EROSION AND NUTRIENT LOSSES FROM ZERO-TILLAGE ON A CLAY SOIL

Conventional tillage (CT) and zero tillage (ZT) farming systems were c ompared in terms of losses of sediment, nitrogen (N) and phosphorus (P ) in surface runoff from watersheds with heavy clay soils in central T exas, U.S.A. CT included several sequential tillage operations that re sulted in burial of most of the plant residue from the previous crop. ZT involved no primary or secondary tillage, and crops were planted th rough the residue from the previous crop. ZT had no effect on runoff a mounts but reduced the loss of sediment, N, and P relative to CT. Simi lar results were obtained for each of the three crops used in the stud y. The EPIC (Erosion-Productivity Impact Calculator) model successfull y simulated the effect of tillage on runoff, sediment, and nutrient lo ss with the exception of soluble N and P.