Tillage effects of surface and groundwater quality in loessial upland soybean watersheds

Evaluation of tillage practices on surface and subsurface water quality is essential for conserving and protecting the nation's soil and water resources. The objective of this research was to evaluate the water quality of perched groundwater (0.15 to 3.04 m) and surface runoff from a 2.13 ha no-till and a 2.10 ha conventional-till soybean watershed for plant nutrients during the 1990-1993 water years. Mean nitrate-N concentrations for all groundwater depths and sites of the no-till and conventional-till watersheds were 4.81 and 5.98 mg.L-1, respectively. Shallow groundwater NO3-N concentrations for some storms exceeded U.S. Drinking Water Standards. However, in a forested riparian zone, only 61 m down slope from the conventional-till watershed, the mean NO3-N concentration in groundwater was only 0.29 mg.L-1. Higher nutrient concentrations in surface runoff from the no-till watershed reflect the lack of sediment to sorb soluble PO4-P as well as the leaching of crop and weed residues. Despite greater runoff from the conventional-till watershed, soluble nutrient losses were generally similar from the no-till watershed due to the higher nutrient concentrations. Nutrient concentrations in surface runoff from both watersheds peaked a few days after a broadcast application of 0-20-20 and decreased during subsequent storms. Alterntive methods of fertilizer application are needed to reduce nutrient concentrations in surface runoff