Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/1998
Publication Date: N/A
Interpretive Summary: By the end of this century, it is estimated that 60 to 70% of all U.S. cropland will employ some kind of conservation tillage. For much farm land, conservation tillage may be the only way to reduce soil erosion to acceptable limits. Conservation tillage has proven to minimize nonpoint contamination of surface water by reductions in runoff and erosion, but it also increases infiltration, and hence the potential for increased leaching of pesticides and fertilizers. The research presented here indicates that tillage differences, no-till, or conventional-till for soybeans, do not adversely affect the concentration of plant nutrients, specifically, nitrate-nitrogen, in shallow groundwater. For most storms, ground water nitrate-nitrogen was less than the U.S. Drinking Water Standard designed to protect against methemoglobinemia or blue baby disease. As an additional benefit, no-till soybeans reduced soil losses by as much as 95 to 98% compared to conventional-till soybeans. This information will be useful to water resources managers who deal much with surface/ground water issues and farmers who need soil and water conservation information for decision-making purposes.
Technical Abstract: Evaluation of tillage practices on surface and subsurface water quality is essential for conserving and protecting the nation's soil and water resources. 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 were sampled for plant nutrients during the 1990-1993 water years. Mean nitrate-N concentrations for all groundwater depths and sites of the no-till conventional-till watersheds were 7.05 and 5.98 mg.L**-1, respectively. Shallow groundwater NO3-N concentrations for some storms did exceed 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. Surface runoff from both watersheds a few days after a broadcast application of 0-20-20 had high nutrient concentrations that decreased during subsequent storms. Alternative fertilizer application methods are needed to reduce nutrient concentrations in surface runoff.