TILLAGE EFFECTS ON SURFACE AND GROUNDWATER QUALITY IN LOESSIAL UPLANDSOYBEAN WATERSHEDS

Evaluation of tillage practices on surface and subsurface water qualit y is essential for conserving and protecting the nation's soil and wat er resources. The objective of this research was to evaluate the water quality of perched groundwater (0.15 to 3.04 m) and surface runoff fr om 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 c oncentrations 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 c oncentration in groundwater was only 0.29 mg.L-1. Higher nutrient conc entrations in surface runoff from the no-till watershed reflect the la ck of sediment to sorb soluble PO4-P as well as the leaching of crop a nd weed residues. Despite greater runoff from the conventional-till wa tershed soluble nutrient losses were generally, similar from the no-ti ll watershed due to the higher nutrient concentrations. Nutrient conce ntrations in surface runoff from both watersheds peaked a few days aft er a broadcast application of 0-20-20 and decreased during subsequent storms. Alternative methods of fertilizer application are needed to re duce nutrient concentrations in surface runoff.