Aggregate Stability, Surface-Water Runoff, and Soil Loss in Wheat-Sunflower and Corn-Soybean Rotations.

Developing improved management options that limit soil erosion requires a greater understanding of the interactions between crop rotation, residue management, and precipitation patterns. We conducted a six-year study to evaluate how seasonal variation in aggregate stability, ground cover, soil moisture, and other factors affected surface-water runoff and soil loss during the growing season in both phases of corn-soybean and wheat-sunflower rotations. There was no significant difference in the mean weight diameter of dry aggregates among crops when sampled during the growing season. Soil cropped to corn following soybean, however, exhibited significantly greater aggregate breakdown during wet sieving than did soil cropped to wheat, sunflower, and soybean. Aggregate breakdown decreased with increasing surface residue biomass and increasing soluble sugars (mass/area) in the residue of the preceding crop. In field rainfall simulations, water runoff increased with increasing surface soil moisture. Potential runoff and soil loss from relatively high-intensity storms during the growing season tended to be least for wheat following sunflower and greatest for corn following soybean and sunflower following wheat. Soil loss decreased with decreasing aggregate breakdown, increasing canopy+residue cover, and increasing residue biomass from the preceding crop. We observed no differences in water runoff or soil loss due to crop rotation, but most of the soil loss occurred during the corn and sunflower phases of these rotations. These results demonstrate that temporally-variant factors such as aggregate stability, soil cover, composition of crop residue, and antecedent soil moisture are important determinants of water and soil loss during relatively intense rainfall conditions. Accounting for the interactions among these factors is essential for accurate predictions of annual water and soil loss during runoff for a given crop.