TILLAGE STUDIES WITH A CORN-SOYBEAN ROTATION - SURFACE RUNOFF CHEMISTRY

When soybean [Glycine max (L.) Merr] is grown on sloping soils, there is a high potential for soil and nutrient losses. The purpose of this study was to compare nutrient losses in surface runoff across a range of watershed conditions when tillage practice was a variable. For 6 yr in east-central Ohio, nutrient concentrations and transport in surfac e runoff were measured from six small (< 1-ha) watersheds planted to a corn (Zea mays L.)-soybean rotation. Two watersheds were chisel plowe d each year, two were paraplowed, and two received no-tillage. Rye (Se cale cereale L.) provided winter cover following soybean harvest. Nitr ate-N and K concentrations in surface runoff were greater during corn years than soybean years, but there was no significant difference amon g tillage treatments. There were no consistent differences between cro ps or among tillage practices for the transport of soluble P, soluble K, and total organic C (TOC). Most of the NO3-N loss was in the runoff from a small percentage of runoff events. Although NO3-N concentratio ns in surface runoff frequently exceeded 10 mg/L during the corn years , the actual amount of N lost was small. But because of year-to-year v ariation in runoff, which masked most of the differences resulting fro m cropping or tillage practice, there is a need for long-term research (> 6 yr) to assess the environmental risks associated with a particul ar management practice.