Rainfall characteristics were evaluated in Makurdi in the Guinea Savanna agroclimatic belt of Nigeria. Pluviograhic rainfall data were collected for the period 1985 to 1987. The mean Annual rainfall was 1140mm.The highest rainfall amount per storm event was 71.7mm while the highest six- minute rainfall intensity was 240mmh-1. The mean monthly Kinetic energy (E) using the Wischmeier and Smith (1978) equation ranged from 2.0 to 84.1MJha-1 whereas the value ranged from 2.5 to 128.0MJha-1 using Kowal and Kassam (1976) equation (designated Ek).Conventional rainfall erosivity used for evaluation were the EI30, K.E > 25 and AIm. The ranges of monthly erosivity based on these indices were 24 to 406 MJ.mmha-1h-1, 0.7 to 9.0MJha-1 and 270 to 4280 mm2h-1 respectively. Following Obi and Salako (1995) additional indices, namely, E(A), EkI30, EkIm ,E(A)I30 and EkAIm were evaluated. Mean monthly erosivity values ranges based on these indices were 18 to 471 MJ.mmha-1h-1, 31 to 595 MJ.mmha-1h-1, 76 to 1594 MJ.mmha-1h-1, 218 to 26992 MJ.mmha-1h-1 and 527 to 67293 MJ.mmha-1h-1 respectively. The findings enable better understanding of the rainfall effects on soil erosion in the region. The generally high erosivity values are pointers to the compelling need for soil protective covers in particular and the integration of other serious conservation measures as key strategies for sustainable production in the agro-ecological zone.Keywords: Rainfall, Eosivity, USLE

Soil total porosity is, rather than measured by water desorption method, more often estimated from bulk density (BD) and assumed particle density. Measured and estimated total porosities of even kaolinitic tropical soils (which have low tendency to expand upon wetting) usually differ by an extent that depends on soil structural stability, but such differences are scarcely documented. Seventy samples of coarse-textured soils under different fallow- and cultivation-management systems in the southeastern region of Nigeria were analyzed for texture, mean-weight diameter (MWD) of aggregates, BD and organic matter (OM) concentration. Soil total porosities measured by water desorption method were compared with those estimated from BDs (with particle density fixed at 2.70 g cm−3), after grouping the soils by structural stability, assessed by OM/(silt + clay) for 50 of the samples from fallowed plots (BD > 1.48 g cm−3) and MWD for the rest from cultivated plots (BD < 1.48 g cm−3). The fallowed plots showed a wider stability range than the cultivated plots. Irrespective of land use, structural stability tended to increase with decreasing soil BD. Measured total porosities were consistently higher than their estimated counterparts, with the differences closing up with increasing soil structural stability up till a mean BD of 1.41 ± 0.05 g cm−3 (corresponding to MWD of 2.66 ± 0.12 mm), beyond which the trend reversed. These results suggest that, as the soil structural stability increases, soil particle density decreases while entrapped air and transitory drainage of saturated samples at weighing increase. Estimating total porosity with a fixed particle density of 2.70 g cm−3 appears suitable only in highly stable soils, with BD of ≤1.40 ± 0.08 g cm−3 and/or MWD of ≥2.92 ± 0.05 mm [corresponding to OM/(silt + clay) of ≥16.38 ± 0.28 %].

Lowland sawah farmers often puddle to improve soil hydrophysical conditions for rice, but the puddling intensity beyond which no extra yield increases occur is unknown. Agronomic effects of six mechanical puddling intensities were assessed in three Nigerian inland-valley bottoms. All puddled plots, irrespective of intensity, produced similar effects at all three locations. At 10 days after transplanting, soil bulk density of all puddled plots represented mean decreases relative to control plots of about 22.4, 15.8, and 31.7% at Akaeze, Adani, and Ejeti, respectively. Soil bulk density and moisture content upon saturation were similar during 40-120 days after transplanting. All puddled plots consistently showed taller plants and greater tillering than control plots only at Ejeti. Grain yields were similar among treatments in Akaeze and Adani (mean, 3.71 and 6.42 Mg ha(-1), respectively), but one-pass puddling yielded numerically highest in both locations. At Ejeti, grain yields followed the trend for plant growth, with mean values of 4.36 and 1.81 Mg ha(-1) for puddled and control plots, respectively. One-pass puddling may be sufficient for sawah rice grown late particularly in less humid environments.

