farmers’ perceptions on soil fertility decline and management options were obtained. They were then asked to show us one garden that had recently been brought back into production after fallow, the ‘new’ fertile garden, and another garden that was about to go into fallow, the ‘old’ run-down garden. Plant and soil samples were collected from these two gardens to quantify changes as a result of cropping over time.

Kirchhof, Taraken, Ratsch, Kapal, Igua, SURVEY METHODOLOGY TO ASSESS SOCIO-ECONOMIC AND BIOPHYSICAL CONSTRAINTS – LESSONS LEARNT IN THE PNG HIGHLANDS, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof p70-78. (http://www.aciar.gov.au/publication/TR71)

Among developing countries, Papua New Guinea (PNG) has one of the highest population growth rates. As land under cultivation has been stable for decades, the increasing demand for food is placing unprecedented pressure on the land resource under agriculture. An exploratory farmer survey in the highlands of PNG was conducted to assess farming practices in relation to soil productivity decline over time as population increases. The survey comprised farmer interviews as well as the collection of a biophysical dataset, including soil and plant analyses, to underpin farmer perceptions of a potential problem regarding soil fertility. Unlike most farmer surveys, this survey combines socioeconomic data with biophysical measurements. This type of exploratory survey was considered to be necessary to delineate the need for further research intervention. The baseline dataset is also useful to measure post-project impact and adoption, which is often inferred from auxiliary data if baseline data are missing. A main deficiency of the exploratory survey was bias in sample location caused by village access problems and safety concerns. The willingness of farmers, male or female, to participate in the interviews, and sample collection for the biophysical assessment of their gardens, were not problems.

Kravchuk , Wilson, Kirchhof, Statistical methods for a soil fertility management survey analysis in Papua New Guinea, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof p79-87. (http://www.aciar.gov.au/publication/TR71)

This paper is a short communication about methods used in the analysis of biophysical data from the scoping stage of a soil fertility management survey in Papua New Guinea conducted in September–October 2005 (Australian Centre for International Agricultural Research project SMCN/2005/043). The goal of this communication is to describe and promote the good practice of statistics in application to biophysical surveys. A step-by-step analysis is presented of the difference in sweetpotato yield between newly established gardens and gardens that have been cultivated for a long period. We comment on the strengths and limitations of statistical techniques used in the analysis, and also relate the techniques to the corresponding software procedures (R15, Minitab Inc., Chicago). Although we refer to various general methods, the analysis presented is specific to one particular survey. This paper may be useful for agricultural researchers as a case study of the data analysis of field surveys in research or extension projects.

Liu Y, Sabboh H, Kirchhof G, Sopade PA. (2009). Digestibility of starch and potassium in sweetpotato from Papua New Guinea. Proceedings, 15th Triennial Symposium of the International Society for Tropical Root Crops, 2-6 November 2009, International Potato Centre, Lima, Peru.

Potassium is a major mineral in sweetpotato, and like most root crops, sweetpotato has high starch content. There are many cultivars of sweetpotato with genotype and environmental differences, which influence digestibility and bioavailability. Starch and mineral digestibility in food materials are currently topical because of associated nutritional implications. Time-course in-vitro starch and potassium digestibility of 20 samples of sweetpotato from Papua New Guinea were studied using glucometry and electrochemistry/spectroscopy respectively. The samples were made up of six cultivars (3-mun, Carot kaukau, Wahgi besta, Nillgai, Baiyer kaukau, and 1-mun) planted in three provinces by three farmers in three different locations. The potassium content of the non-digested samples ranged from 4 – 17 mg/g dry solids, while the starch content was from 47 – 80 g per 100g dry solids and essentially independent of cultivars, farmers and locations. In-vitro starch digestibility (2 – 75 g digested starch per 100g dry starch) significantly (p

Ramakrishna, A., Bailey, J.S. & Kirchhof, G. (2009). A preliminary diagnosis and recommendation integrated system (DRIS) model for diagnosing the nutrient status of sweet potato (Ipomoea batatas). Plant and Soil. 316, 107-116.

Critical leaf nutrient concentrations have often been used to diagnose the nutritional causes of crop underperformance. Unfortunately, these diagnostic criteria are not available for mature, tuber-bearing sweet potato plants (the word ‘tuber’ being used to describe a swollen root rather than a swollen stem). The Diagnosis and Recommendation Integrated System (DRIS), however, provides a reliable means of linking leaf nutrient concentrations to the yield of sweet potato tubers, and may be developed for this crop using existing data from regional crop surveys. In the present study, tuber yield and leaf nutrient concentration data from a survey of sweet potato gardens conducted in the Papua New Guinea (PNG) highlands in 2005 were used to establish DRIS N, P, K, and S norms and statistical parameters for sweet potato. Although the database was relatively small, the norms derived for nutrient ratios of key biological significance, i.e. N/S and K/N, were within the expected narrow ranges for higher plants, giving credibility to both the database and the DRIS model. Data from future surveys and field trials may subsequently be used to enlarge the database allowing the refinement of model parameters and hopefully an expansion of diagnostic scope to include other macro and micro-nutrients. As it stands, though, this preliminary DRIS model for sweet potato is possibly the best diagnostic tool currently available for evaluating the N, P, K and S statuses of sweet potato crops in the pacific region.

Wegener, Kirchhof, Wilson, SOCIO-ECONOMIC ANALYSIS OF VILLAGE GARDEN MANAGEMENT IN THE PNG HIGHLANDS, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof p88-94. (http://www.aciar.gov.au/publication/TR71)

A survey of approximately 100 village gardeners in the Papua New Guinea (PNG) highlands was conducted in 2005 as a preliminary step in setting up an Australian Centre for International Agricultural Research project to improve the nutrition of sweetpotato in the highlands. Sweetpotato is the main staple crop in the PNG highlands, which had a population of around 2 million (or 40% of the country’s population) at the 2000 census, with around 2–3% annual growth. Despite these high growth rates, the area under agricultural production has remained fairly static, resulting in increasing pressure on land resources. Farmers are concerned about yield decline, as sweetpotato yields from fallowed land, or land recently brought back into production as part of the recycling of gardens that occurs in the highlands, tend to be much higher (2–8 t/ha tubers) than yields from old gardens. Despite high apparent nutrient stocks and favourable carbon:nitrogen ratios in the soil, most sweetpotato tissue samples have shown low nutrient levels, in particular of nitrogen, phosphorus, potassium and boron. The survey was conducted to assemble background information on farm locations, farm practices, crop yields, and soil and plant analysis. The conceptual framework proposed to guide the analysis was that background factors (such as location, garden type, land availability, age and sex of farmer, number of children in household and sources of other income) affect management practices. These management practices (soil preparation, planting system, fertility management including fallowing, use of animals such as goats and pigs in the farming system, and crop rotations) influence outcomes such as plant and soil analyses; sweetpotato yields; plant symptoms; tuber characteristics such as weight, size, colour and cracking; presence of nematodes; and ability to grow other crops. A preliminary analysis of the survey data has been conducted and results are reported in this paper.

Bailey, J.S., Ramakrishna A. & Kirchhof, G. (2008). Relationships between important soil variables in moderately acidic (pH = 5.5) soils in the highlands of Papua New Guinea and management implications for subsistence farmers. Soil Use and Management. 24, 281-291.

The fertility of farmed soils in parts of the Papua New Guinea (PNG) highlands reputedly has been declining for some time owing to population pressure. To assess the extent of the problem, a survey of sweet potato gardens was conducted across four of the highlands provinces and information on soil variables was obtained for gardens on soils of volcanic and non-volcanic origins. In the absence of fertilizer application, soil fertility in the humid tropics is largely a function of soil cation exchange capacity (CEC), and soils of low CEC had previously been reported in this region. In the present study, relationships between effective CEC (ECEC) and other soil properties in moderately acidic soils (pH 5.5–6.3) were investigated to see if there was scope for improving soil cation retention characteristics through management of key soil variables. For volcanic soils of varying allophane content, ECEC was, unexpectedly, negatively correlated with soil C and soil C/ N, most probably because of the formation of humus–allophane complexes which had facilitated organic matter accumulation whilst dramatically reducing the free negative charges on the material. Given the latter outcome, the indigenous practice of heaping compost in the centre of soil mounds appeared to be one of the best strategies for circumventing the problem of low CEC, as nutrients in the compost are held in an environment virtually independent of the surrounding soil mineralogy. Although the positive correlation between soil pH and soil ECEC was weak for volcanic soils, it was concluded that liming might nevertheless be an effective means of enhancing the nutrient retention characteristics of these soils provided the practicalities and costs were not prohibitive.

Bailey, J.S., Ramakrishna, A. & Kirchhof, G. (2008). An evaluation of nutritional constraints on sweet potato (Ipomoea batatas) production in the central highlands of Papua New Guinea. Plant and Soil. 316, 97-105.

Sweet potato (Ipomoea batatas) is the staple food crop in the highlands of Papua New Guinea (PNG). Declining crop productivity, however, appears to be threatening the sustainability of sweet potato-based farming systems within the region, a probable cause being the exhaustion of soil nutrient reserves in continuously cultivated sweet potato gardens. To assess the extent of the problem, a survey of sweet potato gardens was conducted across four of the highlands provinces and information on soil and crop variables was obtained for old gardens (cultivated over many seasons) and new gardens (newly brought into cultivation) on soils of volcanic and non-volcanic origin. Crop leaf nutrient data collected in the survey were interpreted using the Diagnosis and Recommendation Integrated System (DRIS), to try to identify the main nutritional constraints on tuber production in different garden types on soils of volcanic or non-nonvolcanic origin. The results suggested that K deficiency was the primary cause of poor crop production in almost a third of sweet potato gardens, but was more of a problem in old gardens than in new. Phosphorus deficiency was also a problem on volcanic soils, and S deficiency on non-volcanic soils. These latter deficiencies, however, were at least as prevalent in new gardens as in old. Important factors contributing to K and S depletion from garden systems were the removal of K and S-rich vines from cultivation areas, the shortening of fallow periods and the burning of weed and crop residues, the latter releasing S (SO2) to the atmosphere. Correction of K and S deficiencies may require the recycling of old vines back to sweet potato cultivation areas and the adoption of a zero-burn policy for fallow management. Correction of P deficiency may necessitate the use of P-accumulating fallow species, e.g. wild Mexican sunflower (Tithonia diversifolia), to extract the P fixed by sesquioxide and allophanic minerals.

Beal CD, Rassam DW, Gardner EA, Kirchhof G, Menzies NW. (2008). Influence of Hydraulic Loading and Effluent Flux on Surface Surcharging in Soil Absorption Systems. Journal of Hydrologic Engineering. 13:8, 681-692.

The goal of this study was to investigate how extreme hydraulic loading influences hydraulic pathways, and thus failure potential, of two soil absorption systems. A grid of tensiometers and piezometers were installed beneath and adjacent to the absorption trenches, and water height was manipulated to simulate different hydraulic loadings. At both sites, measured soil matric potentials along the trench sidewalls increased toward zero as water height increased over time, indicating that water was preferentially flowing laterally above the biomat zones. Saturated hydraulic conductivity Ks of the soil and biomat, and other hydraulic parameters were calibrated using inverse modeling procedures in HYDRUS-2D. We found generally good agreement between measured and predicted matric potentials. The calibrated model was then used to predict fluxes through different infiltrative zones under typical and extreme hydraulic loads. Modeling indicated that the overall infiltration rates through the biomat and subbiomat zones fell within a relatively narrow range of 0.025–0.046 m/day at the two sites. Under extreme hydraulic loading to trenches, fluxes through the upper trench sidewalls i.e., the exfiltration zone were predicted to be substantially greater i.e., 80% of total flux than through the biomat zone. This confirms the conclusions made from field results, that a permeable exfiltration zone provides a critical buffer to surface surcharging during extreme trench loading. Conversely, the presence of a high sidewall biomat can reduce sidewall exfiltration of effluent, and therefore increase the likelihood of surface surcharging.

Kirchhof G, Ramakrishna A (2008). Analysis of biophysical and socio-economic constraints to soil fertility management in the PNG Highlands. Final report – ACIAR project SMCN 2005/043. 37p. http://www.aciar.gov.au/project/SMCN/2005/043

Project Background and Objectives In Papua New Guinea's highlands, soils are rich and productive. Both crop production and agroforestry are widely practiced. The most extensively grown crop is sweet potato, the main food staple, cultivated on between 50 and 90 per cent of arable land. Recent declines in sweet potato yield suggest soil fertility is also declining. Pests and diseases may play a role, as may the shortening of fallow periods to cater for increased cropping to feed a growing population. Understanding the factors contributing to soil fertility and sweet potato yield decline is needed to guide future R&D activities. Information to build this understanding was collected to determine these factors, including the socio-economics of farmer decision-making. Project Outcomes The project team surveyed farmers and assessed their gardens to evaluate if soil fertility and associated production of the most important staple, sweet potato, was indeed declining as a consequence of increasing land pressure, shortening fallow periods and a number of other factors including pests and diseases. This survey included 95 farmers in four Highland provinces with an average of three villages in each province. Farmer's perceptions on soil fertility decline and management options were obtained. They were then asked to show the team one garden which had recently been brought back into production after fallow, the 'new' fertile garden, and another garden which was about to go into fallow, the 'old' run-down garden. Plant and soil samples were collected from these two gardens to quantify changes as a result of cropping over time. Sweet potato yields Sweet potatoes are harvested sequentially, making it notoriously difficult to obtain reliable yield data. The team used single harvest yields to assess relative production from this 'one-off' farmer survey. In both gardens, old and new, single harvest yields of up to 30 t/ha were observed with a median yield of 6 t/ha. Due to the sequential harvesting these yields were considerably lower than the average total yields of 13-15t/ha for lowland and highland systems reported by Bourke and Vlassak (2004). The large variation in the measured yields and cultivars prevented the use of covariates such as number of previous harvests and age of sweet potato plant to estimate total yields. However the team's observations were similar to others (2006) from an EU funded project on early maturing sweet potato varieties in the lowlands executed by NARI. Likely causes for the low yields were nutrient deficiencies, pests and diseases and presence of viruses in the sweet potato planting material (traditional and improved). Nutrient deficiencies were evident even though the predominantly volcanic ash soils in the Highlands are regarded as very fertile soils. In a 1997 study more than 50% of sweet potato tissue samples collected were deficient in N, P, K, S and B. Unclean planting material is also a major contributing factor to low yield, but it is unclear if pathogen-tested varieties would suffer nutrient deficiencies comparable to traditional varieties. Yield trends in old and new gardens Pests and diseases: The cause for low yields in old gardens? There was no difference in the degree of insect infestation of tubers between the old and new gardens (p=13%). There was also no significant difference in the expected percentage of cracked tubers between the old and new gardens (p-value > 7%). But the average yield of vines with cracked tubers was higher in the new gardens, indicating that new gardens produce higher yields even though tubers may have cracks. Despite higher yields, the new gardens tended to have larger counts of nematodes (p=5%), suggesting that the nematodes could be either non-parasitic or infestation is not a critical factor driving yield. The distribution of weevils was significantly different between the old and new gardens. The chances of the presence of weevils or larvae are significantly higher in the old garden (p-value 2200m) showed that high altitudes have considerably higher total N and soil organic carbon (SOC) than the lower. Despite these subtle differences in apparent soil fertility they had no impact on sweet potato yield. This is of particular interest because SOC is often regarded as an important indicator for soil health and fertility. Farmers perception The farmer's response to the survey was a strong willingness to cooperate. Farmers related yield reduction to soil fertility decline and were eager to collaborate as partners and requested feedback from our work. Their observation was that yields in older gardens are lower than in newer gardens and they blamed poor soil conditions for this decline. We asked farmers whether they could grow corn or common bean as a control question to assess their ability to judge soil fertility. The responses to both questions were closely related and farmers thought that the new gardens were more suitable for growing corn or common bean than the old gardens (corn p=4%, bean p=8%). However, the farmer's soil fertility assessment was not related to the sweet potato yields we observed, but it supported the argument that soil fertility differences exist between old and new garden. Soil fertility management and planting systems Yields in the new gardens were not affected by planting systems, but yields in the old gardens were highest if farmers used large mounds. In both, old and new gardens, mounds more than 70 cm high were associated with fertility management such as composting and short fallow (in old gardens). The high mounds system was mostly associated with high altitude. However, the difference in planting systems does not explain all the effect of altitude (p

Kirchhof G, Ramakrishna A (2008). Soil fertility assessment of soils in the highlands of Papua New Guinea. Paper. Soils2008 Conference – Soil, the living skin of planet Earth. Palmerston North, New Zealand, 1 – 5 Dec 2008. http://www.soilsconference.co.nz/page.php?17

The population in PNG highlands has increased on an average at 2.8% during 1980-2000 (National Statistical Office, 2002) and is amongst the highest in developing countries. The trend is likely to continue in the near future and could reach 4 million by 2020. Despite high population growth, the arable land for agricultural production has remained relatively stagnant (Bourke 1997, 2001) with concomitant intensification of land use and reduced fallow periods. Most agriculture systems in Papua New Guinea are variations of shifting cultivation systems, usually between 15 and 25 years long, compared to one to two years of cultivation. However, population pressure has resulted in reduction in fallow periods from several decades to less than one decade (Sam, 1996). In the long term, one can anticipate further shortening of fallow periods and lengthening of cropping cycles. There are already indications that soil fertility run-down is impacting on the productivity of the main staple in the area, sweet potatoes, which accounts for 55 to 90% of land under arable agriculture. However, at this stage it is still unclear wether the resource base ‘soil’ is indeed being depleted at a greater rate than it can be restored given the potentially high productivity of the soils in the region.

Kirchhof, G, Ramakrishna, A, & Bailey J.S. (2008). An evaluation of Colwell-P as a measure of plant available phosphorus in soils of volcanic and non-volcanic origin in the highlands of Papua New Guinea. Soil Use and Management. 24, 331-336.

Various soil test methods including Olsen, Colwell, Bray and Truog have been used to assess the levels of plant-available P (PAP) in soils situated in the highlands of Papua New Guinea (PNG). Up until now, though, there has been no guarantee that these tests provide valid assessments of PAP in these somewhat atypical organic matter-rich tropical soils. Furthermore, the critical soil-P concentrations associated with the tests have been based on studies conducted elsewhere in sub-tropical and temperate latitudes and as such may or may not be valid for soils or cropping situations in PNG. Soil (Colwell)- P and leaf-P data collected during a recent survey of sweet potato gardens in the highlands of PNG were therefore used to determine if useful relationships existed between these variables for different groups of soils, and if they do, to use these relationships to evaluate critical soil Colwell-P concentrations corresponding to a known critical concentration of P in sweet potato index leaf tissue. Separate, highly significant linear relationships were obtained between leaf-P and Colwell-P for soils of volcanic and non-volcanic origins. Based on these relationships, the critical Colwell-P concentration for volcanic soils was found to be four times greater than that for non-volcanic soils, presumably because much of the P extracted from the former soils with alkaline sodium bicarbonate had been chemically ‘fixed’ via sorption and precipitation reactions with sesquioxides and rendered unavailable to plants at ambient soil pH. These critical Colwell-P concentrations if adopted as benchmark values for the soil groups in question should ensure that the results of future soil fertility surveys involving Colwell-P assessments are correctly interpreted.

Ramakrishna, A. & Kirchhof, G. (2008). An evaluation of nutritional constraints on sweet potato (Ipomoea batatas) production in the central highlands of Papua New Guinea. Plant and Soil. 316, 97-105.

