ABSTRACT
The parent material of soils, extent of weathering, characteristics like bulk density, texture, structure, aeration, precipitation pattern and soil moisture conditions dictate various physicochemical aspects of soil that have direct bearing on nutrient dynamics in the agroecosystem. The physicochemical properties of each soil type markedly influences nutrient dynamics in the profile and cropping system. Regarding soil structure, it is difficult to define the most appropriate characteristics. Soils should be crust free, loamy and congenial for rapid root growth. A well-aggregated soil contains aggregates of 1-5 mm size in dry and wet conditions. Soil aggregation could be improved by adopting suitable mulching and organic matter supplements. For example, recycling straw in the dry lands is known to improve both size and percentage aggregates. The in situ decomposition of sorghum residues improved soil aggregates to 0.38 mm compared to 0.11 mm in control. The infiltration rate improved from 2.59 cm/hr in control plots to 4.75 cm/hr in straw treated fields and to 8.10 cm/hr in legume haulm treated fields. The bulk density of soil affects root proliferation in the profile. Root penetration and activity is least in soils with bulk density 1.8 or above. The mechanical impedance to root spread is high. Presence of high bulk density subsurface layers restricts infiltration of water and root penetration. Hence, deep tillage and chiseling up to 20 cm or below is beneficial in the dry lands. High bulk density is uncongenial to sorghum root growth, moisture infiltration and nutrient availability. The percentage of pores > 0.5 mm in diameter decreases as bulk density increases. Further, hydraulic conductivity and water diffusivity reduced due to high bulk density. Hence, infiltration of water and nutrients to root lessened. Vertical mulches are known to improve water infiltration and nutrient conservation. Run off and soil erosion also affects soil nutrient conservation. The subsoil salinity is yet another factor that affects chemical transformations, nutrient availability and finally it reduces mineral acquisition rates by crops grown on Vertisols. A major share of the explanations on soil physicochemical properties, reactions and nutrient availability are drawn from several publications [1-4].
