TILLAGE STUDIES WITH A CORN SOYBEAN ROTATION - HYDROLOGY AND SEDIMENT LOSS

When soybean [Glycine mar (L.) Merr.] is produced on sloping fields using conventional tillage and mechanical cultivation for weed control, potential soil losses are high, limiting production to relatively flat lands. With the advent of conservation tillage practices and herbicides for weed control, soybean production with tolerable soil losses on sloping fields has become technically possible. To evaluate soil loss under these new conditions, runoff and erosion were measured on six small watersheds that were farmed for 6 yr in a corn (Zea mays L.)-soybean rotation with conservation tillage. Two of the watersheds were chiseled each year, two others paraplowed, and the other two received no-tillage. A rye (Secale cereale L.) cover crop was established each winter following soybean. With average yearly rainfall of 930 mm, yearly runoff was 63.5 mm and varied between 28 and 108 mm. Average yearly soil loss for the 6-yr period was 526 kg/ha, < 10% of the allowable soil loss. Two storms caused most of the erosion, with a single storm accounting for 42% of the total measured soil loss. Earlier, these same watersheds averaged 5750 kg/ha of measured soil loss during the corn years of a corn-wheat-meadow-meadow rotation with conventional tillage.