Influence of Method of Residue Application and Moisture Content on Water Soluble Nitrogen in a RhodicKandiustalf Amended with Different Fallow Plant Materials

Use of plant residues as nutrient sources presents a viable option to resource poor farmers who sparsely use mineral fertilizer in crop production. A study was conducted to gain an insight into how different application methods of residues from different fallow management systems under two moisture regimes would affect soluble N release in a Rhodic Kandiustalf. Three residue types viz, elephant grass from a natural fallow (T1) and another as a fallow following a previously fertilized maize (T2) and a fallow legume (T3) were surface applied and incorporated in a Rhodic Kandiustalf at both field capacity (FC) and 60% field capacity over a sixteen-week period. Incorporation of mucuna residues and elephant grass from previously fertilized maize fallow released similar soluble N levels which were higher than levels from the natural elephant grass amendments. At 60% FC, both mucuna and elephant grass from the fertilized maize fields that were surface applied had slower N releases than the grass from the natural fallow, suggesting the elephant grass from the natural fallow field could be used as an N source amidst light watering to avoid leaching in the dry season

Scaling the saturated hydraulic conductivity of an Alfisol

Alfisols exhibit a high degree of spatial variability in their physical properties. As a result, it is difficult to use information on physical parameters measured at one location to model larger-scale hydrologic processes. In this study, the saturated hydraulic conductivity, Ks, of an Alfisol was determined on 109 undisturbed monoliths using the falling-head permeameter method. The model developed by Arya & Paris (Soil Science Society of America Journal 45, 1023-1030, 1981) was used to calculate the pore volume from sand and clay fractions. Scaling factors were calculated from the measured Ks, sand pore-volume, clay pore-volume, clay content and effective porosity, using the similar media concept. Prediction of Ks of gravelly Alfisol using clay pore-volume is confounded by high gravel content which, when discounted, improves the prediction remarkably. The scaled mean saturated hydraulic conductivity K* for all horizons of the alfisol was approximately 1.0 × 10-5 m s-

Spatial variability in penetration resistance of a hardsetting tropical alfisol

Geostatistical techniques were used to analyse the spatial variation of penetration resistance on an experimental plot intended for root studies. Penetration resistance was measured at two soil water conditions. Penetration resistance exhibited spatial structure but the models describing the semivariograms were different for the two soil water conditions. An isotropic linear model provided the best fit for penetration resistance in the dry soil while an isotropic spherical model was used for penetration in the wet soil. A complementary study of the spatial structure of water content also showed a similar trend. Cross-semivariograms were constructed to determine the spatial relationship between penetration resistance and water content. Penetration resistance in the dry soil was negatively correlated with water content. The nugget variances as the percentage of the sill in the wet soil data set suggest that the topsoil was slightly more variable than the subsoil. The spatial scale of variation in penetration resistance of the wet soil was 33 m at 7.5 cm depth and 20–27 m at 15–30 cm depth. Punctual kriging was used to estimate the penetration resistance and water content values. The estimated values are presented as contour maps. The pattern of variation and the underlying possible processes for the variation are discussed. The results suggest that the likely influence of spatial variation of soil properties on crop growth may have to be considered in modelling in order to simulate the real field situation

Grassland converted to cropland: Soil conditions and sorghum yield

An appropriate tillage system is needed for conversion of virgin lands or revegetated lands to croplands to ensure sustainable crop production. We compared the effects of three tillage systems (viz. primary tillage with sweep implement (SW), moldboard plough (MB), and no-tillage NT)) on grain sorghum (Sorghum bicolor (L.) Moench) yield and some soil properties. The land had been used for growing mainly Blue grama grass (Bouteloua gracilis) and Buffalograss (Buchloe dactyloides) for over 50 years. A split-plot field experiment with SW, MB, and NT as main plots was conducted on a Pullman clay loam (Torrertic Paleustolls). Sub-plot treatments were (a) increased soil water content at planting by adding 114 mm of water (PW +), and (b) existing soil water content at planting (PW −). Because of the surface mulch, more soil water was stored in the NT treatment than in either the SW or MB treatments. The increased stored water was also reflected in greater grain and stover yields for NT sorghum. Peak water extracted from soil by crop, as estimated from soil water content measurements, occurred during the vegetative stage at 60 days after emergence (DAE). It was greatest for NT sorghum, followed in order by SW and MB. Although grain and stover yields were larger with NT than with SW or MB, grain and stover from MB plots contained more nitrogen than those from SW and NT plots. Soil organic carbon content at a depth of 0–15 cm was significantly greater (P < 0.05) under NT (1.40%) than under SW (1.21%) or MB (1.25%). Ploughing increased soil nitrogen mineralization, with the result that NO3−-N at a depth of 0–15 cm was larger under MB than under NT. The NH4+-N content under the three tillage systems was highly variable. From a production viewpoint, a no-tillage system is better than MB or SW for converting revegetated land to cropland in locations where soil water is limiting

