CROPPING SYSTEM EFFECTS ON INTERRILL SOIL LOSS IN THE GEORGIA PIEDMONT

Differential soil development and erosion in the southern Piedmont have resulted in surface horizons with variable thickness. Tillage has degraded these surface horizons and has mixed varying proportions of clayey B horizon into the plow layer, leaving soil surfaces with differing properties within the same or similar soil series. To test the effectiveness of three cropping systems in reducing interrill soil loss from these landscapes, simulated rainfall was applied to three sites of Typic Kanhapludults with differing surface horizon thickness and clay content. Each site contained plots that had been managed under conventional-tilled monocrop soybean (Glycine max [L.] Merr.), conventional-tilled monocrop grain sorghum (Sorghum bicolor [L.] Moench), and no-till double-cropped crimson clover (Trifolium incarnatum L.) and grain sorghum for 5 yr. Before tillage of the sites (consolidated state) and with residue from the previous years crop left on the surface, interrill soil loss from the no-till grain sorghum was only 12% of that from conventionally tilled soybean. Soil loss from conventionally tilled grain sorghum was 63% less than from conventionally tilled soybean. When residue was removed from the consolidated surface, soil loss from all treatments increased, and no difference in soil loss was found between the two conventionally tilled cropping systems. The no-till treatment, however, had 70% less soil loss than the conventionally tilled systems. The reduction in soil loss under no-till with residue removed from the surface was attributed to a mean increase in organic C from 10 to 23 g kg-1 and a mean increase of water-stable aggregates from 51 to 87% in the 0- to 0.015-m layer that were induced by no-tillage. After tillage of the conventional-tilled plots, interrill soil loss increased by about 45%, compared with the consolidated soils. This increase in soil loss is attributed to increased detachability of the soil after tillage. With residue removed, the three sites had similar amounts of runoff and soil loss. These results indicate that modification of surface soil properties by no-till cropping systems is an important factor influencing runoff and interrill-soil-loss reductions observed with no-tillage.