TILLAGE EFFECTS ON SURFACE AND GROUNDWATER QUALITY IN LOESSIAL UPLAND SOYBEANWATERSHEDS

Abstract

Evaluation of tillage practices on surface and subsurface water quality is essential for conserving andprotecting the nations soil and water resources. The objective of this research was to evaluate the water quality ofperched groundwater (0.15 to 3.04 m) and surface runoff from a 2.13 ha no-till and a 2.10 ha conventional-till soybeanwatershed for plant nutrients during the 1990-1993 water years. Mean nitrate-N concentrations for all groundwaterdepths and sites of the no-till and conventional-till watersheds were 4.81 and 5.98 mgL1, respectively. Shallowgroundwater NO3-N concentrations for some storms exceeded U.S. Drinking Water Standards. However, in a forestedriparian zone, only 61 m down slope from the conventional-till watershed, the mean NO3-N concentration in groundwaterwas only 0.29 mgL1. Higher nutrient concentrations in surface runoff from the no-till watershed reflect the lack ofsediment to sorb soluble PO4-P as well as the leaching of crop and weed residues. Despite greater runoff from theconventional-till watershed, soluble nutrient losses were generally similar from the no-till watershed due to the highernutrient concentrations. Nutrient concentrations in surface runoff from both watersheds peaked a few days after abroadcast application of 0-20-20 and decreased during subsequent storms. Alternative methods of fertilizer applicationare needed to reduce nutrient concentrations in surface runoff.