SOIL SURFACE MODIFICATION BY BIOMASS INPUTS AFFECTING RAINFALL INFILTRATION

The quantity, kind, and method of applying organic materials to the soil in crop culture are known to have a major effect on surface characteristics. To determine the effectiveness of selected crop biomass inputs on soil surface characteristics that significantly impact rainfall infiltration, sites on slightly, moderately, and severely eroded classes of Cecil-Pacolet soils (clayey, kaolinitic, thermic Typic Kanhapludults) were selected. On each class of erosion, soybean [Glycine mar (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] were each planted into a disk-harrowed seedbed following winter fallow in each of 5 yr. Grain sorghum was also no-till-planted into a crimson clover (Trifolium incarnatum L.) cover crop. Each summer crop was grown both under irrigation and natural rainfall. The average water stability of aggregates in the 0- to 15-mm layer of the no-till-planted grain sorghum into clover was 53 and 44% greater than the tilled plantings of grain sorghum and soybean, respectively. Only at > 0.8 kg kg-1 aggregate stability was correlated with soil C content. In contrast, regressions of water-stable soil aggregates on the natural log of cumulative stover after 5 yr of treatment yielded r2 values of 0.81 to 0.99. Soil-incorporated soybean stover was distinctly least effective in developing water-stable soil aggregates in the surface 1.5 cm. The effect of increased soil surface aggregate stability was reflected in a soil water pressure greater than -0.1 MPa in the surface 0.5 m for a significantly greater fraction of the summer growing season and in increased infiltration. The infiltration mte after residue removal was 100% greater on the grain sorghum no-till planted into clover than grain sorghum planted into a tilled seedbed. The soil modifications that produced a very significant change in rate of infiltration were obtained in 4 or 5 yr by a no-till culture that provides about 12 Mg ha-1 yr-1 of decomposing crop residue on the soil surface.