Effects of zero tillage and stubble retention on some properties of a cracking clay

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Abstract
Soil chemical and physical properties of a black cracking clay were measured after five years under a zero tillage and stubble retention trial. Stubble retention slightly increased the organic carbon content of the 0-10 cm layer, and the dispersion ratio of the 0-4 cm layer. Stubble retention increased dry aggregate size in the 0-4 cm layer of the zero tilled treatments, apparently due to a reduction in the rate of drying of the surface after rain. Changes in the distribution of cations in the surface soil developed in the absence of tillage, with lower exchangeable sodium percentage (ESP) and higher exchangeable potassium percentage in the 0-4 cm layer under zero tillage. The reduction in ESP in the 0-4 cm layer under zero tillage also reduced dispersion ratios. The ratio CEC : % clay for the 0-4 cm layer was reduced by zero tillage. Chloride profiles gave evidence for increased deep infiltration under zero tillage. This is attributed to the presence of cracks that were not closed by tillage.