EFFECTS OF TILLAGE AND RAINFALL ON SOIL SURFACE-ROUGHNESS AND PROPERTIES

The effects of tillage and rainfall on soil surface changes were investigated by subjecting ploughed, harrowed, rolled, and untilled plots of a silt loam soil (Typic Hapludalf) to five 150-min simulated rainstorms. The storms were applied every 24 hours at a constant rain intensity of 70 mm.h-1. The soil parameters studied were random roughness, bulk density, and total porosity. After 875 mm of rainfall, random roughness degraded to constant values of 3.7, 1.5, and 0.8 cm below the initial values for the ploughed, harrowed, and rolled treatments, respectively. Bulk density increased by 0. 1 6, 0.26, 0.15, and 0.08 g . CM-3, While total porosity decreased by 0.08, 0.13, 0.07, and 0.03 CM3.CM-3 for the ploughed, harrowed, rolled, and untilled treatments, respectively. Ploughing produced a rough surface that withstood rainfall energy while harrowing, and rolling produced smoother and less resistant surfaces. The results showed that, under rainfall conditions similar to those studied here, a ploughed soil is likely to maintain high water storage capacity on the surface without appreciable runoff or soil loss while overtillage may have deleterious effects on both soil and water conservation. Regression equations to predict changes in surface roughness, bulk density, and total porosity due to rainfall were developed. The equations can be incorporated in soil water balance and hydrological models for cultivated fields.