Studies on crusting in a kaolinitic soil from Zimbabwe and effect of different conditioners

Raindrop impact energy and clay dispersion are known to promote crust formation in many soils Appropriate management practices and/or application of high to rue strength electrolytes or polycations have been suggested lo reduce soil susceptibility to crusting On this basis, the effects of gypsum, basic Al porychlorosulfate. and iron sulphate on a Rhodic-Kandiustalf soil from Zimbabwe were studied, on small runoff plots. Other plots were prepared from untreated soil (control), mulched surface and material from the Bt horizon replacing the lop 15 cm of the Ap horizon All conditioners had similar effects in reducing runoff in comparison with the control (15% and 30% respectively for storms of moderate intensity) Runoff from all conditioner plots increased with time and intensity of rainfall approaching the control values Bt material significantly reduced runoff in comparison lo the conditioners The effectiveness of mulching (constant runoff about values of 5%) emphasises the importance of raindrop impact on the disintegration of soil aggregates Laboratory investigations suggested that clay content, formation of phosphate-metal complexes, and presence of low molecular weight humic substances also contributed substantially to crust formation.