The spatial variability of some physicochemical properties of topsoils/subsoils under secondary forest, grassland fallow, and bare-soil fallow of three locations was evaluated. The data were analyzed and described using classical statistical parameters. Based on the coefficient of variation, bulk density, total porosity, 60-cm-tension moisture content, and soil pH were of low variability. Coarse and fine sand were of moderate variability. Highly variable soil properties included silt, clay, macroporosity, saturated hydraulic conductivity, organic matter concentration, and cation exchange capacity. Overall, soil pH and silt varied the least and the most, respectively. Relative weighting showed that location dominantly influenced the soil variability, except for soil porosity and organic matter concentration influenced mostly by land use. Most of the soil data were normally distributed; others were positively skewed and/or kurtotic. The minimum number of samples (at 25 samples ha(-1)) required to estimate mean values of soil properties was highly soil property-specific, ranging from 1 (topsoil pH-H2O) to 246 (topsoil silt). Cation exchange capacity of subsoils related fairly strongly with cation exchange capacity of topsoils (R-2 = 0.63). Spatial variability data can be used to extrapolate dynamic soil properties across a derived-savanna landscape.

Studies were conducted in the runoff plots at the University of Nigeria Nsukka Teaching and Resesarch Farm in 2010 and 2011 to monitor the changes in structural stability and saturated hydraulic conductivity (Ksat) of Nkpologu sandy loam soil under different cover management practices. The management practices were bare fallow (BF), grass fallow (GF), legume (CE), groundnut (GN), sorghum (SM), and cassava (CA) cultivation. Three samplings were carried out at the study site following the characterization of the soil at five- month interval marking the end of first cropping season, and the start and end of the second cropping season respectively. There was no change in soil texture due to treatments. The aggregate stability (AS), mean weight diameter (MWD), water dispersible silt (WDSi), aggregate size distributions (> 2 mm, 1-0.5 mm and < 0.25 mm) and Ksat showed significant (P =0.05) changes with time. Ksat varied (CV = 52%) significantly (P = 0.05) with a standard deviation (SD) value of 7.8. The highest values for Ksat, AS and MWD were obtained in the first sampling period whereas the lowest values were obtained in the last sampling period. There were significant effect (P =0.05) of cover management practices on AS, MWD and Ksat. The highest values for AS, MWD and aggregate size fraction > 2 mm were obtained under GF whereas the highest Ksat was obtained under GN. The lowest values for these parameters throughout the sampling periods were obtained under BF. The preponderance of aggregates < 0.5 mm under BF showed that raindrop impact and other agents broke down macroaggregates into microaggregates. The cover treatments generally increased organic matter (O.M.) content compared with the BF. The O.M. had significant correlation with two aggregate size ranges; 1-0.5mm (r = - 0.276* at P=0.05) and 0.5-0.25mm (r = - 0.245*at P =0.05). The study has shown that cover management practices affected the structural properties of the tropical sandy loam soil differently over time.Keywords: Aggregate stability, MWD, aggregate size distribution, macroaggregates, microaggregates, saturated hydraulic conductivity, Cover management.