A modified contour bunding system for Alfisols of the semi-arid tropics

Contour bunding is the most widely practised soil conservation measure on Alfisols of the semiarid tropics in India. The conventional contour bund system allows water to stagnate for long periods in extensive areas along the bunds that affects crop yields in these areas. Crop yields from sorghum/pigeon pea intercrop and pearl millet/pigeon pea intercrop at different distances from the bunds were measured to demonstrate the effects of bunding. The effects of eroded sediment deposition on the infiltration behavior of the zone near the bunds are also discussed. A modified contour bunding system with gated outlets is described. Contour bunds with gated outlets were found to ensure adequate control of runoff and soil loss. Crops grown in the fields bunded by gated outlets yielded better than those grown in fields surrounded by conventional bunds. The water balance of the ponded areas near the bunds is presented for both the modified and conventional contour bunding system

A Runoff Model for Small Watersheds in the Semi-Arid Tropics

A modified Soil Conservation Service (SCS) runoff model and a soil moisture accounting procedure were used to simulate runoff for small watersheds. The validity of the model and the moisture accounting procedure were tested using hydrological data collected from small Vertisol watersheds at ICRISAT Center in India. The agreement between measured and simulated daily, monthly, and annual runoff was good. The root mean square error values between the measured and simulated annual, monthly, and daily runoff from a Vertisol watershed were 5.2, 3.1, and 1.6 mm, respectively. The modified model and the moisture accounting procedure simulated quite accurately runoff for high, low as well as normal rainfall years in the semi-arid environment

Tillage systems and soils in the semi-arid tropics

Even though conservation tillage may be ideal for the semi-arid tropics (SAT) in view of results from studies and tillage practices in the U.S.A. and Australia, studies conducted in semi-arid regions of Africa appear to support the use of conventional tillage systems. Some of the reasons for this apparent discrepancy are because of the physical properties of the soils in semi-arid Africa, particularly the Sahelian zones where the soils are sandy, have high bulk densities and therefore low total porosities and form crusts upon wetting and drying. Consequently, no-till or reduced tillage systems that do not have the soil surface covered by residue in irder to prevent formation of crust as a result of raindrop impact, tend to lose water through runoff in a region where water economy is essential. Also, because these soils have inherently high bulk densities, conventional tillage systems appear to be suitable since they increase the macropores, reduce both bulk density and strength and thus ensure prolific root distribution and the resultant exploration of water and nutrients at greater soil depths. Notwithstanding, it seems that since most of the SAT soils are structurally unstable, further conventional tillage even though it has ephemeral advantages, may in the long term be exacerbating the problems of structural instability and their deleterious effect on water and soil conservation and therefore on crop production. We suggest that at this stage soil tillage research in the semi-arid regions of Africa and Asia should re-examine some of the concepts of conservation tillage in relation to soil physical properties and processes in order to obtain a tillage system that ensures high crop yields without destruction of the soil resource

Measuring soil processes in agricultural research

Soil and crop management strategies (e.g., tillage, bunding, cropping intensity, and crop sequencing) are location- and season-specific in the way they affect soil processes and resource utilization by crops. Research findings on these effects therefore need to be modeled if they are to be extrapolated to other locations wi th similar soils and climatic conditions. This manual presents practical methods for assessing management effects on such soil processes as water infiltration and erosion by water, and on water, air, and nutrient use by crops. It covers the basic elements of soil physical characterization, and deals principally with the role of soil structure on water infiltration and percolation, heat flow, aeration, and the mobility of roots and soil microorganisms. The authors discuss the agronomic and engineering practices that affect soil processes; and the effects of such strategies as contour cultivation, organic and inorganic amendments, watershed management, and soil surface manipulations are emphasized