NITRATE LEACHING TO A SHALLOW MID-ATLANTIC COASTAL-PLAIN AQUIFER AS INFLUENCED BY CONVENTIONAL NO-TILL AND LOW-INPUT SUSTAINABLE GRAIN PRODUCTION SYSTEMS

In December, 1987, the states in the Chesapeake Bay region, along with the federal government, signed an agreement which called for a 40% re duction in nitrogen and phosphorus loadings to the Bay by the year 200 0. To accomplish this goal major reductions in nutrient loadings assoc iated with agricultural management practices were deemed necessary. Th e objective of this study was to determine if reducing fertilizer inpu ts to the NT system would result in a reduction in nitrogen contaminat ion of groundwater. In this only, groundwater, soil, and percolate sam ples were collected from two cropping systems. The first system was a conventional no-till (NT) grain production system with a two-year rota tion of corn/winter wheat/double crop soybean. The second system, deno ted low-input sustainable agriculture (LISA), produced the same crops using a winter legume and relay-cropped soybeans into standing wheat t o reduce nitrogen and herbicide inputs. Nitrate-nitrogen concentration s in groundwater were significantly lower under the LISA system. Over 80% of the NT groundwater samples had NO3-N concentrations greater tha n 10 mgl-1, compared to only 4% for the LISA cropping system. Signific antly lower soil mineral N to a depth of 180 cm was also observed. The NT soil had nearly twice as much mineral N present in the 90-180 an p ortion than the LISA cropping system.