The roles of fine-earth materials in the cation exchange capacity (CEC) of especially homogenous units of the kaolinitic and oxyhydroxidic tropical soils are still unclear. The CEC (pH 7) of some coarse-textured soils from southeastern Nigeria were related to their total sand, coarse sand (CS), fine sand (FS), silt, clay, and organic-matter (OM) contents before and after partitioning the dataset into topsoils and subsoils and into very-low-, low-, and moderate-/high-stability soils. The soil-layer categories showed similar CEC values; the stability categories did not. The CEC increased with decreasing CS but with increasing FS. Silt correlated negatively with the CEC, except in the moderate- to high-stability soils. Conversely, clay and OM generally impacted positively on the CEC. The best-fitting linear CEC function (R-2, 68%) was attained with FS, clay, and OM with relative contributions of 26, 38, and 36%, respectively. However, more reliable models were attained after partitioning by soil layer (R-2, 71-76%) and by soil stability (R-2, 81-86%). Notably FS's contribution to CEC increased while clay's decreased with increasing soil stability. Clay alone satisfactorily modeled the CEC for the very-low-stability soils, whereas silt contributed more than OM to the CEC of the moderate- to high-stability soils. These results provide new evidence about the cation exchange behavior of FS, silt, and clay in structurally contrasting tropical soils.

The effect of soil structure on hydraulic pedotransfer functions (PTFs) in tropical soils with similar mineralogy and texture has not been well documented. Structurally contrasting soils from representative locations in southeastern Nigeria were analyzed for moisture retention at 0, 6, 10, 33, 100, 300 and 1500 kPa among other properties. They were grouped by depth (topsoils or subsoils) and also by their structural degradation status into low‐ and high‐stability soils, corresponding to organic matter (OM):[silt + clay] of <7.5 and >7.5%, respectively. Soil depth and structural stability influenced the soil moisture characteristic curves. The data were fitted to three tropical point PTFs, but none of them proved appropriate for predicting moisture retention in the soils. We therefore derived new ones using multiple linear stepwise regressions before and after the dataset grouping and compared their performances by means of cross‐validation. Moisture retention in the soils (sand content, 73.2–93.8%) could not be calibrated from texture and OM concentration alone, until when bulk density, total porosity and microporosity were included among the regressors. Microporosity's role was particularly outstanding at all matric potentials but the 1500 kPa. The ensuing PTFs represent a good fit for the soil moisture retention data. The two grouping strategies resulted in lower SE of the estimates in some cases, but this did not enhance the performances of the concerned PTFs. At the 1500 kPa, however, the PTF incorporating all datasets performed better than separate PTFs for topsoils/subsoils but worse than the one for high‐stability soils. Information on soil structure can therefore benefit PTF derivation for kaolinite‐dominated, coarse‐textured tropical soils at all the matric potentials considered. Copyright © 2012 John Wiley & Sons, Ltd.

Quantitative data on carbon stock (C stock) in and beyond the topsoil (0–30 cm) under natural terrestrial ecosystems in West African savanna could provide information about their relative potential, and management options, for C sequestration, but these data are still scanty in the region. In selected locations (Nsukka, Obimo, and Ibagwa-aka) in the derived savanna zone of south-eastern Nigeria, secondary forest (SFT), grassland fallow (GLF), and bare footpath (BFP) were sampled from the topsoils (0–30 cm) and subsoils (30–60 cm) in triplicate. The soils are generally sandy, with low (1.4–13.8%) mean silt content. Mean bulk density ranged from 1.30 to 1.83 Mg/m3. The soils were acidic (pHwater 4.0–4.8) and low in organic C (0.10–1.14%). There was a consistent trend in C stock (SFT > GLF > BFP) in the topsoil, whereas only higher values in SFT than BFP were consistent in the subsoil. In both soil layers, the scale of the differences among the land-cover types was location-specific. Values of C stock were higher in the topsoil than subsoil, except for GLF and BFP at Obimo due to recent bush burning. Irrespective of location, the mean topsoil–subsoil values under SFT, GLF, and BFP were 45.7–30.6, 27.7–25.8, and 19.0–18.8 Mg/ha, respectively. Soil structural stability, indexed as the ratio of organic matter to silt + clay, explained roughly 61 and 89% of the variability in C stock of topsoils and subsoils, respectively. These results should benefit the planning of C sequestration projects in savanna agroecosystems of West Africa.