Sweet potato (Ipomoea batatas) is the staple food crop in the highlands of Papua New Guinea (PNG). Declining crop productivity, however, appears to be threatening the sustainability of sweet potato-based farming systems within the region, a probable cause being the exhaustion of soil nutrient reserves in continuously cultivated sweet potato gardens. To assess the extent of the problem, a survey of sweet potato gardens was conducted across four of the highlands provinces and information on soil and crop variables was obtained for old gardens (cultivated over many seasons) and new gardens (newly brought into cultivation) on soils of volcanic and non-volcanic origin. Crop leaf nutrient data collected in the survey were interpreted using the Diagnosis and Recommendation Integrated System (DRIS), to try to identify the main nutritional constraints on tuber production in different garden types on soils of volcanic or non-nonvolcanic origin. The results suggested that K deficiency was the primary cause of poor crop production in almost a third of sweet potato gardens, but was more of a problem in old gardens than in new. Phosphorus deficiency was also a problem on volcanic soils, and S deficiency on non-volcanic soils. These latter deficiencies, however, were at least as prevalent in new gardens as in old. Important factors contributing to K and S depletion from garden systems were the removal of K and S-rich vines from cultivation areas, the shortening of fallow periods and the burning of weed and crop residues, the latter releasing S (SO2) to the atmosphere. Correction of K and S deficiencies may require the recycling of old vines back to sweet potato cultivation areas and the adoption of a zero-burn policy for fallow management. Correction of P deficiency may necessitate the use of P-accumulating fallow species, e.g. wild Mexican sunflower (Tithonia diversifolia), to extract the P fixed by sesquioxide and allophanic minerals.

Kirchhof, Odunze, Salako, SOIL MANAGEMENT PRACTISES IN THE NORTHERN GUINEA SAVANNA OF NIGERIA, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G. Kirchhof, p43-48. (http://www.aciar.gov.au/publication/TR71)

A survey of soil management practices was conducted in the northern Guinea savanna of Nigeria. Fifteen villages were randomly selected from a geographical grid covering an area of 100 × 200 km located in the benchmark area of the Ecoregional Program for the Humid and Sub-humid Tropics of Sub-Saharan Africa. In each village the chief and several farmers were interviewed to assess their soil management methods and attitude towards the need to conserve soil. A total of 181 farmers were interviewed in late 1996. The most common crop rotation systems were food legumes with non-legume crops (40%), followed by monocropping (28%). Fifty-three per cent of the farmers who included food legumes in their rotations did so for soil fertility considerations, while 49% of the farmers who practised monocropping did so to maximise their output. These practices indicate that farmers were well aware of the importance of legumes for maintaining soil fertility. Only 2% of the farmers practised mulching with crop residue. The most common use of crop residue was for fodder, the remainder largely being used as building material or else burnt. As a consequence, soil surfaces were generally bare at the onset of the rainy season and hence prone to soil erosion. Ridging was the most important land preparation technique (88%), with farmers perceiving benefit in terms of improved crop emergence (56%) and water conservation (11%). Other benefits included weed control. Ridging was generally practised along contours, with most farmers citing soil conservation benefits, e.g. water conservation, and erosion control as the reasons for using contour ridging. Those farmers who purposely ridged up and down the slope did so for drainage purposes. All farmers used the same method to build ridges—the ridge from the previous year was cut in the middle and the two halves of neighbouring ridges were combined to form a new ridge in the furrow from the previous year. According to the farmers, this method controlled weeds and improved emergence. None of the farmers practised rebuilding old ridges, similar to permanent ridges. Such a practice might be acceptable to farmers in that it may be less labour intensive to rebuild partially collapsed ridges compared to reridging completely. Soil physical benefits from semi-permanent ridging would include increased soil structural stability, reduced soil compaction and increased root proliferation into the subsoil. Negative side effects might include reduced crop emergence and increased weed infestation. The most commonly used tools for soil preparation were hand hoes (80%), followed by draft animals (16%) and tractors (3%).

Salako, F. K., Tian, G., Kirchhof G. 2008. Soil chemical properties and crop yields on an eroded Alfisol managed with herbaceous legumes under yam-maize rotation. Nigerian Journal of Soil Science 18:1-9

This study was carried out in Ibadan, southwestern Nigeria between 1997 and 1999 to determine changes in soil chemical properties and yields on a previously eroded Alfisol. A factorial experiment in which legumes (Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides) and residue management (burned and mulched residues) were factors was set up in two replicates of runoff plots. Yam was planted in 1997 and 1999 whereas maize + legume intercrops were planted in 1997. Soil properties measured were particle size distribution, pH, organic C, total N, Ca, Mg, Mn, exchangeable acidity and effective cation exchange capacity. There was increased acidity at the site. Soil chemical properties were significantly improved by burning of cowpea and Pueraria residues and mulching with Mucuna. Yam tuber yields of 14-18 t ha-1 in 1997 was

Kolawole, G. O. and G. Tian (2007). Phosphorus fractionation and crop performance on an alfisol amended with phosphate rock combined with or without plant residues. African Journal of Biotechnology 6(16): 1972-1978.

The effects of Sokoto phosphate rock ( PR) and plant residues on soil phosphorus ( P) fractions and crop performance was studied in the field on an alfisol in the derived savanna of southwestern Nigeria. The plant residues studied were leaves of Dactyladenia barteri, Flemingia macrophylla, Gliricidia sepium, Leucaena leucocephala, maize ( Zea mays) stover and rice ( Oryza sativa) straw. They were applied alone or in combination with phosphate rock. The PR was applied at a rate of 60 kg P ha(-1) and the plant residues at 5 ton dry matter ha(-1) during the onset of the major rainy season. Plots without PR and plant residues application were included as control. After four weeks incubation period of PR and plant residues, Crotalaria ochroleuca ( shrub legume) was planted in 1999 and maize ( Zea mays) was planted in 2001 as test crops. When PR was not combined with plant residues, incubation of Dactyladenia residues increased resin P from 0.13 to 0.79 mg P kg(-1) at 4 weeks after incubation ( WAI). Other plant residues did not cause appreciable changes in resin P. Application of Leucaena residues increased NaOH-extractable inorganic P ( Pi) from 14.36 to 20.47 mg P kg(-1) at 4 WAI. Total extractable P increased under all the plant residues at 4 WAI but decreased at 8 WAI. When PR was combined with plant residues, there were increases in almost all the P fractions under the plant residues at 4 WAI followed by decreases at 8 WAI. Averaged across P levels, addition of Leucaena residues resulted in higher resin P, NaOH- Pi, residual P and total extractable P compared with the other plant residue treatments. Averaged across residue treatments, resin P increased from 0.12 mg P kg(-1) to 0.75 mg P kg(-1) at 4 WAI and decreased to 0.08 mg P kg- 1 at 8 WAI. All other P pools showed similar trends but with less pronounced decreases at 8 WAI. When PR was not applied with plant residues, Crotalaria dry matter correlate positively with NaHCO3- Pi ( R-2 = 0.59), NaOH- Pi ( R-2 = 0.53) and total extractable P ( R-2 = 0.50), while Crotalaria P uptake correlate positively with NaHCO3- Pi ( R2 = 0.50) at 4 WAI. Maize grain yield and P uptake did not correlate with any of the P fractions. However, when PR was applied with plant residues, maize P uptake was positively correlated with resin P ( R-2 = 0.53) while Crotalaria dry matter ( R2 = 0.60) and P uptake ( R-2 = 0.49) correlate positively with NaOH- Po at 4 WAI. Application of PR alone did not affect yields and P uptakes of Crotalaria and maize crops. Compared with the control without residues, Crotalaria dry matter production and P uptake increased significantly when residues were applied. Interaction effects between PR and Leucaena and rice straw residues on Crotalaria dry matter production and P uptake was significant. Interaction effects between PR and plant residues on maize yield and P uptake were not significant. Our results suggest that combined application of PR with selected plant residues may enhance P dissolution from PR and improve crop performance in some cases.

Adejuyigbe, C., G. Tian and G. Adeoye (2006). Microcosmic study of soil microarthropod and earthworm interaction in litter decomposition and nutrient turnover. Nutrient Cycling in Agroecosystems 75(1-3): 47-55.

A microcosm experiment was set up under laboratory conditions and verified under field conditions with the objective of investigating the interaction of soil microarthropods and earthworms in litter decomposition, nutrient release, and uptake by maize crop. The treatments included: soil alone (control), soil with leaf litter (Senna siamea leaves), soil with leaf litter and soil microarthropods, soil with leaf litter and earthworms (Hyperiodrilus africanus), and soil with litter and both of the soil faunal groups. After an 8-week incubation period, the amounts of litter decomposed and N, P, K, Ca, and Mg released followed the order: with microarthropods and earthworms > with earthworms > with microarthropods > no faunal addition. The presence of microarthropods and earthworms also increased the net level of mineral N in the incubated soil. The additive roles of soil microarthropods and earthworms were observed on decomposition and nutrient release. Such faunal interactions resulted in an increased N uptake by maize in the incubated soil. Despite their lower biomass, soil microarthropods contributed significantly to nutrient turnover in the presence of earthworms. This study emphasizes the need to quantify and devise ways of controlling and regulating the abundance and activities of soil fauna for effective nutrient cycling and, consequently, for better crop yields in low-input tropical agricultural ecosystems.

Oladeji, O. O., G. O. Kolawole, G. O. Adeoye and G. Tian (2006). Effects of plant residue quality, application rate, and placement method on phosphorus availability from Sokoto rock phosphate. Nutrient Cycling in Agroecosystems 76(1): 1-10.

Plant residues are being suggested as an amendment to enhance P release from rock phosphate, however, plant residue enhanced P release could depend on the residue quality, application rate and placement method. Effects of plant residue quality, application rate and placement method on solubility and P release from rock phosphate ( PR) were studied in laboratory and field experiments. Leaves of ten woody and herbaceous species were incubated in a P-deficient soil with Sokoto PR under laboratory conditions to study the effects of residue quality on P release from PR. Effects of residue application rate and placement method were investigated in a field trial with five rates (0, 1, 2, 4 and 8 t DM ha(-1)) of leaves of Dactyladenia barteri, two placement methods (incorporation and mulching), and two levels of Sokoto PR (0 and 60 kg P ha(-1)) in a split-split plot design replicated three times. The plant residues were applied 4 weeks before the main season planting. Maize (main season) followed by cowpea (minor season) was used as test plant. In the laboratory incubation study, addition of plant residues increased the soil pH. Phosphorus released at 8 weeks was greater for plant residues with high C/N ratio, and low magnesium and potassium. In the field trial, soil pH was not affected by the addition of plant residues. Residue placement method showed little effects on P availability from PR. When residues were incorporated with PR, soil Olsen P was highest at lower rates of residues (1 and 2 t DM ha(-1)) at maize planting. Maize P concentration and P uptake were highest at the incorporation of 4 t DM ha(-1) residues with PR. Incorporation at higher rate (8 t DM ha(-1)) resulted in the greatest P uptake of the second crop, cowpea. The study shows the potential of plant residues in enhancing P release from PR. However, there could be initial immobilization of P, but this could be overcome within a short period if residues of high C/N ratio are used. A lower rate of residues (1-4 t DM ha(-1)) is efficient at releasing PR-P for short-term effect especially if incorporated

Kolawole, G. O., G. Tian and H. Tijani-Eniola (2005). Effects of fallow duration on soil phosphorus fractions and crop P uptake under natural regrowth and planted Pueraria phaseoloides fallow systems in southwestern Nigeria. Experimental Agriculture 41(1): 51-68

Sod phosphorus fractions, maize and cassava P uptakes in natural regrowth fallow and Pueraria phaseoloides fallow systems, as affected by the duration (1-3 years) of fallow, were assessed in 1998 and 1999 in a long-term fallow management trial, established in 1989 at the International Institute of Tropical Agriculture, Ibadan, Nigeria. After one and three years fallow respectively, the mean P accumulation in fallow vegetation was 4.2 and 9.4 kg ha(-1) in 1998, and 8.9 and 12.1 kg ha(-1) in 1999 for natural fallow. For Pueraria, the corresponding values were 6.3 and 7.4 kg ha(-1) in 1998 and 6.1 and 13.5 kg ha(-1) in 1999. The positive effects of fallow lengths on dry matter and P accumulation were not as pronounced under Pueraria. Continuous cropping reduced soil pH and depleted Olsen P more than crop-fallow rotations under both fallow systems. An increase in fallow duration enhanced the availability of resin P2NaHCO3-, and NaOHextractable P fractions, especially under natural fallow. Continuous cropping in a natural fallow system resulted in lower resin inorganic P (P-i) and NaHCO3 -extractable inorganic and organic P (P-o) fractions, and higher refractory P fractions (concentrated HCl-extractable P-i and P-o and residual P) as compared to crop-fallow rotations. Although continuous cropping in the Pueraria system resulted in higher refractory P fractions than the crop-fallow rotations, the effects of fallow length on P fractions were not consistent or pronounced. Maize and cassava P uptakes increased with fallow duration. Phosphorous in maize grain was positively correlated with fallow vegetation P accumulation. Total P uptake by maize was positively but weakly correlated with NaHCO3-P-o, Olsen P and fallow vegetation P accumulation.

Tian, G., B. T. Kang, G. O. Kolawole, P. Idinoba and F. K. Salako (2005). Long-term effects of fallow systems and lengths on crop production and soil fertility maintenance in West Africa. Nutrient Cycling in Agroecosystems 71(2): 139-150.

In the development of short fallow systems as alternatives to shifting cultivation in West Africa, a long-term trial was established at the International Institute of Tropical Agriculture (IITA) on an Alfisol in the forest-savanna transitional zone of southwestern Nigeria, comparing three fallow systems; natural regrowth fallow, cover crop fallow and alley cropping on soil productivity and crop yield sustainability. The natural fallow system consisted of natural regrowth of mainly Chromolaena odorata shrub as fallow vegetation. The cover crop fallow system consisted of Pueraria phaseoloides, a herbaceous legume as fallow vegetation. The alley cropping system consisted of woody hedgerows of Leucaena leucocephala as fallow vegetation. The fallow lengths were 0 (continuous cropping), 1, 2 and 3 years after 1 year of maize/cassava intercropping. Biomass produced from natural fallow and cover crop fallow was burnt during the land preparation. Fertilizer was not applied throughout the study. Without fertilizer application, maize yield declined from above 3.0 t ha(-1) to below 0.5 t ha(-1) during 12 years of cultivation (1989-2000) on a land cleared from a 23-year old secondary forest. Temporal change in cassava tuber yield was erratic. Mean maize grain yields from 1993-2000 except for 1999 were higher in cover crop fallow system (1.89 t ha(-1)) than in natural fallow system (1.73 t ha(-1)), while natural fallow system outperformed alley cropping system (1.46 t ha(-1)). During the above 7 years, mean cassava tuber yield in cover crop system (7.7 t ha(-1)) did not differ from natural fallow system (8.2 t ha(-1)), and both systems showed higher cassava tuber than the alley cropping system (5.7 t ha(-1)). The positive effect of fallowing on crop yields was observed for both crops in the three systems, however, insignificant effects were seen when fallow length exceeded 1 year for cover crop and alley cropping, and 2 years for natural fallow. Soil pH, organic carbon, available P and exchangeable Ca, Mg and K decreased considerably after 12 years of cultivation, even in a 3-year fallow subplot. After 12 years, soil organic carbon (SOC) within 0-5 cm depth in alley cropping (13.9 g kg(-1)) and natural fallow (13.7 g kg(-1)) was higher than in cover crop fallow (11.6 g kg(-1)). Whereas significant increase in SOC with either natural fallow or alley cropping was observed only after 2 or 3 years of fallow, the SOC in the 1-year fallow alley cropping subplot was higher than that in continuous cropping natural fallow subplot. It can be concluded from our study that in transforming shifting cultivation to a permanent cropping, fallow with natural vegetation (natural fallow), herbaceous legumes (cover crop fallow) and woody legumes (alley cropping) can contribute to the maintenance of crop production and soil fertility, however, length of fallow period does not need to exceed 2 years. When the fallow length is reduced to 1 year, a better alternative to natural regrowth fallow would be the cover crop for higher maize yield and alley cropping for higher soil organic matter. For fallow length of 2 years, West African farmers would be better off with the natural fallow system.

Kolawole, G. O., H. Tijani-Eniola and G. Tian (2004). Phosphorus fractions in fallow systems of West Africa: Effect of residue management. Plant and Soil 263(1-2): 113-120.

The effects of burning, incorporation and surface mulching after one year of natural regrowth (NF) and Pueraria cover crop fallows on soil P fractions and maize and cassava yields were assessed. Data were collected between 1998 and 2000 as part of an on-going long-term fallow management trial established in 1989 at the International Institute of Tropical Agriculture (IITA), Ibadan, in the derived savanna zone of southwestern Nigeria. After NF in 1998, burning temporarily increased resin- (63%) and NaOH- (19%) extractable inorganic P fractions when compared with mulching and incorporation. Organic P and total extractable P decreased as the season progressed. Fallow systems and residue management options had no consistent and significant effect on P fractions. For both years after W and in 1998, after Pueraria fallow, residue management options had no significant effect on cassava yield. However, in 1999 (wetter year), compared with burning and surface mulching, incorporation of Pueraria fallow residues improved maize and cassava yields. Similarly, maize yield was improved in 1999 with incorporation of NF residues. Maize yield increases due to incorporation of NF residues were 23% compared with burning and 49% compared with mulching. Maize yield increases due to incorporation of Pueraria residues were 37% compared with burning and 47% compared with mulching. Cassava yield was increased by 31% compared with burning and by 26% compared with mulching. Longer period of time may be required to assess whether differences in soil P fractions and crop yields will occur between fallow systems.

Li, Y., G. Tian, M. J. Lindstrom and H. R. Bork (2004). Variation of surface soil quality parameters by intensive donkey-drawn tillage on steep slope. Soil Science Society of America Journal 68(3): 907-913.

Few direct measurements are made to quantify the erosion from upstope to lower field boundaries by intensive tillage. We conducted 50 plowing operations over a 5-d period using a donkey-drawn mold-board-plow on steep backslope in the Chinese Loess Plateau. Topographic changes at different slope positions were quantified using differential global positioning system (DGPS). Soil organic matter (SOM), extractable P and N, and soil bulk density were measured along a downslope transect after each 10-tillage series. Fifty operations resulted in a decrease in maximum soil surface level (SSL) of 1.25 m in the upper slope position and an increase of 1.33 m at the bottom of the slope. Slope gradients decreased from 37 to 14degrees at the upper position and from 18 to 0degrees at the lower position. Surface soil bulk density increased from 1.14 to 1.28 Mg m(-1) in the upper slope and decreased from 1.10 to 1.03 Mg m(-3) in the middle slope. Mean SOM concentrations in the upper and middle positions of the slope decreased from 8.3 to 3.6 g kg(-1), mineral N from 43.4 to 17.4 mg kg(-1), and Olsen-P from 4.5 to 1.0 mg kg(-1). Intensive tillage resulted in a short-term increase in SOM and available nutrients in the lower portion during the tillage operations. Geomorphologic evolution and landscape variability of dissected hillslopes are attributable to soil movement and resulting physical and fertility degradation induced by intensive tillage.

