Nutrient and pesticide concentrations in shallow groundwater (3m) and surface runoff were determined for conventional-till (CT) and no-till (NT) soybean watersheds. Groundwater NO3N concentrations were similar for both tillage systems, averaging about 7-8 ppm, but exceeded 10 ppm for some storms. Annual mean groundwater NO3N concentrations were only 0.34 ppm in a riparian zone downslope from the CT watershed. Higher nutrient concentrations in NT surface runoff reflected surface residue leaching. Runoff from both watersheds, 2 days after a broadcast application of 0-20-20, had high nutrient concentrations that decreased during subsequent storms. Pesticide concentrations in groundwater of the NT watershed were as high as 250 ppb at a depth of 1.5 m within 1 week after application (1st rainfall). Concentrations beneath the CT watershed were < 10 ppb maximum. One month after application, pesticide concentrations in groundwater beneath both watersheds had decreased to about 10% of their respective 1-week values. Similar total pesticide losses in runoff occurred for both tillage systems. NT reduced sediment loss but increased pesticide movement into the soil profile. Results of companion studies with corn at another site indicated similar trends for nutrients and pesticides in shallow groundwater. Within 11 months after application, herbicides were still detectable at very low concentrations (<1 ppb). Soil insecticides, applied at planting, were not found in groundwater. Herbicides and insecticides were detectable in both the water and sediment phases of runoff for 5 months after application. At the 1.5-m depth, the mean NO3N concentration in groundwater for conventional-, reduced-and no-till corn was 4.78 ppm compared with 6.96 ppm at the 3-m depth.
Influence of Crust Formation on Soil Porosity under Tillage Systems and Simulated Rainfall