SUMMARYOver a decade after the forest-savanna transition zone of Nigeria was deemed suitable for production of sorghum (Sorghum bicolor), no research has been undertaken on the crop's tillage requirements in the southeastern part of the zone. This study evaluated the effects of tillage-mulch practices on soil moisture, water use (WU), grain yield and water use efficiency (WUE) of the crop in a Typic Paleustult (sandy loam) at Nsukka during 2006 and 2007 growing seasons. In a split-plot design, no-till (NT) and conventional tillage (CT) treatments were left bare (B) or covered with mulch (M) at 5 Mg ha−1. The ensuing treatments (NTB, NTM, CTB, and CTM) represented four tillage methods, which were replicated four times in a randomized complete block. In the monitored root zone, NTB and CTM significantly (p ≤ 0.05) enhanced the soil moisture status over NTM and CTB, but the main effects of the tillage and the mulch factors were not significant. The crop WU was uninfluenced by the treatments throughout the study. Although the grain yield showed higher values with NT than with CT, the differences were significant (p ≤ 0.05) only in 2007 that was marked with erratic rainfall and relatively low mean yield. Mulch significantly (p ≤ 0.05) enhanced the grain yield in 2006, with greater effect in CT than NT. On average, the mulch plots out-yielded their bare counterparts by about 26%. The tillage × mulch interaction was significant (p ≤ 0.01), and showed higher grain yields in NTB, NTM and CTM than in CTB. In the year-weighted average, yield increments in NTB, NTM and CTM over CTB were 53, 53 and 67% respectively, a pointer to the relevance of mulch with the CT but not the NT. Relative WU showed that the crop's water demand was met under all treatments. Hence, the yield reduction in the CTB was not due to water shortage. The WUE varied among the treatments in the same pattern as grain yield. In summary, NTB and CTM proved superior to NTM only in soil moisture status but to CTB in all measured parameters. From a socio-economic viewpoint, however, NTB would be preferable to CTM for growing sorghum in this area.

Evaluation of the impact of tillage-mulch practices under different cropping systems on soil physical properties is needed in southeastern Nigeria to identify those combinations with the potential of alleviating the physical constraints of the Ultisols predominant in the area. An investigation was carried out on a sandy loam soil at Nsukka to determine the effects of no-till (NT) and conventional tillage (CT) each with bare fallow (B) and mulch cover (M) on soil physical properties under three cropping systems [sole sorghum (Sorghum bicolor L. Moench), sole soybean (Glycine max L. Merrill), and sorghum-soybean intercrop]. The layout was a split-plot in randomized complete block design, with the tillage systems as the main plots and the mulch practices as the sub-plots. The treatments [no-till and bare (NTB), no-till with mulch (NTM), conventional tillage and bare (CTB) and conventional tillage with mulch (CTM)] were replicated four times. The selected key parameters evaluated after two years were density of earthworm casts, soil organic matter (SOM), bulk density (BD), total porosity (TP), pore size distribution (PSD), mean weight diameter (MWD), and saturated hydraulic conductivity (Ksat). Earthworm activity was significantly (P ≤ 0.001) higher with NT under the intercrop system. Values were generally very low for SOM (1.06-1.48%), moderate for BD (1.34-1.51 Mg m−3) and TP (46-52%), and low to moderate for MWD (1.1-2.9mm). The Ksat was within the slow to rapid range (8.1-57.0cm h−1). Neither the tillage nor the mulch factors influenced SOM, BD, PSD, and MWD in the cropping systems. The TP was significantly (P ≤ 0.05) higher in the CT compared to the NT under the sole sorghum, where interaction showed higher value in the CTM compared to the rest. There was significant (P ≤ 0.05) enhancement of Ksat in the CT under the sole sorghum and the intercrop systems; whereas the value was significantly (P ≤ 0.01) higher in the bare fallow under the sole soybean. The cropping systems had more pronounced effect on the physical properties than the tillage-mulch management practices. All the measured parameters indicated significant (P ≤ 0.05) improvements under the sole soybean, except BD and MWD which were significantly (P ≤ 0.05) improved under the intercrop. Intercropping cereals and legumes on NT may be ideal for alleviating the soil's structural constraints.