Tian, G. and G. O. Kolawole (2004). Comparison of various plant residues as phosphate rock amendment on savanna soils of West Africa. Journal of Plant Nutrition 27(4): 571-583.

Phosphate rock (PR) is being considered as an important source for phosphorus (P) replenishment in sub-Saharan Africa soils. Field trials were conducted with two-season crops to compare the utilization of PR combined with or without plant residues by test crops. The plant residues studied include leaves of Dactyladenia barteri, Flemingia macrophylla, Gliricidia sepium, and Leucaena leucocephala, maize (Zea mays) stover, and rice (Oryza sativa) straw. The test plants were Crotalaria ochroleuca (legume cover crop) and maize (Zea mays) in sequential cropping systems. Where no plant residues were applied, apparent utilization efficiency (AUE) of PR was 1.0% in 1999 and 2.7% in 2001. The AUE of PR was improved in many cases with the addition of plant residues. The AUE of PR in all treatments with plant residues was on average 3.4% in 1999 and 6.2% in 2001 with a pronounced effect from Flemingia and Gliricidia. Negative values of AUE were observed in treatments with Leucaena and maize stover in 1999, and Dactyladenia in 2001. These results suggest that the choice of plant residues is an important step for using plant residues as PR amendment on the near-neutral and neutral soils of West Africa.

Kolawole, G. O., G. Tian and H. Tijani-Eniola (2003). Dynamics of phosphorus fractions during fallow with natural vegetation and planted Pueraria phaseoloides in south-western Nigeria. Plant and Soil 257(1): 63-70.

A study was conducted in 1998 and 1999 on a long-term fallow management trial, established in 1989 at the International Institute of Tropical Agriculture (IITA), Ibadan, in the derived savanna of southwestern Nigeria, to quantify P fractions under natural fallow (NF) and a Pueraria cover crop fallow. Plots with previous 1: 1, 1: 2, and 1: 3 crop/fallow ratios before reverting to fallow in either 1998 or 1999 were considered. Biomass accumulation under the two fallow types was comparable and increased linearly with fallow age, reaching slightly above 7 t dry matter ha(-1) after 8 months of fallow. Phosphorus accumulation in the fallow vegetation ranged from 2.1 - 9.1 kg ha(-1) for natural fallow (NF) and from 1.5 - 6.6 kg ha(-1) for Pueraria. Magnesium was also higher under NF (9.1 - 21 kg ha(-1)) than under Pueraria (4.4 - 13 kg ha(-1)), whereas N, Ca, and K contents were higher in Pueraria biomass than under NF at 1 year after fallow. Pueraria fallow tended to lower soil pH compared with NF. However, plots with less frequent cropping ( 1: 3 crop/fallow ratio) did not have significantly different pH irrespective of the fallow vegetation type. Olsen extractable soil P increased as fallow length increased irrespective of the fallow system and previous crop/fallow ratio. For example, under NF ( 0 - 5 cm depth, 1: 1 crop/fallow ratio in 1998) Olsen P increased from 12 mg kg(-1) to 17 mg kg(-1) after 1 year of fallow and under Pueraria, it increased from 8 mg kg(-1) to 15 mg kg(-1). Fallow type and previous crop/fallow ratio had no significant and consistent effects on soil P fractions. However, NaOH- and concentrated HCl- extractable organic P fractions increased with fallow length. In 1998, under NF, NaOH- extractable organic P increased from 12 to 21 mg kg(-1) (1: 1 crop/fallow ratio) and from 10 to 19 mg kg(-1) for both 1: 2 and 1: 3 crop/ fallow ratio. HCl- extractable organic P increased from 11 to 30 mg kg(-1) ( 1: 1 crop/ fallow ratio), from 13 to 27 mg kg(-1) ( 1: 2 crop/ fallow ratio) and from 18 to 35 mg kg(-1) ( 1: 3 crop/ fallow ratio). Similar trend was observed under Pueraria fallow. These results suggest that P was reallocated to non-readily available organic P fractions irrespective of fallow type and previous land use. These organic P fractions, which are usually more stable, reflect the overall change in soil organic P levels when the soil was stressed by cultivation and then reverted to fallow. These pools may thus represent an active reservoir ( source and sink) of P in shifting cultivation under tropical conditions without inorganic fertilizer application.

Tian, G., B. T. Kang and G. O. Kolawole (2003). Effect of fallow on pruning biomass and nutrient accumulation in alley cropping on alfisols of tropical Africa. Journal of Plant Nutrition 26(3): 475-486.

A study was conducted in long-term alley cropping plots established in 1989 at International Institute of Tropical Agriculture (IITA), Ibadan, southwestern Nigeria to determine the seasonal and yearly dynamics of dry matter and nutrient concentrations of hedgerow pruning under continuous cropping and response to fallow of 1-3 years. At one year after Leucaena leucocephala transplanting, pruning was started at the 75 cm height. The pruning frequency increased from one to five times per year as trees grew. In continuous alley cropping without fertilizer application, pruning dry matter decreased gradually from a peak of 5 t ha(-1) at 3 years after Leucaena transplanting to about 2.5 t ha(-1) at 11 years after transplanting, while the ratio of dry season to wet season biomass increased. Within 5 years after establishment, nitrogen (N) and phosphor-us (P) concentrations in pruning decreased and Mg increased with the continuous cropping. Fallow clearly increased pruning biomass and nutrient concentrations. At the completion of the first cycle (1993), the pruning N yield was 170 kg ha(-1) for the continuous cropping plot, and 269 for plots with 1 yr fallow, 344 for plots with 2 yr fallow and 241 kg ha(-1) for plots with 3 yr fallow. In 1993 pruning P yield increased from 6.5 to 10.9 in the continuous alley cropping and in 1995, it increased from 4.5 to 7.0 kg ha(-1) in one-year fallow plots. Fallow effect on potassium (K), calcium (Ca), and magnesium (Mg) yield in pruning was also evident. These results suggest alley cropping with one-year fallow could be an effective rotation system for nutrient cycling in Alfisols of West Africa.

Carsky, R. J., B. Oyewole and G. Tian (2001). Effect of phosphorus application in legume cover crop rotation on subsequent maize in the savanna zone of West Africa. Nutrient Cycling in Agroecosystems 59(2): 151-159.

The benefit of planted fallow with legume cover crops may be limited on P deficient soil. A trial was conducted at two P deficient sites in northern Nigeria to test the hypothesis that application of P to legume cover crop fallow can substitute for N application to subsequent maize. Mainplots consisted of leguminous fallows followed by unfertilized maize, or native (mostly grass) fallows followed by maize with 0 or 40 kg N ha(-1) (Kaduna) and 0, 30 or 60 kg N ha(-1) (Bauchi). Three rates of P (0, 9, and 18 kg ha(-1)) were applied to fallow sub-plots as single superphosphate. In the first year, dry matter accumulation of lablab (Lablab purpureus) responded to P application, while mucuna (Mucuna cochinchinensis) dry matter did not. Lablab mulch dry matter during the dry season was significantly increased by previous season P application while mucuna was not. Previous fallow vegetation was a significant factor for maize growth in the second year but the interaction with P applied to the fallow was not significant at P

Tian, G., J. A. Olimah, G. O. Adeoye and B. T. Kang (2000). Regeneration of earthworm populations in a degraded soil by natural and planted fallows under humid tropical conditions. Soil Science Society of America Journal 64(1): 222-228.

Earthworm populations (predominantly Hyperiodrilus africanus and Eudrilus eugeniae) were sampled monthly for 1 yr during 1994 and 1995 in natural regrowth vegetation fallow (dominated by the natural fallow shrub Chromolaena odorata L.), planted fallow (the woody species Senna siamea Lam., Leucaena leucocephala Lam., and Acacia leptocarpa), and intercropped maize (Zea mays L.)-cassava (Manihot esculenta Crantz) established in 1989 in a degraded Alfisol (Oxic paleustalf) in southwestern Nigeria. Compared to leaves of Chromolaena (3.3% N), N concentrations were lower in those of Senna and Acacia, and higher in Leucaena. Acacia and Leucaena had higher polyphenol relative to the natural fallow (2%), The lignin was lower in Leucaena than the natural fallow leaves (14%). For 65% of the sampling dates, earthworm numbers under all fallows were significantly higher than under continuous maize-cassava, The mean earthworm numbers (no. m(-2)) during the rainy season (April-October) decreased in the following order: Chromolaena (147), Senna (131), Leucaena (92), Acacia (80), and maize-cassava (14). Earthworm fresh weights in fallow plots were higher than in the maize-cassava plot, though this was significant for only 4 out of 11 sampling dates. Higher earthworm numbers and biomass in fallow plots were attributed to higher litterfall, lower soil temperature, and higher soil moisture. The mean earthworm numbers were directly correlated with the mean soil moistures (r(2) = 0.80, P

Badejo, M. A. and G. Tian (1999). Abundance of soil mites under four agroforestry tree species with contrasting litter quality. Biology and Fertility of Soils 30(1-2): 107-112.

Populations of soil-dwelling mites were monitored in monoculture plots of four agroforestry tree species, Gliricidia sepium, Leucaena leucocephala, Dactyladenia barteri and Treculia africana, and compared to those in grass and secondary forest plots in the dry season (December 1993 to January 1994) and in the wet season (April to June 1994) in southwest Nigeria. Mite populations were very low in all plots during the dry season (500-3000 m(-2)), compared to those during the wet season (10 000-30 000 m(-2)). The highest mite population was observed in Gliricidia plots (3 044 m(-2)) for the dry season and Leucaena plots (30 240 m(-2)) for the wet season. Mite genera that were dominant in all the experimental plots were Annectacarus, Haplozetes, Machadobelba, Scheloribates and members of the Galumnidae, Dermanyssidae and Parasitidae. The community structure of mites was similar in the soil for Treculia and Gliricidia plots and for Leucaena and Dactyladenia plots. There were more taxonomic groups of mites under Leucaena than in the other agroforestry plots. Based on the density, diversity and complexity of the mite communities, Leucaena was considered to be better than other agroforestry species in encouraging the growth of mite populations.

Carsky, R. J., B. Oyewole and G. Tian (1999). Integrated soil management for the savanna zone of W. Africa: legume rotation and fertilizer N. Nutrient Cycling in Agroecosystems 55(2): 95-105.

Integrated soil management with leguminous cover crops was studied at two sites in the northern Guinea savanna zone of northern Nigeria, Kaduna (190 day growing season) and Bauchi (150 days). One-year planted fallows of mucuna, lablab, and crotalaria were compared with natural grass fallow and cowpea controls. All treatments were followed by a maize test crop in the second year with 0, 30, or 60 kg N ha(-1) as urea. Above ground legume residues were not incorporated into the soil and most residues were burned early in the dry season at the Kaduna site. Legume rotation increased soil total N, maize growth in greenhouse pots, and dry matter and N accumulation of maize. Response of maize grain yield to 30 kg N ha(-1) as urea was highly significant at both sites and much greater than the response to legume rotation. The mean N fertilizer replacement value from legume rotation was 14 kg N ha(-1) at Kaduna and 6 kg N ha(-1) at Bauchi. With no N applied to the maize test crop, maize grain yield following legume fallow was 365 kg ha(-1) higher than natural fallow at Bauchi and 235 kg ha(-1) higher at Kaduna. The benefit of specific legume fallows to subsequent maize was mostly related to above ground N of the previous legume at Bauchi, where residues were protected from fire and grazing. At Kaduna, where fallow vegetation was burned, maize yield was related to estimated below ground N. The results show that legume rotation alone results in small maize yield increases in the dry savanna zone.

Kang, B. T., F. E. Caveness, G. Tian and G. O. Kolawole (1999). Longterm alley cropping with four hedgerow species on an Alfisol in southwestern Nigeria - effect on crop performance, soil chemical properties and nematode population. Nutrient Cycling in Agroecosystems 54(2): 145-155.

A longterm alley cropping trial was undertaken on an eroded Oxic paleustalf in the forest-savanna transition zone of southwestern Nigeria from 1981-1993. Two nitrogen fixing hedgerow species (Gliricidia sepium and Leucaena leucocephala) and two non legume hedgerow species (Alchornea cordifolia and Dactyladenia barteri) were used in the trial compared to a control (with no hedgerow) treatment. Plots were sequentially cropped with maize (main season) followed by cowpea (minor season). With 4 m interhedgerow spacing and pruning at 0.75 m height, the mean annual pruning biomass yields were observed in the following order: Leucaena (7.1 t ha(-1)) > Gliricidia (4.9 t ha(-1)) > Alchornea (3.7 t ha(-1)) > Dactyladenia (3.0 t ha(-1) ). Alley cropping with the four woody species greatly enhanced the total plot (woody species + crop) biomass yield/ha as follows; Leucaena (21.8 t ha(-1)) > Gliricidia (17.7 t ha(-1)) > Alchornea (11.7 t ha(-1)) > Dactyladenia (9.5 t ha(-1)). Total biomass yield of crops in control plot was 5.3 t ha(-1). Higher biomass yields with alley cropping also increased nutrient yield and cycling. Gliricidia and Leucaena showed higher nutrient yields than Alchornea and Dactyladenia. Alley cropping with Gliricidia and Leucaena could sustain maize yield at moderate level (>2 t ha(-1)), which would require a N-rate of 45 kg N ha(-1) with sole cropping. Application of N in Gliricidia and Leucaena alley cropping still improved maize yield. Higher nitrogen rates are required for alley cropping with Alchornea and Dactyladenia hedgerows. A low rate of phosphorus application is needed for sustaining crop yields with all treatments. Occasional tillage is recommended to increase maize yield. Alley cropping and tillage showed little effect on cowpea seed yield. Surface soil properties declined with time with continuous cultivation. Alley cropping with woody species maintained higher soil organic carbon, phosphorus and potassium levels. Plots alley cropped with Gliricidia and Leucaena showed lower pH and extractable calcium level. Leucaena alley cropped plot also showed lower magnesium level. The decline in soil pH and extractable cations may be due to increased cation leaching with application of high rates of Gliricidia and Leucaena prunings. Alley cropping with the four woody species showed no effect on population of parasitic nematodes.

Okoh, I. A., M. A. Badejo, I. T. Nathaniel and G. Tian (1999). Studies on the bacteria, fungi and springtails (Collembola) of an agroforestry arboretum in Nigeria. Pedobiologia 43(1): 18-27.

The aerobic heterotrophic bacteria, fungal and springtail populations of four monoculture agroforestry plots, a regrowth forest and a grass plot were investigated in September October, and November 1994 so as to throw more light on the relationships between them in a tropical soil. Soil properties, litter composition and temperature and moisture conditions were also investigated. The mean of four replicates was recorded For each parameter. Bacteria and fungi were estimated using a standard pour plate technique while springtails were extracted in a modified Berlese-Tullgren funnel extractor. Bacterial counts were of the order of 10(5) to 10(6) cfu/g while fungal counts were of the order of 10(3) to 10(4) in the experimental plots. There was a predominance of aerobic heterotrophic bacteria over fungi in all the experimental plots. The dynamics of the populations of bacteria. fungi and springtails were different from one another and between experimental plots. Springtail populations declined gradually from September to November in all experimental plots. This trend did not occur fur bacteria and fungi. All experimental plots supported similar bacteria and springtail populations during the period of study but the species composition and diversity of fungal populations differed between plots. Results of correlation studies suggest that there is a negative relationship between springtails and bacteria.

Risasi, E. L., G. Tian, B. T. Kang and E. E. Opuwaribo (1999). Nitrogen mineralization of roots of maize and selected woody species. Communications in Soil Science and Plant Analysis 30(9-10): 1431-1437.

A laboratory experiment was carried out to assess nitrogen (N) mineralization of roots of four woody agroforestry species (Dactyladenia barteri, Senna siamea, Gliricidia sepium, and Leucaena leucocephala) and maize (Zea mays). Addition of Gliricidia and Leucaena roots with high N contents and low carbon (C)-to-N ratio (less than or equal to 14.0) resulted in net N mineralization, while the addition of maize roots with low N and high C-to-N ratio (40.3) immobilized N. Addition of Dactyladenia and Senna roots with intermediate N content and C-to-N ratio immobilized N to a lesser extent. Nitrogen mineralization was negatively and significantly correlated with C-to-N ratio of the added roots. Addition of roots of the five species also differentially affected soil pH during the first 12 weeks of incubation. Soil pH was positively and significantly correlated with the roots initial C-to-N ratio and negatively correlated with their initial N content. At 24 weeks of incubation, the pH of all treatments reverted to initial value.

Badejo, M. A., T. I. Nathaniel and G. Tian (1998). Abundance of springtails (Collembola) under four agroforestry tree species with contrasting litter quality. Biology and Fertility of Soils 27(1): 15-20.

The soil-and litter-dwelling Collembola under four agroforestry tree species (Treculia africana, Dactyladenia Acioa) barteri, Gliricidia sepium and Leucaena leucocephala) were monitored monthly for a period of 12 months and results were compared with those of a secondary forest and a grass plot. Treculia and Dactyladenia produced lower quality litter, leading to lower soil temperature and higher soil moisture under those species, relative to Gliricidia and Leucaena. The agroforestry tree plots contained more soil-and litter-dwelling Collembola than the secondary forest and grass plots. The slowly decomposing litter under Treculia and Dactyladenia supported more litter Collembola than the quickly decomposing litter under Gliricidia and Leucaena. Soil moisture and temperature were, respectively, positively and negatively correlated with populations of soil Collembola. Based on the results of this study, it is suggested that the use of prunings of agroforestry tree species as mulch in agroecosystems would encourage the growth of Collembola populations and enhance their role in decomposition processes.

Tian, G. (1998). Effect of soil degradation on leaf decomposition and nutrient release under humid tropical conditions. Soil Science 163(11): 897-906.

Characterization of degradation of an Alfisol caused by clearing and long-term cultivation and the effect of the degradation on leaf (Cajanus cajan) decomposition and nutrient (N and P) release were studied in the humid zone of southwest Nigeria. Degradation of the Alfisol as a result of land clearing and 17-year continuous cropping led to loss of soil biota and deterioration of soil physical and chemical properties. Compared with nondegraded soil, the degraded soil was 38% lower in soil organic carbon, 55% lower fn exchangeable bases, 56% lower in microbial biomass, and had 44% lower microarthropod density, 34% less silt, and 88% less water infiltration; it also had 13% higher bulk density acid 14% more sand. Soil pH was lower in the degraded than in the nondegraded soil. The macrofauna community in the degraded soil was termite-dominant (Ancistratermes cavithorax), whereas it was earthworm-dominant (Hyperiodrilus africanus) in the nondegraded soil. Leaf decomposition and nutrient release were lower irt the degraded soil than in the nondegraded soil during the 150-day experiment. Higher decreases in leaf decomposition and nutrient release in the degraded soil were observed when macrofauna were excluded. Macrofauna-mediated leaf decomposition and nutrient release in the degraded soil were higher than in the nondegraded soil. Irrespective of soil degradation, macrofauna-mediated decomposition and nutrient release resulted in net nutrient mineralization.

Tian, G. and B. T. Kang (1998). Effects of soil fertility and fertilizer application on biomass and chemical compositions of leguminous cover crops. Nutrient Cycling in Agroecosystems 51(3): 231-238.

