IMPACT OF HISTORICAL AND CURRENT FARMING SYSTEMS ON GROUNDWATER NITRATE IN NORTHERN MISSOURI

A major objective of the Management Systems Evaluation Areas (MSEA) Pr oject has been to assess farming system impact on NO3-N concentrations in shallow aquifers. In Missouri our interest was to assess farming s ystems on the claypan soil/glacial aquifer. Three fields were selected and instrumented with groundwater welts in the spring of 1991. Wells were sampled quarterly and analyzed for NO3-N. Average NO3-N concentra tion since 1991 was 7 mg l(-1), but 25% of the wells had NO3-N in exce ss of 10 mg l(-1). In one field, NO3 concentrations were much higher a nd are still decreasing after apparently receiving excess nitrogen (N) from manure and N fertilizer before 1980. Long-term N management has long-term impacts on groundwater quality in this aquifer. Current farm ing systems are probably affecting groundwater quality: but, because o f the glacial till's apparent buffer for NO3 storage, groundwater NO3 concentration changes are slow.