A study quantifying the productivity of selected soils in Nsukka and Abakaliki areas of Southeastern Nigeria was carried out for two cropping seasons using modified productivity index model. The study involved two modifications of Pierce et al. (1983) productivity index model. Maize was used as test crop. The first involved the exclusion of sufficiencies for aeration and electrical conductivity (PIM1). The second entailed the inclusion of sufficiencies for organic carbon, available phosphorus and exchangeable aluminium with simultaneous exclusion of sufficiencies for aeration and electrical conductivity (P1M2). Results from the experiment showed a highly significant relationship (r 2 = 0.92 at P < 0.01) between P1M2 and maize grain yield. However, there was a poor relationship (r 2 = 0.41 at P<0.05) between P1M1 and grain yield. Similarly, the inclusion of sufficiencies for organic carbon and available phosphorus increased the validity of P1M2.

Evaluation of the productivity of degraded Ultisol in Nsukka, South-Eastern Nigeria using Desurfacing Technique (DT) was carried out in 2002 and 2003 planting seasons using maize (Zea mays, variety; Oba Super II) as test crop. Desurfacing soil depths were 3 cm, 6 cm and 0 cm as control, while some soil characteristics, such as texture, bulk density, were used as measures of assessment of productivity. There were correlations between desurfacing depths and Leaf Area Index (LAI), plant height and seed yield in testing the predictive efficiencies of desurfacing technique (DT) in evaluating soil productivity. There were very significant correlations at P = 0.01, (r = 0.94, 0.96 and 0.94) between desurfacing depths and leaf area index (LAI), plant height and seed yield and P = 0.01 (r = 0.95, 0.94, and 0.94) between soil removal, and LAI, plant height and seed yield in poultry and meteorological sites respectively during the study periods. This shows that DT could be used in predicting the productive potential of degraded land on which management strategies for rehabilitating such degraded land can be used. Keywords: Degradation, Soil Productivity, Predictive Model, Soil Properties, Soil Erosion-Productivity Relationship, Sustainable Agriculture, Productive Index. International Journal of Agriculture and Development Vol. 9 2007: pp. 123-127

The effects of soil desurfacing on maize (Zen mays L) seed yield, plant height, leaf area index (LAI) were investigated in two locations (location I and location II) in South Eastern Nigeria. The soil loss depths were 0 cm (control), 3 cm and 6. cm. There were very significant correlations at P = 0.01 (r = 0.94, 0.96 and 0.94) between soil loss depths and leaf area index, (LAI), plant height and seed yield and P = 0.01 (r = 0.95, 0.94 and 0.94) between soil removal and LAI, plant height and seed yield in location I and location 11, respectively, during the study periods. These significant reductions in these crop parameters due to Surface sod loss were because of the reductions of the organic matter (2% and 18%) contents due to soil removal which affected these yield parameters. In comparison with 0 cm (control) at poultry site, yield reductions following 3 cm and 6 cm soil removal were 23%, and 55%, respectively. Corresponding yield reductions in locations 11 were 50% and 95%. There were also 6% and 29% reductions in plant height following 3 cm and 6 cm Surface soil loss, respectively, while at the location 11 there were 20%, and 85% reductions in plant heights due to 3 cm and 6 cm top soil removal. Leaf area index (LAI) was also reduced, for there were 43% and 62% reductions at location I and 42% and 94% in location 11 due to 3 cm and 6 cm top soil removal depths, respectively. The generally poor maize yield on eroded soils, even with NPK chemical fertilizer applications alone may not restore productivity on eroded areas.