The biomass and chemical compositions of selected leguminous cover clops Aeschynomene histrix, Cajanus cajan, Centrosema brasilianum, Centrosema pascuorum, Chamaercrista rotundifolia, Crotalaria verrucosa, Lablab purpureus Psophocarpus palustris, Pseudovigna argentea, Mucuna pruriens, Pueraria phaseoloides, and Stylosanthes I?hamata were studied in a pot experiment, using soil with two fertility levels. Biomass yield responded to soil fertility levels and fertilizer application. The highest response to soil fertility was observed with C. brasilianum (340%, 200% and 310% more shoots, roots and nodules in high fertility soil than low fertility soil without fertilizer application). The highest response to fertilizer application was with P. palustris (500% more shoots with fertilizer than without in high fertility soil), with C. rotundifolia (410% more roots with fertilizer than without in low fertility soil), and with L. purpureus (1330% more nodules with fertilizer than without on high fertility soil). Legumes grown without fertilizer application allocated more biomass to roots than those with fertilizer application. Chamaercrista rotundifolia, L. purpureus, P. argentea, M. pruriens and C. cajan showed higher N content in roots than in shoots. Soil fertility levels did not affect N content of shoot, while fertilizer application increased it by 30%. Except for C. cajan (only shrub species), all the herbaceous legumes had lower lignin content (6-10%) in the shoots. The mean lignin content in roots was above 20% with no fertilizer: and decreased with fertilizer application compared to the no fertilizer treatment. The polyphenol concentration in shoots was higher than in roots.

Tian, G., C. O. Adejuyigbe, G. O. Adeoye and B. T. Kang (1998). Role of soil microarthropods in leaf decomposition and N release under various land-use practices in the humid tropics. Pedobiologia 42(1): 33-42.

The role of microarthropods in leaf decomposition and N release was studied in various land-use practices: secondary forest, bush regrowth, Pueraria phaseoloides relay cropping, Leucaena leucocephala alley cropping, and cropping without cover crop or tree hedgerows (control treatment), using litterbags with mesh-size of 0.5 mm and 0.08 mm for 98 days. Litterbags with 0.5 mm mesh-size allowed access by microarthropods, whereas those with 0.08 mm mesh-size excluded microarthropods. Microarthropod-mediated leaf decomposition and N release varied with the land-use practices, particularly the last named. Inclusion of microarthropods in most cases increased leaf decomposition and N release rates, with the highest value 38 % for decomposition in control treatment and 29 % for N release in relay cropping. A decrease in leaf decomposition rate (10 %) and N release (32 %) was observed in the secondary forest. Microarthropod-mediated leaf decomposition and N release, which mainly occurred in later stages of decomposition, increased as microbial decomposition decreased. The results suggest that microarthropods have a "buffering effect" in regulating leaf decomposition and N release, which is mediated by land-use history.

Beare, M. H., M. V. Reddy, G. Tian and S. C. Srivastava (1997). Agricultural intensification, soil biodiversity and agroecosystem function in the tropics: The role of decomposer biota. Applied Soil Ecology 6(1): 87-108.

Intensification of agriculture in the tropics has resulted from a shortage of farmland and insufficient food production to satisfy the needs of an expanding population. Many tropical farmers are challenged by the prospect of intensifying their production while sustaining or improving the fertility and productivity of soils with only locally available natural resources. The waste products of plant and animal production represent some of the most abundant natural resources available for use by tropical farmers to achieve these goals. The efficient use and management of these resources depends on understanding the role that decomposer biota play in regulating the structure and function of agricultural ecosystems. Furthermore, the development of agricultural management practices which promote the beneficial attributes of these organisms will be essential to sustaining the productivity and environmental integrity of tropical agriculture. Finally, understanding the role of biodiversity among decomposer biota in maintaining the functional properties of tropical agricultural ecosystems is critical to achieving this goal. The objective of this review is to further that understanding by describing the taxonomic and functional diversity of decomposer biota in the tropics and evaluating known links between their diversity and the function of agricultural ecosystems. We further describe the effects of changing land-use and agricultural intensification on the structure and diversity of decomposer communities in the tropics and suggest some priorities for future research

Paustian, K., O. Andren, H. H. Janzen, R. Lal, P. Smith, G. Tian, H. Tiessen, M. Van Noordwijk and P. L. Woomer (1997). Agricultural soils as a sink to mitigate CO2 emissions. Soil Use and Management 13(4): 230-244.

Agricultural soils, having been depicted of much of their native carbon stocks, have a significant CO2 sink capacity. Global estimates of this sink capacity are in the order of 20-30 Pg C over the next 50-100 years. Management practices to build hip soil C must increase the input of organic matter to soil and/or decrease soil organic matter decomposition rates. The most appropriate management practices to increase soil C vary regionally, dependent on both environmental and socioeconomic factors. In temperate regions, key strategies involve increasing cropping frequency and reducing bare fallow, increasing the use of perennial forages (including N-fixing species) in crop rotations, retaining crop residues and reducing or eliminating tillage (i.e. no-till). In North America and Europe, conversion of marginal arable land to permanent perennial vegetation, to protect fragile soils and landscapes and/or reduce agricultural surpluses, provides additional opportunities for C sequestration. In the tropics, increasing C inputs to soil through improving the fertility and productivity of cropland and pastures is essential. In exclusive systems with vegetated fallow periods (e.g. shifting cultivation), planted fallows and cover crops can increase C levels over the cropping cycle. Use of no-till, green manures and agroforestry are other beneficial practices. Overall, improving the productivity and sustainability of existing agricultural lands is crucial to help reduce the rate of new land clearing, from which large amounts of CO2 from biomass and soil are emitted to the atmosphere, Some regional analyses of soil C sequestration and sequestration potential have been performed, mainly for temperate industrialized countries. More are needed, especially for the tropics, to capture region-specific interactions between climate, soil and management resources that are lost in global level assessments. By itself C sequestration in agricultural soils can make only modest contributions (e.g. 3-6% of total fossil C emissions) to mitigating greenhouse gas emissions. However, effective mitigation policies will not be based on any single 'magic bullet' solutions, but rather on many modest reductions which are economically efficient and which confer additional benefits to society. In this context, soil C sequestration is a significant mitigation option. Additional advantages of pursuing strategies to increase soil C are the added benefits of improved soil quality for improving agricultural productivity and sustainability.

Tian, G. and L. Brussaard (1997). Mulching effect of plant residues of chemically contrasting compositions on soil organic matter content and cation exchange capacity. Communications in Soil Science and Plant Analysis 28(17-18): 1603-1611.

Effects of five types of plant residues [Acioa, presently Dactyladenia barteri, Gliricidia sepium, and Leucaena lecocephala prunings, maize (Zea mays) stover and rice (Oryza sativa) straw] applied as mulch on soil organic matter (SOM) content and effective cation exchange capacity (ECEC) were studied on an Alfisol in the humid tropics. Plant residue mulch resulted in a decline in SOM and ECEC during two years of cropping following six years of grass fallow. Rice straw mulch resulted in less and maize stover mulch in a greater decrease of SOM and ECEC than the other mulches. Decrease in SOM and ECEC is attributed to the mulching effect on the soil micro-climate which enhanced the decomposition of SOM accumulated during the grass fallow prior to the initiation of the experiment. In order to maintain SOM for a tropical soil, plant residues with high lignin, polyphenols, and silica will have to be among residue species when applied in continuous cropping systems.

Tian, G., B. T. Kang and L. Brussaard (1997). Effect of mulch quality on earthworm activity and nutrient supply in the humid tropics. Soil Biology & Biochemistry 29(3-4): 369-373.

An experiment was conducted in 1990 and 1991 at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria to study the role of earthworms in the decomposition of plant residue mulches with different qualities. Five mulches of Dactyladenia barteri, Gliricidia sepium, Leucaena leucocephala prunings, maize (Zea mays) stover and rice (Oryza sativa) straw, which had a wide range of C-to-N ratio, lignin and polyphenol concentrations were studied. Based on their chemical compositions, Dactyladenia prunings were defined as low-quality mulch, Leucaena and Gliricidia prunings as high quality-mulches, and maize stover and rice straw as intermediate-quality mulches. The mean density of earthworms (Hyperiodrilus africanus and Eudrilus eugeniae) in the experimental plots decreased in the following order: high quality > intermediate quality > low quality mulches. High quality mulch (Leucaena and Gliricidia prunings) supported 54% higher earthworm populations than the (no mulch) control, whereas low-quality mulch (Dactyladenia prunings) only increased earthworm density by 15%, compared to the control in 1990. Plots with Leucaena and Gliricidia prunings had the highest earthworm populations at the initial stage of the experiment, while the other treatments showed increased earthworm numbers at a later stage. Effects of earthworms on mulch decomposition were examined in the field in large pots with or without earthworms (Eudrilus eugeniae). The effects of earthworms were more pronounced for Dactyladenia prunings (low quality), than for Leucaena and Gliricidia prunings (high quality). The results indicate that manipulation of earthworm activity with application of high- and low-quality mulches may improve the synchronization of soil nutrient supply and crop nutrient demand.

Sanginga, N., L. E. Wirkom, A. Okogun, I. O. Akobundu, R. J. Carsky and G. Tian (1996). Nodulation and estimation of symbiotic nitrogen fixation by herbaceous and shrub legumes in Guinea savanna in Nigeria. Biology and Fertility of Soils 23(4): 441-448.

Twelve herbaceous and shrub legume species were grown in pot and field experiments in five sites representing three agroecological zones in moist savanna in Nigeria. The objectives were to: (1) assess natural nodulation of the legumes and characterize their indigenous rhizobia, (2) determine their need for rhizobia inoculation and (3) estimate the amount of N-2 fixed by each of these legumes. At 4 weeks after planting (WAP), Crotolaria verucosa was not nodulated at any of the sites while Centrosema pascuorum had the highest number of nodules in all sites. At 8 WAP, all legumes were nodulated, with Mucuna pruriens having the least number of nodules and Stylosanthes hamata the highest. The number of nodules, however, was inversely correlated to the mass of nodules. Significant differences in nodulation of the legume species grown in the field also occurred between and within sites. Mucuna pruriens and Lablab purpureus produced more shoot and nodule biomass than the other legumes in all sites. Growth of most of these legumes responded to fertilizer application, except for C. verrucosa and Aeschynomene histrix. Except for C. verrucosa, average proportion of N-2 fixed was about 80% and this was reduced by about 20% with N fertilizer application. The majority of rhizobia isolates (60%) were slow growing, belonging to the Bradyrhizobia spp. group. Selected rhizobia isolates evaluated on Cajanus cajan, C. pascuorum, M. pruriens and Psophocarpus palustris varied from ineffective to highly effective in Leonard jar conditions. However, only growth of M. pruriens responded to inoculation in potted soils, whereas it was lower than that obtained with N fertilizer application. This indicated the need to screen more rhizobia in order to improve N-2 fixation and growth of legume species such as M. pruriens when it is introduced in soils deficient in N.

Tian, G. and B. T. Kang (1996). A simplified Shaw's wet-combustion technique for determination of carbon in plant materials. Communications in Soil Science and Plant Analysis 27(11-12): 2543-2548.

A simplified Shaw's wet-combustion technique for carbon (C) determination in plant materials is described which requires less reagent and operation time. The simplified technique gave high recovery (99.4%) of the C in analytical pure grade sucrose and citric acid, and high reproducibility of C measured in 18 different plant materials.

Tian, G., B. T. Kang and L. J. Lambourne (1996). Ruminant assay for rapidly estimating plant residue decomposability in the field. Pedobiologia 40(6): 481-483.

Field litterbag decomposition study, through widely accepted for examining decomposition of plant residues, is time consuming, as it requires several months to complete. An experiment was conducted to explore the possibility to introduce ruminant nylonbag assay which only takes 3-4 days, to plant residue decomposition studies for agricultural purpose. Results showed decomposability of plant residues, measured using the ruminant nylonbag significantly correlated with those using the litterbags, indicating that the ruminant nylonbag assay, widely used for studying herbage breakdown in animal nutrition research, can be used for rapidly estimating the decomposability of plant residues in the field.

Tian, G., L. Brussaard and B. T. Kang (1995). AN INDEX FOR ASSESSING THE QUALITY OF PLANT RESIDUES AND EVALUATING THEIR EFFECTS ON SOIL AND CROP IN THE (SUB-)HUMID TROPICS." Applied Soil Ecology 2(1): 25-32.

An equation was developed for calculating a plant residue quality index (PRQI) in the (sub-)humid tropics using the C/N ratio and lignin and polyphenol concentration of plant residues. Among 18 plant species tested, there was a large variation in PRQI. The PRQI was correlated with the decomposition rate of plant residues, soil microclimate, soil fauna density and maize crop performance in the field. Soil moisture and termite density increased with decreases in PRQI, whereas decomposition rate constants of plant residues, soil temperature and ant density increased with increase in PRQI. Improvement in crop performance, such as grain yield, by plant residue mulching was lowest in the case of intermediate PRQI. It is concluded that PRQI can be used for selecting plant residues and projecting their agronomic value in the tropics.

Tian, G., L. Brussaard and B. T. Kang (1995). BREAKDOWN OF PLANT RESIDUES WITH CONTRASTING CHEMICAL-COMPOSITIONS UNDER HUMID TROPICAL CONDITIONS - EFFECTS OF EARTHWORMS AND MILLIPEDES. Soil Biology & Biochemistry 27(3): 277-280

The effects of tropical earthworms (Eudrilus eugeniae) and millipedes (Spirostreptidae) on the breakdown of plant residues [Acioa (presently, Dactyladenia) barteri, Gliricidia sepium and Leucaena leucocephala prunings, maize (Zea mays) stover and rice (Orysa sativa) straw], with contrasting chemical compositions, were studied in the field under humid tropical circumstances. Addition of earthworms significantly increased the breakdown of maize stover. Addition of millipedes significantly increased the breakdown of maize stover and rice straw. Combined addition of earthworms and millipedes generally resulted in greater plant residue breakdown, compared to that of a single group of fauna. During 10 weeks of exposure, earthworms and millipedes, on average, accounted for the breakdown of all plant residues by 10.4 and 28.4%, respectively. Millipedes and earthworms contributed more to the breakdown of plant residues with low quality (high C-to-N ratio, lignin and polyphenol contents) than to the degradation of those with high quality. It is concluded that fauna-enhanced breakdown of plant residues will have different effects on soil nutrient supply, depending on residue quality.

Swift, M. J., K. A. Dvorak, K. Mulongoy, M. Musoko, N. Sanginga and G. Tian (1994). THE ROLE OF SOIL ORGANISMS IN THE SUSTAINABILITY OF TROPICAL CROPPING SYSTEMS

Tian, G., B. T. Kang and L. Brussaard (1993). MULCHING EFFECT OF PLANT RESIDUES WITH CHEMICALLY CONTRASTING COMPOSITIONS ON MAIZE GROWTH AND NUTRIENTS ACCUMULATION. Plant and Soil 153(2): 179-187

Effects of application of prunings of three woody species (Acioa barteri, Gliricidia sepium and Leucaena leucocephala), maize (Zea mays L.) stover and rice (Oryza sativa L.) straw as mulch on maize were studied on an Alfisol in southern Nigeria in 1990 and 1991. Maize dry matter and grain yield were higher with applications of plant residues and N fertilizer in both years. Addition of Leucaena prunings gave the highest maize grain yield in both years. Compared to the 1990 results, Acioa showed the least grain yield decline among the mulch treatments in 1991. Nutrient uptake was enhanced by applications of plant residues. Leucaena prunings had the highest effect in both years and increased the mean N, P, and Mg uptake by 96%, 84%, and 50%, respectively, over the control. Addition of Acioa prunings increased K and Ca uptake by 59% and 92%, respectively, over the control. 'High quality' (low CIN ratio and lignin level) plant residues enhance crop performance through direct nutritional contributions, whereas 'low quality' (high C/N ratio and lignin level) plant residues do so through mulching effects on the microclimate. 'Intermediate quality' plant residues have no clear effects on crop performance.

Tian, G., L. Brussaard and B. T. Kang (1993). "BIOLOGICAL EFFECTS OF PLANT RESIDUES WITH CONTRASTING CHEMICAL-COMPOSITIONS UNDER HUMID TROPICAL CONDITIONS - EFFECTS ON SOIL FAUNA." Soil Biology & Biochemistry 25(6): 731-737.

Effects of application of five types of plant residues [Acioa barteri, Gliricidia sepium and Leucaena leucocephala prunings, maize (Zea mays) stover and rice (Oryza sativa) straw] as mulch on soil fauna were examined under field conditions in the humid tropics in 1990 and 1991. Earthworm mean population over 2 years was higher under any type of plant residues by 41% compared to control. Leucaena prunings supported the highest earthworm population. Mulched plots also showed 177% higher mean termite population over 2 years than control. Highest termite population was observed in plots mulched with Acioa prunings followed by maize stover > rice straw > Leucaena prunings > Gliricidia prunings. The mean ant populations were 36% higher with Leucaena and Gliricidia prunings, and were not affected by Acioa prunings, maize stover and rice straw as compared to control. Millipede populations were not significantly affected by mulching. Earthworm populations were negatively correlated with the ratio of lignin: N of plant residues. Ant populations were significantly related to the N content of plant residues (R2 = 0.87 and 0.84 for 1990 and 1991 respectively). The results imply that chemical plant composition, particularly N and lignin contents, play a critical role in faunal abundance in the soil through their effect on palatability and decomposibility. Indirect microclimatic and mulching effects may also be important.

Tian, G., B. T. Kang and L. Brussaard (1992). BIOLOGICAL EFFECTS OF PLANT RESIDUES WITH CONTRASTING CHEMICAL-COMPOSITIONS UNDER HUMID TROPICAL CONDITIONS - DECOMPOSITION AND NUTRIENT RELEASE. Soil Biology & Biochemistry 24(10): 1051-1060.

Decomposition and nutrient release patterns of prunings of three woody agroforestry plant species (Acioa barteri, Gliricidia sepium and Leucaena leucocephala), maize (Zea mays) stover and rice (Oryza sativa) straw, were investigated under field conditions in the humid tropics, using litterbags of three mesh sizes (0.5, 2 and 7 mm) which allowed differential access of soil fauna. The decomposition rate constants ranged from 0.01 to 0.26 week-1, decreasing in the following order; Gliricidia prunings > Leucaena prunings > rice straw > maize stover > Acioa prunings. Negative correlations were observed between decomposition rate constants and C:N ratio (P

Tian, G., M. A. Badejo, Okoh, A. I. Ishida, F. Kolawole, G. O. Hayashi, Y. Salako, F. K. (2007). Effects of residue quality and climate on plant residue decomposition and nutrient release along the transect from humid forest to Sahel of West Africa." Biogeochemistry 86(2): 217-229.

Field litterbag studies were conducted in the 2000 rainy season and the 2000/2001 dry season along the transect of West African major agroecological zones (agroeco-zones) to measure the decomposition of, and N and P release from 5 plant residues (leaves of woody species) with increasing quality: Dactyladenia barteri, Pterocarpus santalinoides, Alchornea cordifolia, Senna siamea and Gliricidia sepium. The decomposition rate constant (wk(-1)) ranged from 0.034 (Dactyladenia, subhumid zone) to 0.49 (Gliricidia, humid zone) in the rainy season, and from 0.01 (Dactyladenia, subhumid zone) to 0.235 (Pterocarpus, arid zone) in the dry season. The direct correlation between the decomposition rate of plant residues and their quality was only valid in agroeco-zones where there is not moisture stress. Similarly, the direct correlation between the decomposition rate of plant residues and moisture availability was only valid for plant residues with high quality. The decomposition rate of the low quality plant residue could increase from humid to arid zone in West Africa. In the arid zone, the low quality plant residue could also decompose faster than high quality plant residue. The climate-residue quality interactive effects on plant residue decomposition in West Africa were attributed to the feedback of low quality plant residue's mulching effect, soil fauna and appreciable photodegradation in dry regions. A decomposition equation that could be used to predict the decomposition rate of plant residues with various qualities across agroeco-zones in West Africa was obtained from this study. The equation was expressed as follow: k = 0.122 -0.000747*PRQI(2)-0.0233*PRQI*CI + 0.00337*CI* PRQI(2), in which k is the decomposition rate constant (wk(-1)), PRQI the plant residue quality index, and CI the climate index (ratio of rainfall to sunshine hours cumulative during the entire decomposition). The response of N and P release from plant residues to residue quality and climate was similar to that of residue decomposition. At the late stage of the dry season decomposition, the high C/N and C/P ratio plant residue (Dactyladenia leaves) that immobilized N and P in wet zones showed a release of N and P in the dry zone.

Salako, F. K. and G. Tian (2005). Litter production and soil condition under agroforestry trees in two agroecological zones of southern Nigeria. Journal of Sustainable Agriculture 26(2): 5-21.

Tree species in agroforestry systems contribute to soil improvement through the litter produced on the soil surface and below-ground modification of soil structure by tree roots. Therefore, litter production and soil characteristics under I I tree species were evaluated in the derived savanna (Ibadan) and humid tropical forest (Onne) zones of southern Nigeria between 1998 and 1999 in 7-year old arboreta. In Ibadan, the soil was a gravelly Alfisol, while in Onne it was an Ultisol. The trees were Alchornea cord folia. Baphia pubescens, Calliandra calothyrsus, Dactyladenia barteri, Dialium guineense, Grewia pubescens, Inga edulis, Irvingia gabonensis, Nauclea diderrichii, Ptero-carpus santalinoides and Treculia africana. Forest and natural regrowth (no-tree) plots were included as control. Litter-fall under the trees ranged from 5 to 14 t ha(-1) y(-1) compared to 15 t ha(-1) y(-1) for the forest at Ibadan, while it ranged from 7 to 16 t ha(-1) y(-1) compared to 20 t ha(-1) y(-1) for the forest at Onne. Litter production was high under D. barteri and I. edulis and relatively low under A. cord folia, G. pubescens, I. gabonensis and A santalinoides. There was a more drastic change in soil chemical properties in the Alfisol than the Ultisol, particularly with available P. Soil bulk density and penetrometer resistance were improved by A. cordifolia, C. calothyrsus, D. guineense, G. pubescens and T africana. This study showed that ecological differences resulted in differences in annual litter production for only 33% of the species considered. However, the effects of the trees on soil properties were strongly linked to inherent soil properties.

Salako, F. K. and G. L. Tian (2004). Root distribution of two woody species grown on farmers' fields in the Southern Guinea Savannah Zone of Nigeria. Communications in Soil Science and Plant Analysis 35(17-18): 2577-2592.

Trees play a significant role in improving soils for crop production through root activities. This study was carried out on four farmers' fields in Mokwa, central Nigeria in May 1999 to quantify root distributions of 2-year-old Gliricidia sepium (G. sepium) and Acacia leptocarpa (A. leptocarpa). Root samples were taken up to 300-cm soil depth. Root length, surface area, and volume densities were evaluated by using Delta-T Scan device. Mass density was also evaluated. Root length densities of G. sepium ranged from 0.56-11mm mL(-1) while those of A. leptocarpa ranged from 0.135.93mmmL(-1), declining with soil depth. Potential contribution of roots to soil total porosity was less than 3%. Soil bulk density ranged from 1.28-1.51 g cm(-3) under G. sepium and from 1.29-1.61 g cm(-3) under A. leptocarpa. Although G. sepium had relatively more roots deeper in the soil than A. leptocarpa, both trees demonstrated deep rooting, suggesting that the trees would improve soil productivity if sufficient fallow length were allowed.

Salako, F. K. and G. Tian (2003). Management of a degraded Alfisol for crop production in southwestern Nigeria: Effects of fallow, mounding and nitrogen. Journal of Sustainable Agriculture 22(2): 3-22.

In 1989, 15 fallow species were planted on a degraded Alfisol in southwestern Nigeria, but only Pueraria phaseoloides, Senna siamea, Leucaena leucocephala, Acacia leptocarpa and Acacia auriculiformis survived beyond 1993. After clearing different subplots of the fallowed plots in 1993 and 1995, intercropping of cassava + maize was practiced with level (minimum) and mound tillage. Nitrogen fertilizer, recommended while in the third year, mound tillage with 60 kg N ha(-1) was recommended

Salako, F. K. and G. Tian (2003). Soil water depletion under various leguminous cover crops in the derived savanna of West Africa. Agriculture Ecosystems & Environment 100(2-3): 173-180.

Leguminous cover crops have the potential of making cropping systems in the tropics sustainable if they would not deplete resources such as soil water and nutrients to the detriment of companion crops. Therefore, a study was carried out at Alabata, Ibadan, southwestern Nigeria, to evaluate the effects of leguminous cover crops on soil water suctions in 1993 and 1994 in order to assess the possibility of integrating them into the farming systems of the savanna zone of West Africa. In 1993, 13 leguminous cover crops (Aeschynomene histrix, Centrosema brasilianum, Centrosema pascuorum, Chamaecrista rotundifolia, Cajanus cajan, Crotalaria verrucosa, Crotalaria ochroleuca, Lablab purpureus, Mucuna pruriens, Psophocarpus palustris, Pseudovigna argentea, Pueraria phaseoloides and Stylosanthes hamata) were planted in a randomized complete block design with four replications. Maize and natural fallow (mainly Chromolaena odorata and Imperata cylindrica) were included as comparisons. Only six of the legumes (A. histrix, C. pascuorum, C. cajan, C. ochroleuca, M. pruriens, and P phaseoloides) were included in the measurements in the 1994 new plots. Soil water suctions at various stages of legume growth were measured at daily or weekly intervals (depending on the frequency of rainfall events) using tensiometers installed at 0-15 and 15-30 cm soil depths. Soil water suctions exceeding 10 kPa (theoretical field capacity) were observed mainly between 6 and 12 weeks after planting (WAP), and by 20 WAP when cover crops had matured and rainfall frequency was very low. Soil water suctions were significantly related (r(2) > 0.80) to dry matter between 8 and 10 WAR The studied cover crops were classified in three groups which can be used as a guide for choosing the legumes in tropical farming systems. Soil water depletion was markedly influenced by growth characteristics of legumes and distribution of rainfall during the rainy season. Leguminous cover crops conserved soil water after their growth needs were satisfied.

Salako, F. K., G. Tian and B. T. Kang (2002). Indices of root and canopy growth of leguminous cover crops in the savanna zone of Nigeria. Tropical Grasslands 36(1): 33-46.

This study was carried Out in 1994 in the derived (DS) and northern Guinean savanna (NGS) zones of Nigeria at about 17-18 weeks after planting forage legumes. The forage legumes, which included Cajanus cajan, Crotalaria ochroleuca, Stylosanthes hamata, Centrosema pascuorum, Lablab purpureus, Mucuna pruriens (black and white) and Pueraria phaseoloides, were treatments in the randomised complete block design. Root morphology and length were evaluated for the 2 zones, but light received under canopies, soil temperature and soil water potential were measured only in the DS. Roots on soil profile walls were traced, and in the laboratory, computer software Was used to evaluate root length after scanning. Canopy coverage was evaluated using a light meter. In the DS, the presence of gravel in-the subsoil modified the morphology and distribution of roots even for the same species compared with the root architecture in the NGS zone. A hardpan in the shallow soil layers in the NGS caused a proliferation of roots in the topsoil, and a tendency for increased diameter (visual observation) of the primary roots. Total root length ranged from 834-1861 turn in the DS, and 939-1277 mm in the NGS, and was similar in both locations. Legume canopies intercepted 81-99% of sunlight, suggesting that they had the potential to maximise sunlight for their growth under adequate soil moisture and nutrient in the moist savanna. Legumes such as C. cajan, L. purpureus, M, pruriens and P phaseoloides with potential to grow roots beyond 60 cm depth and which intercepted greater than or equal to95% of incident Sunlight were recommended for sustained growth and rapid regeneration after cutting or browsing. Furthermore, the legumes can be combined with shallow-rooted crops for enhanced crop production in a crop-livestock farming system or in pasture, based oil the differences in their root and canopy growth.

Salako, F. K. and G. Tian (2001). Litter and biomass production from planted and natural fallows on a degraded soil in southwestern Nigeria. Agroforestry Systems 51(3): 239-251.

To rehabilitate a degraded Alfisol at Ibadan, southwestern Nigeria, Senna siamea (non-N-fixing legume tree), Leucaena leucocephala, and Acacia leptocarpa (N-fixing legume trees) were planted in 1989, and Acacia auriculiformis (N-fixing legume tree) in 1990. Pueraria phaseoloides (a cover crop) and natural fallow were included as treatments. Litterfall and climatic variables were measured in 1992/1993 and 1996/1997 while biomass production and nutrient concentrations were measured in 1993 and 1995. Total litter production from the natural and planted fallows was similar, with means ranging from 10.0 (L. leucocephala) to 13.6 t ha(-1) y(-1) (natural fallow) during the 1996/1997 collection. Leaves constituted 73% (L. leucocephala) to 96% (A. auriculiformis) of total litterfall. Acacia auriculiformis grew most quickly but S. siamea produced the highest aboveground biomass which was 127 t ha(-1) accumulated over four years, and 156 t ha(-1) accumulated over six years of establishment. The aboveground biomass of P. phaseoloides and natural fallow was only 6 to 9 t ha(-1) at six years after planting. Nitrogen concentration in the leaves/twigs of was 2.5% for L. leucocephala, and 2% for other planted species and natural fallow. Pueraria phaseoloides had concentrations of P, K, Ca and Mg comparable to levels in the leaves/twigs of the tree species. Through PATH analysis, it was found that maximum temperature and minimum relative humidity had pronounced direct and indirect effects on litterfall. The effects of these climatic variables in triggering litterfall were enhanced by other variables, such as evaporation, wind, radiation, and minimum temperature. Improvement in chemical properties by fallows was observed in the degraded soil

Salako, F. K., S. Hauser, O. Babalola and G. Tian (2001). Improvement of the physical fertility of a degraded Alfisol with planted and natural fallows under humid tropical conditions. Soil Use and Management 17(1): 41-47.

Topsoil (0-15 cm) hulk density, aggregate stability soil dispersibility, water retention and infiltration were measured between 1989 and 1996 on an Alfisol under rehabilitation in southwestern Nigeria. The planted leguminous species were Pueraria phaseoloides, Senna siilnrrir, Leucaena leucocephala,, Acacia leptocarpa and A. auriculiformis. plots with natural fallow and maize/cassava intercropping were included. Level (minimum) and mound tillage with hoes was adopted for the cultivated areas under study after 4 and 6 year fallow periods. Under fallow, the soil bulk density decreased from 1.56 to 1.11 t m(-3). The continuously cropped treatment (level tillage) had significantly higher bulk density than the fallowed subplots after 6 years. Mean soil penetrometer resistance ranged from 75 to 157 kPa for fallowed plots and from 192 to 295 kPa for the continuously cropped (level tillage) subplot. Surface soil water contents were similar for all the treatments during the soil strength measurements. Although soil aggregates were generally of low stability and not well formed, they were improved by fallowing. Soil structural improvement by planted fallows was similar to that by natural fallow, but the trees were more promising for long-term fallow (>6 years) than the herbaceous P. phaseoloides. However, the improvement in soil structure after 4 or 6 rear falloff could not be maintained in subsequent cropping. Furthermore, the significant improvement in soil bulk density caused by A. auriculiformis and natural fallow was more rapidly lost on the cultivated subplots compared with other fallow treatments. Thus, soil structure recovery under a fallow does not imply a sustained improvement when stress is applied to this soil. Post-fallow soil management options such as residue incorporation and tillage to ameliorate compaction or soil strength mill be necessary to enhance the improvements by fallow species.

Tian, G., F. K. Salako and F. Ishida (2001). Replenishment of C, N, and P in a degraded alfisol under humid tropical conditions: Effect of fallow species and litter polyphenols. Soil Science 166(9): 614-621.

The capacity of vegetation fallow to replenish carbon and nutrients in degraded soil is related largely to the nature of the fallow vegetation, particularly the chemical composition. Therefore, a study was conducted at Ibadan, southwestern Nigeria (humid tropics), to look into these relationships using, fallow species with varying chemical compositions. The treatments include three woody species, Senna siamea, Acacia leptocarpa and Leucaena leucocephala, planted in 1989, and the natural shrub Chromolaena odorata. A continuous cropping of maize/cassava was maintained as a control (no fallow). Composite surface soil (0-15 cm) at three distances from a tree hedgerow (0.5, 2.0, and 3.5 m) was sampled in 1996 for the determination of soil C and nutrient stocks. Maize and cassava were planted as a test crop of soil productivity after fallowing. Litterbags were placed to determine the N immobilization during the decomposition of fallow leaves. Soil. organic C (SOC) within 0-15 cm ranged from 19,100 (continuous cropping) to 26,400 kg ha(-1) (Leucaena fallow), whereas total N ranged from 1820 (continuous cropping) to 3110 kg ha(-1) (Leucaena fallow). High polyphenols in fallow leaves favored SOC and N accumulation. The amount of potentially mineralizable N was increased from 41 kg ha(-1) in continuous cropping to 159 under Leucaena fallow and 176 under der Acacia fallow. The percentage increase in mineralizable N stock under fallow was, on average, 5.5 times greater than that in total N, implying that fallow causes change in soil organic matter quality.. The available P (Olsen) was 8.6 kg ha(-1) in the continuous cropping and ranged from 14.1, kg ha(-1). (natural fallow) to 29.2 kg ha(-1) (Leucaena fallow). Greater maize and cassava yields were obtained in the fallow plots than in the control during, the subsequent cropping. The maize grain yield after fallow could be predicted by the potentially mineralizable N in surface soil (0-15 cm). Leucaena and Acacia are promising species for planted fallows for soil regeneration in the humid tropics. The binding of protein by polyphenols during leaf decomposition, as confirmed by higher N immobilization with the increase in leaf polyphenols, could be the main mechanism in the contribution of polyphenols to SOC and N replenish, ment in the degraded soil. The study suggests the possibility of stabilizing C and N in tropical ecosystems by manipulating polyphenols in vegetation.

Tian, G., G. O. Kolawole, F. K. Salako and B. T. Kang (1999). An improved cover crop-fallow system for sustainable management of low activity clay soils of the tropics. Soil Science 164(9): 671-682.

The potential of planted leguminous cover crop fallow as an alternative to the natural regrowth fallow for sustaining the productivity of low activity clay (LAC) soils in the tropics as the fallow period shortens was tested at Ibadan in the forest-savanna zone of southwestern Nigeria. The study, initiated in 1990, compared an improved system (cover crop-fallow) and a traditional system (natural fallow), with the aim of developing an improved cover crop-fallow system for sustainable management of LAC soils of the tropics. Pueuraria phaseoloides, an herbaceous, N-fixing, perennial legume with a slow initial growth habit, was selected as a test cover crop. Pueraria was sown with a maize-cassava intercrop at the same season. In a 2-year cycle, 1 year of cropping was followed by 1 year fallow with pueraria fdr the cover crop-fallow system or with natural regrowth (mainly Chromolaena odorata) for the natural fallow system. Maize-cassava intercropping without a fallow period (continuous cropping) was included as a control. No fertilizer was applied throughout the experimental period. Pueraria produced 253 kg N ha(-1) after the fallow period, compared with 109 kg N ha(-1) for chromolaena; pueraria was also better in recycling P (11 kg P ha(-1)) than was chromolaena (9 kg P ha(-1)), Natural fallow for 1 year increased the maize yield from 75 to 350% from 1992 to 1996, and the cassava yield from 9 to 130% compared with continuous cropping. Cover crop-fallow resulted in a 22 to 72% higher maize yield than the natural fallow from 1992 to 1996. Although in 1992 and 1994 cassava tuber yield was lower with the cover crop-fallow than with the natural fallow, with better pueraria husbandry in 1996, cover crop-fallow increased the cassava tuber yield by 41%. With residue burning, the N balance was 27 kg N ha(-1) yr(-1) for the pueraria cover crop-fallow system and -15 kg N ha(-1) yr(-1) for the chromolaena natural fallow system. Cover crop-fallow maintained soil organic carbon status better than the natural fallow. Integration of a pueraria legume cover crop did not affect soil pH. Results indicate cover crop-fallow with pueraria could be a better alternative to traditional natural fallow under shortened fallow periods for raising or maintaining productivity of LAC soils of the humid tropics

Salako, F. K., G. Kirchhof and G. Tian (2006). Management of a previously eroded tropical Alfisol with herbaceous legumes: Soil loss and physical properties under mound tillage. Soil & Tillage Research 89(2): 185-195.

A study was carried out on a previously eroded Oxic Paleustalf in Ibadan, southwestern Nigeria to determine the extent of soil degradation under mound tillage with some herbaceous legumes and residue management methods. A series of factorial experiments was carried out on 12 existing runoff plots. The study commenced in 1996 after a 5-year natural fallow. Mound tillage was introduced in 1997 till 1999. The legumes - Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides - were intercropped with maize in 1996 and 1998 while yam was planted alone in 1997 and 1999. This paper covers 1997-1999. At the end of each year, residues were either burned or mulched on respective plots. Soil loss, runoff, variations in mound height, bulk density, soil water retention and sorptivity were measured. Cumulative runoff was similar among interactions of legume and residue management in 1997 (57-151 mm) and 1999 (206-397 mm). However, in 1998, cumulative runoff of 95 mm observed for Mucuna-burned residue was significantly greater than the 46 mm observed for cowpea-burned residue and the 39-51 mm observed for mulched residues of cowpea, Mucuna and Pueraria. Cumulative soil loss of 7.6 Mg ha(-1) observed for Mucuna-burned residue in 1997 was significantly greater than those for Pueraria-mulched (0.9 Mg ha(-1)) and Mucuna-mulched (1.4 Mg ha(-1)) residues whereas in 1999 it was similar to soil loss from cowpea treatments and Pueraria-burned residue (2.3-5.3 Mg ha(-1)). There were no significant differences in soil loss in 1998 (1-3.2 Mg ha(-1)) whereas Mucuna-burned residue had a greater soil loss (28.6 Mg ha(-1)) than mulched cowpea (6.9 Mg ha(-1)) and Pueraria (5.4 Ms ha(-1)). Mound heights (23 cm average) decreased non-linearly with cumulative rainfall. A cumulative rainfall of 500 mm removed 0.3-2.3 cm of soil from mounds in 1997, 3.5-6.9 cm in 1998 and 2.3-4.6 cm in 1999, indicating that (detached but less transported) soil from mounds was far higher than observed soil loss in each year. Soil water retention was improved at potentials ranging from -1 to -1500 kPa by Mucuna-mulched residue compared to the various burned-residue treatments. Also, mound sorptivity at -1 cm water head (14.3 cm h(-1/2)) was higher than furrow sorptivity (8.5 cm h(-1/2)), indicating differences in hydraulic characteristics between mound and furrow. Pueraria-mulched residues for mounds had the highest sorptivity of 17.24 cm h(-1/2), whereas the least value of 6.96 cm h(-1/2) was observed in furrow of Mucuna-burned residue. Pueraria phas eoloides was considered the best option for soil conservation on the previously eroded soil, cultivated with mound tillage.