The widespread incidence of soil erosion in the tropics has been identified, though few studies have dealt with specific problems of decline in crop productivity associated with soil loss. An understanding of the influence of surface soil loss on crop yield is necessary in order to find out their effects on performance of crops. Effects of surface soil loss on maize ( Zea mays L) seed yield, plant height and leaf area index (LAI) were investigated in poultry and meteorological locations in South Eastern Nigeria. The soil loss depths were 0 cm (control), 3 cm and 6 cm. There were very significant correlations at P = 0.01 (r = 0.94, 0.96 and 0.94) between soil loss depths and leaf area index, (LAI), plant height and seed yield and also at P = 0.01 (r = 0.95, 0.94 and 0.94) between soil removal and LAI, plant height and seed yield in poultry and meteorological sites respectively during the study periods. The significant reductions in these crop parameters due to surface soil loss were because of the reductions of the organic matter (2% and 18%) contents due to soil removal which affected the yield parameters. In comparison with 0 cm (control) at poultry site, yield reductions following 3 cm and 6 cm soil removal were 23% and 55% respectively. Corresponding yield reductions in meteorological locations were 50% and 95%. There were also 6% and 29% reductions in plant height following 3 cm and 6 cm surface soil loss, respectively, while at the meteorological location there were 20% and 85% reductions in plant heights due to 3 cm and 6 cm top soil removal. Leaf area index was also reduced, for there were 43% and 62% reductions at poultry locations and 42% and 94% in meteorological location due to 3 cm and 6 cm top soil removal respectively. The generally poor maize yield on eroded soils, even with NPK fertilizer amendments alone means that this treatment may not restore productivity on eroded areas. Keywords : surface soil loss, erosion effects, leaf area index, seed yield, plant height, productivity reduction, south eastern soils Nigeria Journal of Soil Research Vol. 6 2005: 1-8

Frequent occurrences of soil compaction damage resulting from high raindrop impact energy, and from human and animal trafficking during field operations pose a problem to farmers around the tropics. We studied the effect of some crop and soil management practices (manure, mulch, NPK applications, tillage and crop type) on some soil compactibility indices (dry bulk density, cone index, total soil porosity, gravimetric soil water content) in a Typic Paleustult in southeastern Nigeria. The study was carried out for three consecutive planting seasons using two tillage systems and four other soil management practices (poultry droppings + NPK, mulch + NPK, NPK alone and no amendment). These were laid out as split-plot in a RCB design replicated three times and using maize (Zea mays L.) and groundnut (Arachis hypogea) as test crops. Results indicate that the different soil management techniques adopted influenced dry bulk density, penetration resistance, total soil porosity and gravimetric soil water content at 44 and 66 days after planting (DAP) whereas only gravimetric soil water content was affected at 90 DAP. The dry bulk density of tilled maize and groundnut plots increased significantly (P<0.05) by between 2 and 14% relative to no-till plots at 44 and 66 DAP. In both maize and groundnut plots, dry bulk density decreased significantly (P<0.05) in plots amended with poultry droppings +NPK relative to the control plots by 3–10% at 44 and 66 DAP. Tilled maize and groundnut plots had 37–45% lower (P< 0.05) penetration resistance than their corresponding no-till plots at both 44 and 66 DAP. Penetration resistance measurements were lower by 16.5–25% in plots amended with poultry droppings + NPK relative to unamended plots at 44 and 66 DAP. Cumulative (1996, 1997, 1998) data indicate that gravimetric soil water content in maize and groundnut plots generally increased significantly (P<0.05) in no-till plots relative to tilled plots by 18–27% at both 44 and 66 DAP. Plots amended with poultry droppings + NPK had between 24 and 111% increase (P<0.05) in soil gravimetric soil water content at both 44 and 66 DAP. Results are indicative that all soil compactibility indices measured were not affected at 90 DAP except for soil gravimetric soil water content in 1996 and 1998. Results from this work demonstrate that some crop and soil management practices could be used to reduce soil compactibility problems thus increasing productivity of such soils.