Salako, F. K., G. Tian, G. Kirchhof and G. E. Akinbola (2006). Soil particles in agricultural landscapes of a derived savanna in southwestern Nigeria and implications for selected soil properties. Geoderma 137(1-2): 90-99.

The vast area of savanna ecology in Afiica plays a significant role in food production, making a study of soils in this zone very important. Therefore, soil physical and chemical properties of 14 soil profiles were studied in a derived savanna zone of southwestern Nigeria on 2 toposequences at 2 locations (Ibadan and Alabata), which were 20 kin apart. Six soil profiles were studied at Ibadan while 8 were studied at Alabata. Morphological descriptions of profiles were carried out. Data collected included particle size distribution, bulk density, clay dispersion, water retention characteristics, pH, organic carbon, exchangeable K, Ca, Mg and available P. Soil profiles along the toposequences were well-developed with depths exceeding 180 cm, except for one profile at the lower slope position where an indurated plinthic layer was found at 68 cm depth. The horizons were easily distinguished with color, texture and consistency. Total sand, with the main component being coarse sand, decreased with depth from 813 to 502 g kg(-1) at Ibadan and from 824 to 635 g kg(-1) at Alabata. The clay content increased with depth from 54 to 3 5 6 g kg(-1) at Ibadan and from 63 to 279 g kg(-1) at Alabata. Gravel concentration was highest for soil horizons found between 20 and 102 cm depth. Also, bulk density increased with soil depth from 1.35 to 1.51 g cm(-3) at Ibadan and from 1.38 to 1.64 g cm(-3) at Alabata, indicating that subsoil horizons were more compact due to higher clay and gravel contents, and sticky consistency. The A horizon had a significantly higher water content at water potentials > 2 kPa while the subsoils had higher water content at

Tian, G., G. O. Kolawole, B. T. Kang and G. Kirchhof (2000). Nitrogen fertilizer replacement indexes of legume cover crops in the derived savanna of West Africa. Plant and Soil 224(2): 287-296.

Legume cover crops are a potential means for overcoming N depletion in the derived savanna of West Africa. A 3-year trial was, therefore, conducted near Ibadan, southwestern Nigeria to measure the N contribution of 13 legume cover crops as compared to urea -N, using a N fertilizer replacement index for a maize test crop. Two series of trials involved the following legume cover crop species: Aeschynomene histrix, Centrosema brasilianum, Centrosema pascuorum, Chamaecrista rotundifolia, Cajanus cajan, Crotalaria verrucosa, Crotalaria ochroleuca, Lablab purpureus, Mucuna pruriens, Psophocarpus palustris, Pseudovigna argentea, Pueraria phaseoloides and Stylosanthes hamata. Trials were undertaken using a complete block design. Cover crops were planted in 1994 (Series 1) and 1995 (Series 2) in separate sites and each series was subsequently slashed and planted for one season with maize (Zea mays) in 1995 and 1996. At the 50% flowering stage, N concentration of above-ground vegetation of cover crops ranged from 21 to 38 g N kg(-1). Nitrogen accumulated by 4.5-month old cover crops ranged from 14 to 240 kg N ha(-1), depending on species and year. Cover crops increased grain yield of the subsequent maize crop by 25-136% over the control without N application. Nitrogen uptake by the maize crop was higher following cover crops than after maize or natural grass. The N fertilizer replacement index of cover crops for maize ranged from 11 (A. histrix) to 96 kg N ha(-1) (C. cajan) in Series 2. Perennial ( C. brasilianum, S. hamata, C. cajan, P. phaseoloides and C. verrucosa) and annual (C. rotundifolia, M. pruriens, C. ochroleuca and L. purpureus) species could potentially save 50 to 100 kg N ha(-1) for maize crops. The cover crops accumulated more N in the wetter than in the drier year. However, the N fertilizer replacement index was higher for subsequent maize grown in the drier year. The cover crop-N recovery in maize was also higher than the urea-N uptake in the drier year. The N fertilizer replacement indexes can be predicted using the above-ground biomass amount of cover crops at 20 weeks after planting (drier year) or the N concentration at that stage (wetter year).

Huang, CY, Jien, SH, Chen, TH, Tian, G and Chiu, CY. 2014. Soluble organic C and N and their relationships with soil organic C and N and microbial characteristics in moso bamboo (Phyllostachys edulis) plantations along an elevation gradient in Central Taiwan. Journal of Soils and Sediments 14: 1061–1070.

Purpose: Moso bamboo (Phyllostachys edulis), an important economic crop, is distributed from low- to medium-elevation mountains in Taiwan. Bamboo is a fast-growing herbaceous species with an extensive rhizome structure. With the hypothesis that the characteristics of soil organic matter and microbes might change after long-term bamboo plantation, we investigated different fractions of organic C and N as well as soil microbial biomass and activities in 5 moso bamboo plantations along an elevation gradient in Central Taiwan. Materials and methods: Five soil samples (top 10 cm soil) were collected from each bamboo plantation (600, 800, 1000, 1200 and 1400 m asl) in January 2011. Soil was processed and analyzed for soil total C and N content, biological available C, potential mineralizable N, and soil microbial biomass and soil respiration (CO2). Two extraction methods (2 M KCl and hot-water extraction) were used to estimate soil soluble organic C and N (SbOC and SbON) and soil inorganic N (NH4+ and NO3?) concentrations to evaluate the relationship with soil organic matter and microbe characteristics in bamboo plantations. Results and discussion: Soil total C and N contents as well as soil microbial biomass and soil respiration (CO2) of the bamboo plantations increased along the elevation gradient. Temperature changes along elevation contributed to such variations observed among the selected bamboo plantations. SbON in hot-water extracts was highest in the 1200-m plantation, then the 1400-m plantation, and lowest in the low-elevation plantations (600, 800 and 1000 m). However, SbON in 2 M KCl extracts did not differ by elevation. SbON was strongly correlated with soil total N in both 2 M KCl and hot-water extracts but only SbON in hot water extracts was strongly correlated with microbial biomass N and potential mineralizable N. SbOC was strongly correlated with soil total C content, microbial biomass C, and biological available C in both 2 M KCl and hot-water extracts. Conclusions: Soil total C and N, SbOC and SbON and microbial biomass characteristics increased in the moso bamboo plantations with increasing elevation. No altitudinal difference in specific soil respiration (CO2) rate suggested that the enhanced potential mineralizable N and soil respiration (CO2) in the high-elevation plantations was associated with increased microbial biomass rather than microbial activities.

Lukicheva I, Pagilla K, Tian G, Cox A and Granato T. 2014. Enhanced stabilization of digested sludge during long-term storage in anaerobic lagoons. Water Environment Research 86: 291-295.

The goal of this work was to study changes in anaerobically stored digested sludge under different lengths of storage time to evaluate the quality of final product biosolids. The analyses of collected data suggest the organic matter degradation occurrence in the anaerobic environment of the lagoon approximately within the first year. After that, the degradation becomes very slow, which is likely caused by unfavorable environmental conditions. The performance of lagoon aging of digested sludge was also compared to the performance of lagoon aging of anaerobically digested and dewatered sludge. It was concluded that both of these processes result in biosolids of comparative quality and that the former provides more economical solution to biosolids handling by eliminating the need for mechanical dewatering.

Chen, JS. Chung, TL. Tian, GL. Chiu, CY. 2013. Characterization of soil organic matter in perhumid natural cypress forest: comparison of humification in different particle-size fractions. BOTANICAL STUDIES. 54, 1-9.

The Chamaecyparis forest is a valuable natural resource in eastern Asia. The characteristics of soil humic substances and the influence of environmental factors in natural Chamaecyparis forests in subtropical mountain regions are poorly understood. The study site of a perhumid Chamaecyparis forest is in the Yuanyang Lake Preserved Area in northcentral Taiwan. We collected samples from organic horizons (Oi, Oe and Oa) and from the surface horizon (O/A horizon) at the summit, footslope and lakeshore to characterize the composition of the soil organic matter. Samples of organic horizons were dried and ground, and those of the O/A horizon were passed through wet sieving for different particle-size fractions before analysis. The C chemical structure in the samples was determined with CP/MAS C-13 NMR spectra. Results: The ratios of alkyl-C/O-alkyl-C and aromaticity increased with decomposition of litter from the Oi, Oe, to Oa horizon. The ratio of alkyl-C/O-alkyl-C also increased from coarse (> 250 mu m) to very fine (

Oladeji, OO. Tian, GL . Cox, AE. Granato, TC. O'Connor, C. Abedin, Z. Pietz, RI. 2013. Effect of Long-Term Application of Biosolids for Mine Land Reclamation on Groundwater Chemistry: Nutrients and Other Selected Qualities. JOURNAL OF ENVIRONMENTAL QUALITY. 41, 94-102.

Leaching of nitrogen (N) and phosphorus (P) to groundwater can limit the land application of fertilizer, biosolids, and other soil amendments. Groundwater quality monitoring data collected over a 34-yr period at a 1790-ha site in Fulton County, Illinois, where strip-mined land was reclaimed with biosolids, were used to evaluate long-term impacts of biosolids on groundwater N, P, and other parameters. Seven strip-mined fields repeatedly treated with biosolids at 801 to 1815 Mg ha(-1) cumulative rate (equivalent to 24-55 dry Mg ha(-1) yr(-1)) between 1972 and 2004 were compared with another seven fields treated annually with chemical fertilizer at agronomic rates. Groundwater from wells installed in each of the fields and two public wells that served as background (reference) were sampled for 35 yr, monthly between 1972 and 1986 and quarterly between 1987 and 2006. Data show greater chloride (Cl-), sulfate (SO42-) and electrical conductivity (EC) of groundwater from wells in biosolids fields than those in fertilizer fields. Also, groundwater nitrate N (NO3-N) concentrations were greater in biosolids-amended fields than in fertilizer fields, but below regulatory limit of 10 mg (L-1) in Illinois Part 620 regulation. Conversely, groundwater P concentrations were consistently lower in biosolids than in chemical fertilizer wells throughout the 35-yr monitoring period. The study demonstrates that the repeated application of biosolids, even at higher than agronomic rate, would cause only minor nitrate increase and no P increase in groundwater.

Thangarajan, R. Bolan, NS. Tian, GL. Naidu, R. Kunhikrishnan, A. 2013. Role of organic amendment application on greenhouse gas emission from soil. SCIENCE OF THE TOTAL ENVIRONMENT. 465, 72-96.

Globally, substantial quantities of organic amendments (OAs) such as plant residues (3.8 x 10(9) Mg/yr), biosolids (10 x 10(7) Mg/yr), and animal manures (7 x 10(9) Mg/yr) are produced. Recycling these OAs in agriculture possesses several advantages such as improving plant growth, yield, soil carbon content, and microbial biomass and activity. Nevertheless, OA applications hold some disadvantages such as nutrient eutrophication and greenhouse gas (GHG) emission. Agriculture sector plays a vital role in GHG emission (carbon dioxide-CO2, methane-CH4, and nitrous oxide-N2O). Though CH4 and N2O are emitted in less quantity than CO2, they are 21 and 310 times more powerful in global warming potential, respectively. Although there have been reviews on the role of mineral fertilizer application on GHG emission, there has been no comprehensive review on the effect of OA application on GHG emission in agricultural soils. The review starts with the quantification of various OAs used in agriculture that include manures, biosolids, and crop residues along with their role in improving soil health. Then, it discusses four major OA induced-GHG emission processes (i.e., priming effect methanogenesis, nitrification, and denitrification) by highlighting the impact of OA application on GHG emission from soil. For example, globally 10 x 10(7) Mg biosolids are produced annually which can result in the potential emission of 530 Gg of CH4 and 60 Gg of N2O. The article then aims to highlight the soil, climatic, and OA factors affecting OA induced-GHG emission and the management practices to mitigate the emission. This review emphasizes the future research needs in relation to nitrogen and carbon dynamics in soil to broaden the use of OAs in agriculture to maintain soil health with minimum impact on GHG emission from agriculture

Tian, G. Franzluebbers, AJ. Granato, TC. Cox, AE. O'Connor, C. 2013. Stability of soil organic matter under long-term biosolids application. APPLIED SOIL ECOLOGY. 64, 223-227.

Little is know on the impact of biosolids application on soil organic matter (SUM) stability, which contributes to soil C sequestration. Soil samples were collected in 2006 at plow layer from fields that received liquid and dry municipal biosolids application from 1972 to 2004 at the cumulative rate of 1416 Mg ha(-1) in mined soil and 1072 Mg ha(-1) in nonmined soil and control fields that received chemical fertilizer at Fulton County, western Illinois. The biosolids application increased the soil microbial biomass C (SMBC) by 5-fold in mined soil and 4-fold in nonmined soil. The biosolids-amended soils showed a high amount of basal respiration and N mineralization, but low metabolic quotient, and low rate of organic C and organic N mineralization. There was a remarkable increase in mineral-associated organic C from 6.9 g kg(-1) (fertilizer control) to 26.6 g kg(-1) (biosolids-amended) in mined soil and from 8.9 g kg(-1) (fertilizer control) to 23.1 g kg(-1) (biosolids-amended) in nonmined soil. The amorphous Fe and Al, which can improve SUM stability, were increased by 2-7 folds by the long-term biosolids application. It is evident from this study that the biosolids-modified SUM resists to decomposition more than that in the fertilizer treatment, thus long-term biosolids application could increase SUM stability

Zhai, WJ. Moschandreas, DJ. Tian, GL. Venkatesan, D. Noll, KE. 2013. Degradation Rate Model Formulation to Estimate Soil Carbon Sequestration from Repeated Biosolids Application. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 78, 1, 238-247.

Land application of biosolids is a process that increases the amount of soil C sequestration and may produce C credits in accordance with the definition of United Nations Climate Change Convention. A dynamic degradation rate model (DRM) provides insights on C sequestration due to microbial biomass, soil organic carbon (SOC), CO2 emission rates, residence time of sequestered C, and biomass to biosolids ratios. We employed a 34-yr biosolids application database from the literature to determine the amount of C sequestered in 41 strip-mined Illinois fields. This database is used to formulate the DRM using curve fitting techniques. Degradation rate model applications identify two SOC phases in soil. Soil organic C gain in Phase 1 (first 10 yr) is primarily due to biosolids application while in Phase 2, SOC gain is due to biomass or C sequestration. Carbon sequestration changes with time relate to variations in biosolids application amounts (10 and 18 Mg ha(-1) yr(-1)), different degradation rate constants (0.04-0.16 yr(-1)), and biomass yields (35-40%). Additionally, the degradation rate constant is correlated positively with the C application rate for a period of 34 yr. Based on the 34-yr database, the DRM simulates the process that decomposes SOC produced by biosolids application into C in biosolids that have not been degraded and C in biomass produced during the microbial degradation process. The DRM quantifies the biosolids degradation rate constant and biomass yield, and provides an easy quantitative method for evaluating C credits from biosolids added to soil.

Chung TL, Chen JS, Chiu CY and Tian G. 2012. 13C-NMR spectroscopy studies of humic substances in subtropical perhumid montane forest soil. Journal of Forest Research 17: 458-467.

We investigated soil organic matter in a forest of natural Hinoki cypress (Chamaecyparis obtusa) under perhumid weather conditions in north central Taiwan. Humic substances along the transect from the summit and footslope to lakeshore were characterized by use of solid-state cross-polarization, magic-angle-spinning 13C nuclear magnetic resonance spectroscopy (CP/MAS 13C-NMR). The major components of soil organic carbon in whole soil and humic substances were alkyl-C, O-alkyl-C, and di-O-alkyl-C, ranging from 60.6% to 80.7%, then aromatic-C, 7.5% to 9.8%. The degree of humification of soil organic matter, both O-alkyl-C/alkyl-C ratio and aromaticity, decreased slightly from the summit to lakeshore. The content of functional groups of polar and acidic groups, including O-alkyl-C, di-O-alkyl-C, and carboxyl-C, corresponded with the topographical effect, increasing slightly from the summit to lakeshore. However, the relatively low degree of humification in soils of this perhumid forest and low aromaticity were due to high precipitation and acidity, which appeared to hinder organic matter decomposition with topography change.

Lukicheva I, Tian G, Cox A, Granato TC and Pagilla K. 2012. Anaerobic and aerobic transformations affecting stability of dewatered sludge during long-term storage in a lagoon. Water Environment Research 84: 17-24.

The goal of this work was to study long-term behavior of anaerobically digested and dewatered sludge (biosolids) in a lagoon under anaerobic and aerobic conditions to determine the stability of the final product as an indicator of its odor potential. Field lagoons were sampled to estimate spatial and temporal variations in the physical-chemical properties and biological stability characteristics such as volatile solids content, accumulated oxygen uptake, and soluble protein content and odorous compound assessment. The analyses of collected data suggest that the surface layer of the lagoon (depth of above 0.15 m) undergoes long-term aerobic oxidation resulting in a higher degree of stabilization in the final product. The subsurface layers (depth 0.15 m below the surface and deeper) are subjected to an anaerobic environment where the conditions favor the initial rapid organic matter degradation within approximately the first year, followed by slow degradation.

Oladeji, OO. Tian, GL. Cox, AE . Granato, TC. Pietz, RI. Carlson, CR. Abedin, Z. 2012. Effects of Long-Term Application of Biosolids for Mine Land Reclamation on Groundwater Chemistry: Trace Metals. JOURNAL OF ENVIRONMENTAL QUALITY. 41, 1445-1451.

Data collected for 35 yr from a 1790-ha strip mine reclamation site in Fulton County, Illinois, where biosolids were applied from 1972 to 2004, were used to evaluate the impacts of long-term biosolids application on metal concentrations in groundwater. Groundwater samples were collected between 1972 and 2006 from wells installed in seven strip-mined fields treated with biosolids at cumulative loading rates of 801 to 1815 dry Mg ha(-1) and from another seven fields (also strip mined) treated with mineral fertilizer. Samples were collected monthly between 1972 and 1986 and quarterly between 1987 and 2004 and were analyzed for total metals. The concentrations of metals in groundwater were generally below regulatory limits. Lead, Cd, Cu, Cr, Ni, and Hg concentrations in groundwater were similar for the biosolids-amended and fertilizer-treated sites across all sampling intervals. Zinc concentration was increased by biosolids application only for samples collected before the 1993 promulgation of the USEPA 40 CFR Part 503 rule. Iron and Mn were the only metals that were consistently increased aft er biosolids application; however, Mn concentrations did not exceed the 10 mg L-1 regulatory limits. Zinc, Cu, Cd, Pb, Fe, Al, and Mn concentrations in groundwater decreased with time, coupled with the change from pre-part 503 to post-Part 503 biosolids. The concentrations of other metals, including Ni, Cr, and Hg, did not increase in groundwater with the prolonged biosolids application. The study suggests that the long-term application of biosolids at high loading rates does not result in trace metal pollution of groundwater.

Chiu CY and Tian G. 2011. Chemical structure of humic acids in biosolids-amended soils as revealed by NMR spectroscopy. Applied Soil Ecology 49: 76– 80.

We used NMR spectroscopy to characterize humid acids extracted from soils that had received long-term application of 2 levels of biosolids to evaluate the soil organic matter (SOM) stability in biosolids-amended soils. The study also quantified fulvic acids (FAs), humic acids (HAs) and Fe/Al oxides. The soils were collected in 2004 from 7 fields, in Fulton County, southwestern Illinois, which received biosolids at a cumulative rate of 0, 554 and 1,066 Mg ha-1. The application of biosolids increased both FA and HA contents, but biosolids-amended soil and control soil did not differ in FA/HA ratio. Biosolids application had no effect on water-soluble organic carbon content. Biosolids application increased the presence of Fe/Al in the SOM complex and lowered its C/Fe and C/Al ratios. 13C NMR spectra showed increased alkyl C and decreased aromatic C content in soil HAs with the application of biosolids, and the extent of such changes was higher with high than low biosolids treatment. Under biosolids application, the soil HAs’ C structure shifts from O-alkyl-dominant to alkyl-dominant. Biosolids application does not decrease SOM stability but rather increases the stability of soil humic substances.

Adeoye, G. O., G. Tian, E. P. Opuokpo and D. K. A. Shodeke (2010). Greenhouse monitored growth characteristics and biomass distribution of four legumes and a grass on some acidic non acidic alfisols of southern Nigeria. Nigerian Journal of Soil Science 20(1): 161-167.

Growth characteristics of four herbaceous legumes ( Mucuna pruriens, Lablab purpureus, Pueraria phaceoloides and Centrosema bracillanum) and a grass ( Penicetum purpureum) were evaluated on acid and non-acid soils of southern Nigeria in a greenhouse potted experiment. Shoot biomass, root distribution and nodulation determined at four months after planting showed differences between species. The nodule number and nodule dry weight of legumes grown on non-acid soil averaged 51% and 52% above those on acid soil respectively. Besides, the root diameter was 17% larger in non-acid soil than on acid soil. Whereas the average of total root length on acid soil was 37% more than in the non-acid.

Tian, G., T. C. Granato, A. E. Cox, R. I. Pietz, C. R. Carlson, Jr. and Z. Abedin (2009). Soil Carbon Sequestration Resulting from Long-Term Application of Biosolids for Land Reclamation. Journal of Environmental Quality 38(1): 61-74.

Investigations on the impact of application of biosolids for land reclamation on C sequestration in soil were conducted at Fulton County, Illinois, where 41 fields (3.6-66 ha) received biosolids at a cumulative loading rate from 455 to 1654 dry Mg ha(-1) for 8 to 23 yr in rotation from 1972 to 2004. The fields were cropped with corn, wheat, and sorghum and also with soybean and grass or fallowed. Soil organic carbon (SOC) increased rapidly with the application of biosolids, whereas it fluctuated slightly in fertilizer controls. The peak SOC in the 0- to 15-cm depth of biosolids-amended fields ranged from 4 to 7% and was greater at higher rates of biosolids. In fields where biosolids application ceased for 22 yr, SOC was still much higher than the initial levels. Over the 34-yr reclamation, the mean net soil C sequestration was 1.73 (0-54-3-05) Mg C ha(-1) yr(-1) in biosolids-amended fields as compared with -0.07 to 0.17 Mg C ha(-1) yr(-1) in fertilizer controls, demonstrating a high potential of soil C sequestration by the land application of biosolids. Soil C sequestration was significantly correlated with the biosolids application rate, and the equation can be expressed as y = 0.064 x -0.11, in which y is the annual net soil C sequestration (Mg C ha(-1) yr(-1)), and x is annual biosolids application in dry weight (Mg ha(-1) yr(-1)). Our results indicate that biosolids applications can turn Midwest Corn Belt soils from current C-neutral to C-sink. A method for calculating SOC stock tinder conditions in which surface soil layer depth and mass changes is also described.

Okoh, A. I. and G. Tian (2008). Dynamics of culturable soil microbial communities during decomposition of some agroforestry species in a semi arid and arid tropical agroecozones of West Africa. African Journal of Biotechnology 7(20): 3693-3699.

Field litterbag studies were conducted during the dry season between years 2000 and 2001 in typical semi-arid and arid agroecozones of West Africa to measure the dynamics of culturable bacterial and fungal communities in the topsoils. Five different agroforestry leaf litters namely Dactyladenia, Pterocarpus, Alchonea, Senna, and Gliricidia species were decomposed, and their effects on soil microflora were studied. Bacterial densities in all the studied plots of the two agroecozones varied from the order of 10(8) to 10(10) cfu/g, while fungal densities ranged in the order of 10(3) and 10(4) cfu/g. Ecological zones impacted significantly (P

Tian, G., T. C. Granato, Dinelli, F. D., Cox, A. E. (2008). Effectiveness of biosolids in enhancing soil microbial populations and N mineralization in golf course putting greens. Applied Soil Ecology 40(2): 381-386.

In an effort to generate more information on the use of biosolids in the turf industry, a study was conducted to compare the effectiveness of biosolids with recommended organic sources in enhancing soil microbial populations and N availability in putting green sand rootzones. The treatments included four types of rootzones as follows: sand (control), sand mixed with Dakota reed-sedge peat (10%, v/v), sand mixed with yard-waste compost (10%, v/v), and sand mixed with biosolids (10%, v/v), which were established at the North Shore Country Club golf course, Glenview, IL, USA in 1997. All plots received the same fertilizers mainly in organic forms at 100 kg N ha(-1) year(-1). creeping bentgrass (Agrostis palustris) turf was established, and was managed as a practice putting green. Soil microbial biomass in the rootzone (0-30 cm) was higher either under compost (fall 2004 and summer 2005) or biosolids (summer 2003) than other treatments. Rootzone ammonium oxidizer populations were higher with biosolids (5400 g(-1) soil) than peat (1200 g(-1) soil) and compost (500 g-1 soil) amendment and in control (400 g(-1) soil) in summer 2003. The nitrite oxidizer populations were higher with biosolids (24000 g(-1) soil) than compost (8300 g(-1) soil) and peat (4700 g(-1) soil) amendment and in control (3700 g(-1) soil) in summer 2005. Soil potentially mineralizable N, also being lowest in control, was higher in the biosolids-amended than compost- and peat-amended rootzones. In most seasons, the nitrate concentrations in biosolids rootzone (3.16-19.3 mg kg(-1)) were higher than in compost (2.79-17.7 mg kg(-1)), peat (1.83-14.4 mg kg(-1)), and control rootzone (0.81-15.2 mg kg(-1)). The study indicates that while compost could restore soil microbial biomass better than peat, biosolids could maintain greater N supply than peat and compost.

Ogunwole, J.O., A.B. Lawal, J.D. Olarewaju, K. Audu, D.I. Adekpe, O.O. Ugbabe, D.T. Yaro and E.Y. Oyinlola 2006. Integrated soil water and nutrient management for late season crop production systems in the Nigerian Savanna. Journal of Agronomy 5, 314-320.

The agronomic, ecological and economic aspects of some organic waste application along with water harvesting techniques on the performance of off-season tomatoes and late season roselle and cotton in a dry land savanna agroecosystem were investigated. Different organic materials were applied as amendments to soil for tomoto production under soil residual moisture condition. In addition, roselle and cotton were cultivated using tied ridge moisture conservation techniques and different nutrient sources in a savanna Alfisol at Samaru, Nigeria. The use of organic amendments produced similar fruit yield with those tomato receiving mineral fertilizer amendments. Organic amendments produced tomato fruits with 70 to 80% marketable yield while 84% of fruit yield were marketable under mineral fertilizer application. Net income from sales of tomato under organic amendments showed that they could produce comparable profit margin with those produced from mineral fertilizers. Trace and heavy metal accumulation in tomato leaves were generally within critical concentrations of those elements in plants. The tied ridge technique significantly increased cotton yield by 54% when compared with the conventional open ridge technique. In addition, cow dung amendment produced 42% more seed cotton than the recommended practice of using mineral fertilizer. Cost-benefit ratio revealed that the use of organic waste material in cotton production resulted in a positive net returns. Hence application of organic waste to soils is potentially an important means of recovery of soil organic matter and an essential disposal method

Raji, B.A., J.O. Ogunwole, 2006. Potential of soil carbon sequestration under various landuse in the subhumid and semi arid Savanna of Nigeria: lesson from long term experiments. International Journal of Soil Science 1: 33-43

[The objective of this research is to use the opportunity of the long term cowdung (D), nitrogen (N), phosphorus (P) & potassium (K) trial at Samaru and the improved pasture trial at Shika both in Zaria and the sand dune stabilization trial at Gidan Kaura near Illela in NW Nigeria to provide reliable estimates of the long term soil C turnover in the semi-arid and sub-humid savannas of Nigeria and by extension, West Africa. After 45 years of the DNPK treatments, Soil organic carbon (SOC) content in the unamended soil (control) was still on a slight increase, as represented b an increase of 1.81 t C ha-1 or 10 g C m-2 yr-1between 1977 & 1995. In the same period of 45 years, the use of continuous NPK application resulted in only slight increase in SOC (3%) over the unamended soil while manure with NPK gave 115% more SOC. The use of NPK between 1977 & 1995, a period of 18 years, improved SOC conent from 4.95 to 7.30 t C ha-1 giving a rate of 13 g C m-2 yr-1. This rate is about 50% less the rate using manure aone and 75% less using manure with NPK. After 6 years of natural fallow, the unamended soils experienced a slight decrease in SOC content from 7.04 to 6.83 t C ha-1 representing about 3% reduction. Generally, the rate of SOC sequestration during the fallow period is approximately 400% more than the rates under continuous cultivation. The rate of carbon sequestration for plots receiving manure during cultivation is 24 g C m-2 yr-1 and this increased to 108g C m-2 yr-1 during the fallow period…….

Ogunwole, J.O. 2005. Changes in an alfisol under long-term application of manure and inorganic fertilizer. Soil Use and Management 21, 260-261.

Changes in surface soil properties of a Savanna Alfisol under cultivation with application of manure and inorganic NPK fertilizer were evaluated after 45 years of annual cropping. Soils from treatments with fertilizer only, fertilizer in combination with farmyard manure (FYM) at both high and low rates were compared to soil from a control receiving neither fertilizer nor manure. The high rate of FYM and fertilizer significantly improved soil aggregation, increased C, N, and P status, while reducing soil penetration resistance. The results showed that there is a need to use both manure and inorganic fertilizer to maintain soil fertility in savanna soils under continuous cultivation

Ogunwole, J.O. and Ogunleye, P.O. 2005. Influence of long term application of organic and mineral fertilizers on quality of a savanna Alfisol. Journal of Sustainable Agriculture (New York: Food Product Press of the Haworth Press Inc.) 26(3):5-14

The soils of the West African Savanna are low in physical and chemical productivity. One conventional method of improving productivity of these soils is through the application of organic materials either as supplement or an alternative to mineral fertilizers. In terms of physical and fertility properties, the agricultural value of this practice is unquestionable. However, its influence on trace and heavy metal accumulation in the soil needs to be determined for the practice to be considered sustainable. This study investigated the occurrence of trace and heavy metals in the top soil of an Alfisol under 45 years of application of cow-dung (D), nitrogen (N), phosphorus (P) and potassium (K) at Samaru, Nigeria. Results showed that soil texture ranging from sandy loam to loam. Higher soil surface bulk density were observed for D, DN, K and NPK treatments, however, the DNPK treatment recorded a lower soil surface bulk density averaging 1.44 Mg m-3. Treatments with cow-dung generally recorded a higher saturated hydraulic conductivity. None of the trace and heavy metals analyzed attained values that indicate serious contamination (i.e. intervention values) except for chromium (Cr), whose values indicate heavy contamination in soils of DN and DP treatments, thus reducing their quality. On the basis of soil quality and the physical properties considered, the long term DNPK treatment provided the most suitable agricultural practice. Since it recorded lower values of trace and heavy metals relative to the other treatments

Odunze, A.C., S.A. Tarawali, N. C. de Haan, E.N.O. Iwuafor, P.D. Katung, G.E. Akoueguon, A.F. Amadji, R. Schultze-Kraft, T.K. Atala, A. Adamu, A.O. Babalola, J.O. Ogunwole, A. Alimi, S.U. Ewansiha and S.A. Adediran, 2004. Grain legumes for soil productivity improvement in the Northern Guinea Savanna of Nigeria. Food, Agriculture and Environment 2 (2): 218-226

The Nigerian Savanna zone is currently witnessing increased intensities of crop and livestock production activities that are resulting in increased soil erosion, de-vegetation of the land area, and desert encroachment especially during the dry season. These may have led to the presence of several overgrazed and bare ground areas that is highly susceptible to soil erosion. At harvest, both crop and residues are removed from the field, thus limiting potential nutrient recycling between crop and soil, and further impoverishing the nutrient status of the soils. The Nigerian Savanna zone soils therefore have low total nitrogen, organic carbon, available phosphorus and cation exchange capacity and, are therefore said to have poor fertility status and very low buffering capacity. The present study aimed to determine effects of grain legumes on soil potential in the arid systems was therefore imposed on soils of Zaria area. Results showed that sole legumes and legumes/maize treatments generally resulted in higher organic carbon contribution than sole maize treatment, suggesting that sole maize grown continuously on one farm for years could degrade the organic carbon content of the soil. Also, the sole legume and legume/maize treatments resulted in improvement in soil nitrogen in the range of 65.6 to 84.8%, while nitrogen under sole maize resulted in only 5.9% increase. In 2001, groundnut/maize intercrop resulted in significantly higher maize grain yield (1.49 t ha-1) than the other treatments. Comparing between maize grain yields in 2001 and 2002, maize grain improved by 20.1% under sole maize, 95% under maize in sole groundnut, 92.8% under maize in soybean and 98.4% under maize in cowpea. This would confirm that the sole legume planting for two years restored fertility status of the soils and enhanced the soil organic carbon and total nitrogen, to have resulted in greater maize yield than under the sole maize despite the 120 kg N fertilizer applied to the sole maize

Ogunwole, J.O. 2004. Effects of fertilizer and time of ridge-tie on yield and fibre quality of late sown cotton in the dry Savanna Zone of Nigeria. Journal of Sustainable Agriculture, Vol. 24 (3):97-107

Field trials were conducted during the rainy seasons of 1999-2001 on the experimental farms of the Institute for Agricultural Research (IAR), Samaru to evaluate effects of fertilizer and time of ridge-tie on yield and fibre quality of late sown cotton. The treatments were a factorial combination of three fertilizer (N: P: K) levels (i.e. zero, 30:15:15 and 60:15:15) and, four times of ridge-tie (no-tie, 4,6, and 8 weeks after planting). Observation revealed about 80% yield increment when ridge were tied at 4 and 6 weeks after planting (WAP). Fertilizer rate of 30:15:15 optimum for late sown cotton in the area. Effective ridge-tie (6 WAP) reduced fibre length but produced the better fibre in terms of fineness. Fertilizer rates did not influence fibre quality except for fibre length, where increased fertilizer rate reduced fibre length

Ogunwole, J.O., J.J. Owonubi and A.L. Bello 2002. Solar radiation interception, dry matter production and yield of sorghum/maize mixtures at Samaru, northern Nigeria. Samaru Journal Agricultural Res. 18:25-32

Two varieties of sorghum, SAMSORG 14 and Farafara, were each intercropped with maize at two planting patterns at Samaru in 1996 and 1997 seasons. Result revealed a higher light interception of the intercrop over the sorghum sole crops, a higher efficiency of light conversion in the intercrop over the various sole crops, with row arrangement doing better than the stand arrangement. The row intercropping system favored maize performance in the two years under consideration. In addition, the intercrop displayed a higher space use efficiency over the various sole crops. This result further reaffirms the advantage of intercropping over the monocropping system in the dry Savanna.

Ogunwole, J.O., I.E. Esu, T. Kparmwang and V.O. Chude 2001. Effects of prolonged shaking periods and contents of iron oxides on dispersion of plinthitic soil in Nigeria. Commun. Soil Sci. Plant Anal., 32(13&14), 2293–2306

The dispersion of sesquioxide-rich or plinthitic soils is difficult and not completely achieved within routine dispersion period. Two prolonged shaking periods of 24 and 48 hours were tested to see which gives a more complete dispersion of two plinthtic soils-a drier Plinthustalf and a more humid Plinthustult. Iron oxides which are the main aggregating agents in plinthite were also determined and the iron ratios calculated to relate their contents to the rate of dispersion of the soils. Results showed that prolonged shaking for 24 hours gave greater dispersion which changed the textural classification of the soils from the routine time (5 minutes shaking) to finer textural classes. Shaking for 48 hours increased the clay content significantly (P = 0.001) over that of the 24 hours but textural classification did not change further. The soil clay was aggregated mainly into silt-size particles as the clay content increased at the expense of the silt fraction on prolonged dispersion period. Both the amorphous and crystalline inorganic iron (Fe) oxides were responsible for aggregation in the soils, and their effects were enhanced by desiccation. Dispersion was therefore more difficult in the drier Plinthustalf than in the more humid Plinthustult

Ogunwole, J.O., O.A. Babalola, E.Y. Oyinlola and B.A. Raji 2001. A pedological characterization of soils in the Samaru area of Nigeria. Samaru Journal of Agricultural Res. 17:71-77

Soils of the Samaru area of Nigeria were studied. The soils are deep with evidence of fauna pedoturbation, eluviations-illuviation and clay lessivation. The soils have epipedons and argillic diagnostic horizons. The soil texture ranged from sandy loam through clay with very high silt content (22 – 44%). Exchangeable bases were moderate to high. All the soils are low in organic matter content and deficient in total nitrogen. According to the USDA system of classification, the soils are classified as Typic Haplustalfs and Haptic Luvisols in the FAO/UNESCO Soil Legend

Ogunwole, J.O., B.A. Raji and E.O. Adewumi 2000. Effect of varying energy impacts on the physical properties of a Typic Haplustalf. Nigerian J. Soil Res. 1:4-7

Energy impact changes the physical properties of a soil. The response of a sandy loam soil was investigated under varying levels of energy impacts and moisture contents. Results showed that antecedent moisture content of the soil and the different energy levels have a pronounced effect on soil bulk density, surface soil penetration resistance and saturated hydraulic conductivity. Soil bulk density increased from 1.57 to 1.74 Mg m-3 as a result of energy impact and from 1.65 o 1.71 Mg m-3 as a result of antecedent moisture. The effect of energy impact was reduced at moisture content above 0.22 cm3 cm-3. The implications of these results on soil-plant relations were discussed. It was concluded that agricultural operations which could easily compact soil be performed at moisture content greater than 0.22 cm3 cm-3

Joshua O. Ogunwole, Luis C. Timm, Evelyn O. Obidike-Ugwu, Donald M. Gabriels, 2014. State-space estimation of soil organic carbon stock. International Agrophysics, 28, 185-194.

Understanding soil spatial variability and identifying soil parameters most determinant to soil organic carbon stock is pivotal to precision in ecological modelling, prediction, estimation and management of soil within a landscape. This study investigates and describes field soil variability and its structural pattern for agricultural management decisions. The main aim was to relate variation in soil organic carbon stock to soil properties and to estimate soil organic carbon stock from the soil properties. A transect sampling of 100 points at 3 m intervals was carried out. Soils were sampled and analyzed for soil organic carbon and other selected soil properties along with determination of dry aggregate and water-stable aggregate fractions. Principal component analysis, geostatistics, and state-space analysis were conducted on the analyzed soil properties. The first three principal components explained 53.2% of the total variation; Principal Component 1 was dominated by soil exchange complex and dry sieved macroaggregates clusters. Exponential semivariogram model described the structure of soil organic carbon stock with a strong dependence indicating that soil organic carbon values were correlated up to 10.8m.Neighbouring values of soil organic carbon stock, all waterstable aggregate fractions, and dithionite and pyrophosphate iron gave reliable estimate of soil organic carbon stock by state-space.

Ogunwole, J.O., E.O. Obidike, L.C. Timm, A.C. Odunze and D. Gabriels. Assessment of spatial distribution of selected soil properties using geo-spatial statistical tools. Communications in Soil Science and Plant Analysis (In Press).

In order to gain additional knowledge and better understand forest soil management at small scale, geostatistical analytical tools were employed to examine the spatial distribution in dry aggregate mean weight diameter (MWD) and other selected soil properties and, to assess the possible relationships between MWD and the rest soil properties. Selected properties of forest soils collected along a 300-m transact in the Nimbia Forest Reserve of Nigeria exhibited moderate to high variability in distribution with sodium ion displaying the highest variability (CV, 91.2%) and principal component analysis revealed the exchange complex cluster as influencing total variation of field soil properties. The autocorrelation function showed significant spatial correlation from 1 lag in soil organic carbon up to 17 lags (51 m) in soil moisture content (?). The spherical and Gaussian semivariogram models described spatial structure of most soil properties however, for clay, CEC and SOC; exponential model analyzed their spatial dependence.

Lawal, H.M., J.O.Ogunwole, E.O. Uyovbisere 2012. Reciprocal relationship between aggregate stability and organic carbon characteristics in a forested ecosystem of northern Nigeria. Tropical and Subtropical Agro-ecosystems, 15: 481- 488.

Soil organic matter associated with different size aggregates differ in structure and function; therefore, play different roles in soil organic carbon (SOC) turnover. This study assessed the relationship between aggregate stability and soil organic carbon fractions in a forested soil. Aggregate stability characterized by mean weight diameter (MWD) was correlated with the various pools of SOC in a regression model. Mean weight diameter presented a 46% influence on total organic carbon while, total organic carbon accounts for 21.8% of aggregate stability. The unprotected and physically protected soil organic carbon did not significantly dictate stability of these soils. However, chemically protected & biochemically protected SOC influenced significantly, aggregate stability of these forested soils

Halilu, A.D., S.M. Misari, C.A. Echekwe, O. Alabi, I.U. Abubakar, M.K. Saleh, A.O. Adeyanju and J. Ogunwole, 2011. Survey and collection of Jatropha curcas L. in the northwestern Savannas of Nigeria. Biomass and Bioenergy, 35: 4145-4148.

The Existence and Distribution of Jatropha curcas L. germplasms in the Northwest zone of Nigeria is hereby reported with coordinates and point mapping. Fifty seven (57) accessions were collected from the seven States of the zone which spans across the Sahel, Sudan and Guinea Savannas. The collection was made from 18th to 22nd of August 2009. A plantation was established from these collections and the seeds from 39 different provenances of the seven States were analyzed for their oil content. The mean oil content ranged from 20.29% to 61.83% (CV 29.11%). The 100-seed weight ranged from 28.558g to 80.046g. There was a positive correlation between 100 seed weight and oil content (r ¼ 0.235). The accessions from Kaduna State, spanning through the Sudan and Northern Guinea Savanna, had the highest mean oil content followed by those from Kano and Katsina States in the Sudan Savanna ecology. There were no significant differences ( p

Ogunwole J.O., E.N.O. Iwuafor, N.M. Eche, J. Diels 2010. Effect of organic and inorganic soil amendments on soil physical and chemical properties in a West African Savanna agroecosystem. Tropical and Subtropical Agro-ecosystems, 12: 247-255.

Long term agroecosystem productivity has stirred up the need to develop and implement nutrient management strategies that maintain and protect soil resources. In an attempt to address this, the current study involved the incorporation of residues of Centrosema pascorum, Lablab purpureus and Pakia biglobosa. In addition, an inorganic fertilizer amended soil and, a maize/lablab purpureus intercrop, along with the control (no amendment) was included. The treatments were replicated three times and the site had been under continuous cultivation for eight years in a Savanna Alfisol. Soil quality (physical and chemical) indicators were examined for treatments effects. Dry macroaggregate turnover increased by 7% under Centrosema pascorum amended soils. This same treatment had more water stable large microaggregates and a 40% increase in aggregated silt and clay content. Soil bulk density and saturated hydraulic conductivity reduced in nutrient management practices involving residue incorporation. However, soil organic carbon, total soil nitrogen, exchangeable Ca2+ and Mg2+ concentration were highest with soil receiving Centrosema pascorum. Crop residue management practices involving incorporation of Centrosema pascorum significantly improved soil physical and chemical properties of the study area

Oyinlola, E.Y., J.O. Ogunwole, I.Y. Amapu 2010. Response of sunflower (Helianthus annuus L.) to nitrogen application in a Savanna Alfisol. Helia 33 (Nr. 52): 115-126

Decline in crop yield has beed a major problem in Northern Guinea Savanna of Nigeria due to inherent low fertility status of the soils. Field experiments were conducted for two years (2003 & 2004) on an Alfisol of the Northern Guinea Savanna of Nigeria to determine the effect of N fertilizer on growth and yield parameters of sunflower. Six rates of nitrogen (0, 30, 60, 90, 120 & 150 kg N ha-1) were applied. Plant heights of 120 & 138 cm were obtained in 2003 and 2004 respectively, at 120 kg N ha-1. Application of N significantly increased seed and oil yields while excess N (150 kg N ha-1) reduced the contents of the two parameters. Optimum nitrogen requirement of sunflower obtained from this study is between 90 & 100 Kg N ha-1.

Lawal, H.M., J.O.Ogunwole, E.O. Uyovbisere 2009. Changes in soil aggregate stability and carbon sequestration mediated by land use practices in a degraded dry savanna Alfisol. Tropical and Subtropical Agro-ecosystems, 10: 423-429

Effects of land use practices on aggregate stability and fractions of soil organic carbon were investigated using physical fractionation procedure. Soils were sampled at three depths (0-5, 5-10 & 10-15 cm) under arable cropping, native vegetation and forest plantation. These soils were separated into aggregates to calculate mean weight diameter (MWD) and aggregate associated carbon. Results showed that MWD increased in soils under forest plantation by 61.4% relative to the soils under arable cropping practice. The macroaggregate fraction in the forested soils was 76.2% more than those soils under arable cropping. Chemically protected carbon was higher by 39% in soil under arable cropping compared to forested soil. Forest plantations therefore may have potential to increase the structural stability of soils and their resistance to soil erosion. Arable cropping seems to favour increasing carbon sequestration relative to native vegetation and Eucalyptus forested soils.

Ogunwole, J.O. 2008. Aggregate characteristics and organic carbon concentrations after 45 annual applications of manure and inorganic fertilizer. Biological Agriculture and Horticulture (Great Britain: AB Academic Press), 25(3): 223-233

Soil management practices that increase soil carbon sequestration can improve soil quality and reduce agricultural contribution to carbon dioxide emissions. The long term (45 years) effect of applications of manure (FYM) and inorganic (NPK) fertilizers on soil aggregate characteristics and soil organic carbon (SOC) concentration was studied in surface soils of a Typic Haplustalf, sandy loam. Soils from four treatments: inorganic fertilizer combined with farmyard manure (FYM +NPK), fertilizer only (NPK), farmyard manure only (FYM) and a control receiving neither NPK nor FYM were studied. Results indicate that long term application of manure with or without NPK improved aggregate stability by increasing mean weight diameter (MWD) of dry aggregate and fraction of dry aggregate > 2 mm. Higher values of MWD were also recorded in the water stable aggregate size distributions for soils amended with either FYM or NPK. Soils amended with FYM + NPK sequestered more SOC than all other treatments. There was a low but significant positive correlation between MWD of dry aggregates and SOC. Highest values of SOC were recorded in the > 2.0 mm dry aggregate is suggestive of the effectiveness of this aggregate size range to sequestered SOC in Savanna Alfisols. These results demonstrate that continuous application of soil amendments like FYM & NPK over a long term promotes soil aggregate stability and long term SOC sequestration. Hence, for sustainable production in Savanna Alfisols, there is need to design policies that will promote soil aggregate stability and long term carbon sequestration under continuous cultivation. Such policies must give attention to soil management practices that maintain higher level of SOC. Here, FYM with or without NPK was essential to increase stability of dry aggregates and SOC sequestration.

Ogunwole, J.O., D.R. Chaudhary, A. Ghosh, C.K. Daudu, J. Chikara and J.S. Patolia, 2008. Contribution of Jatropha curcas to soil quality improvement in a degraded Indian entisol. Acta Agriculturae Scandinavica Section B-Soil and Plant Science, 1-7

Soil quality improvement is critical to any rehabilitation programme in dry land degraded ecosystems. This study reports on the impact of cultivation of Jatropha curcas with or without soil amendments on the structural stability, and carbon and nitrogen content of a degraded Entisol under rehabilitation in western India. Cultivation of Jatropha curcas resulted in 11% average increase in mean weight diameter of the soil and 2% increase in soil macro-aggregate turnover. Cultivation of Jatropha curcas with nitrogen and phosphorus- or without any-amendment improved macro-aggregate stability relative to nearby native vegetation. Regression analysis showed a significant correlation between organic carbon and mean weight diameter. The cultivation of Jatropha curcas appeared to have also contributed to the quality of these soils as it maintained organic carbon and nitrogen stock and displayed a potential to increase carbon sequestration rate. Soil structure recovery under cultivation of Jatropha curcas implies a sustainable improvement in the surface integrity of these soils, which will ensure more water infiltration rather than runoff and erosion

Horn, R., C. Johnson, H. Semmel, R. Schafer and M. Lebert (1992). STRESS MEASUREMENTS IN UNDISTURBED UNSATURATED SOILS WITH A STRESS STATE TRANSDUCER (SST) - THEORY AND 1ST RESULTS. Zeitschrift Fur Pflanzenernahrung Und Bodenkunde 155(4): 269-274.

A method to quantify the spatial stress distribution will be introduced and first results will be discussed. This method allows the detailed analysis of principal and shear stresses as well as the determination of the direction angle of principal stresses and the octahedral shear stress angle. The described Stress State Transducer (SST) is composed of six single strain gage sensors that enable the accurate and recording of stresses in six directions in a wide load range. Their data form the base for calculation of spatial stress distribution. Some first results show that in a luvisol derived from loess wheeling at a wheel load of 4.0 Mg induces high shear stresses in a depth of 30 cm. This probably causes plastic soil deformation.

Horn, R., T. Baumgartl, S. Kuhner, M. Lebert and R. Kayser (1991). THE EFFECT OF SOIL AGGREGATION ON STRESS-DISTRIBUTION IN STRUCTURED SOILS. Zeitschrift Fur Pflanzenernahrung Und Bodenkunde 154(1): 21-26.

The mechanical compressibility of arable soils can be described by preconsolidation load value and by the shear resistance parameters of the bulk soil and single aggregates. In order to quantify the effective stress equation must be also known the hydraulic properties of the soil in dependence of the intensity, kind, and number of loading events. The soil reacts as a rigid body at very fast wheeling speed inclusive a very pronounced stress attenuation in the top soil while stresses will be distributed in the soil threedimensionally to deeper depths at slower speed. These variations can be explained by the mechanical as well as by the hydraulic parameters of the bulk soil and single aggregates. Thus, the pore water pressure value of the bulk soil as a parameter of the effective stress equation further depends on the hydraulic properties of the inter- and intraaggregate pore system and continuity. As can be derived from the results the pore water pressure values are identical irrespective of the predessication for clayey polyhedres at high load while in coarse textured prisms the pore water pressure value depends on load and predryness. The consequences for soil strength under dynamic loading are shortly discussed.

Lebert, M. and R. Horn (1991). A METHOD TO PREDICT THE MECHANICAL STRENGTH OF AGRICULTURAL SOILS. Soil & Tillage Research 19(2-3): 275-286.

During a 3-year period the physical and mechanical properties of 37 typical, differently textured and structured agricultural soils in Bavaria were determined in order to predict their mechanical compressibility and trafficability. The soil physical properties (bulk density, pore size distribution, saturated hydraulic conductivity, air permeability and penetration resistance) and the soil mechanical properties (pre-consolidation load and the shear strength parameters angle of internal friction and cohesion), were determined on undisturbed, differently pre-dried soil samples (60 and 300 hPa water tension). In order to quantify the changes in soil physical properties affected by loading, all soil physical parameters were measured before and after loading by the confined compression test (load range 10-800 kPa). It was found that in homogeneous, non-structured soils, such as sands and silts with low clay content ( 15% w/w), stability increased with increasing degree of aggregation (coherent

Lebert, M. (2010). A method to assess the vulnerability of agricultural subsoils to compaction. Proceedings of the 19th World Congress of Soil Science: Soil solutions for a changing world, Brisbane, Australia, 1-6 August 2010. Symposium 3.1.1 Further development of soil evaluation methods: 5-8.

The method proposed consists of three steps to derive the vulnerability of subsoils to compaction. In the first step, the mechanical susceptibility to compaction is determined by the pre-compression stress with pedotransfer functions. In the second step, soil structural quality of subsoils is determined by the evaluation of soil physical properties as air capacity, saturated water conductivity and packing density. In the third step, vulnerability to compaction is derived by combining the mechanical susceptibility to compaction with the soil structural quality. The method is based on the evaluation of actually analysed soil physical data from 1300 representative agricultural subsoils in Germany, offered by the soil surveys of the federal states. The results are shown in maps of 1:1.000.000 scale. At the water content of 100% field capacity, about 60% of the German subsoils are high vulnerable to compaction, including marshlands, clayey river sediments, glacial loams, loessian soils, periglacial clays and loamy and clayey soils derived from weather beaten rocks and sediments. Pure and loamy sands have low vulnerability. At the water content of 80% field capacity, low, medium and high vulnerability are distributed about one third each over the arable area in Germany.

Rucknagel, J. Brandhuber, R. Hofmann, B. Lebert, M. Marschall, K. Paul, R. Stock, O. Christen, O. (2010). Variance of mechanical precompression stress in graphic estimations using the Casagrande method and derived mathematical models. Soil & Tillage Research. 106, 165-170.

Mechanical precompression stress is a yardstick for the strength and compressibility of soils. The default method for the estimation of precompression stress is the graphic method according to Casagrande. It involves a Subjective perception by the engineer who not only determines the point of the highest curvature visually, but decides also which points are to be used for generating the virgin compression line. In order to avoid such subjective approaches, mathematical models for the determination of precompression stress have been developed emanating from the Casagrande method. These models estimate the smallest radius of the curvature based on the minimum of the second numerical derivative. The paper has the aim to quantify the variance of subjectivity implied by the person executing the graphic method, the variance of different model approaches and the accuracy of the latter in handling the graphic values. Additionally we wanted to investigate the effect of different parameters on the ordinate of the diagram and the effect of the first load step on the precompression stress. To understand these relationships, stress/bulk density functions and stress/void ratio functions measured on 13 sites were analysed by five experienced but independent engineers and by use of three mathematical models. The mean errors of precompression stress estimations by the different testers were 0.01-0.12 and by the models 0.10-0.87 on a logarithmic scale. Expressed in kPa, increasing mean errors were observed with rising precompression stress, due to delogarithmization. For the graphical determination, they reached approx. 10-20 kPa at precompression stress levels of 60-150 kPa in typical subsoils: this means 15% on average. The handling of graphically obtained values by help of mathematical models disclosed considerable deviations between them. In the logarithmic variant, the mean absolute errors varied from 0.09 (9 kPa) to 0.40 (30 kPa) and the determination coefficients from 0.71 to 0.96. Another influence on the level of precompression stress has been observed when different variables were plotted on the ordinate of the graph. The graphically obtained values of precompression stress and those shown in the dry bulk density graph exceed the values calculated on the basis of the void ratio by the factor 1.2-1.5. Furthermore, it can be stated that in soil-compression tests with an initial load of 25 kPa higher precompression stress values were obtained than with lower initial loads (5 kPa), if the precompression values were low.

Lebert, M., J. Brunotte, C. Sommer and H. Boken (2006). Protecting soil structure against compaction - proposed solutions to safeguard agricultural soils. Journal of Plant Nutrition and Soil Science-Zeitschrift Fur Pflanzenernahrung Und Bodenkunde 169(5): 633-641.

To safeguard the ecological soil functions and the functions linked to human activities, measures against harmful changes to the soil are required, in line with the precautionary principle. The German Federal Soil Protection Act sets obligations for precaution in agricultural land use and, if harmful changes to the soil are foreseeable, measures for averting a danger. The results of a research project of the Federal Environmental Agency show that it is possible to describe an impairment of the soil structure, using methods of soil analysis. But this as a sole information would not quality for the identification of harmful changes to the soil in the context of the Soil Protection Act, which requires an assessment of the severity of disruption of soil functions and the respective subject of protection. This would make additional soil investigations on site mandatory. Approaches in agricultural engineering and soil physics have introduced procedures to preserve the soil structure, in accordance with the precautionary principle. But these procedures have different goals and different ranges of application and hence offer partial solutions to safeguard against soil compaction. The assessment model of "trafficability by measuring the rut depth" provides information about the compaction status of the soil under applied conditions for farming gear, without providing detailed information about affected soil layers. The soil-physical model of classifying soils into "risk classes for harmful soil compaction" focuses on the relationship between topsoil compaction and crop yields. The soil-physical models "precompression stress" and "loading ratio" provide information for the assessment of subsoil compaction and a prognosis of a possible impairment of the soil structure at the water content of field capacity. It is necessary to validate the individual models with additional regional data about soil structure before a final assessment of the prognoses is made.

Springob, G. and M. Lebert (1994). CRITICAL LIMITS OF SOIL TESTS FOR K AS DERIVED FROM RELATIONSHIPS BETWEEN TOPSOIL K AND TISSUE WATER K OF PLANTS. Agribiological Research-Zeitschrift Fur Agrarbiologie Agrikulturchemie Okologie 47(3-4): 303-311.

A statistical procedure is proposed to simultaneously determine minimum critical soil test values for K and critical plant K concentrations from relationship between topsoil K and the K concentration in the tissue water of winter wheat plants. Soil K was extracted from both, fieldmoist and airdried samples, using the conventional NH(4)acetate (exchangeable K), CAL and CaCl2 procedures. The closest soil-plant correlation (r(2)=0.602) was found for the exchangeable K of moist soils, the weakest for the K-CaCl2 of dried samples (r(2)=0.547) and KCAL was inbetween (r(2)=0.583). In all cases saturation curves were obtained approaching constant levels of 207 mmol K l(-1) tissue water (plant critical value) when asymptotic models were fitted to the data. The amount of soil K related to the onset of the plateau is defined as the soil K critical level. It is derived by fitting several asymptotic functions to the data among which the RICHARDS function (RICHARDS, 1959) performed best. Tentative critical limits for the routine NH4 extraction are 1.25 mg K g(-1) clay for moist and 1.12 mg K-1 clay for dried soils, respectively, and for the CAL procedure 0.85 mg K g(-1) clay for moist and 0.93 mg K g(-1) clay for dried samples, respectively. For K-CaCl2, moist and dried soil samples yielded similar critical values of about 80 mg K g(-1) soil. Critical values like these appear to be useful limits when reductions of soil K levels in previousely overfertilized soils are in progress.