Impact of historical and current farming systems on groundwater nitrate in northern Missouri

A major objective of the Management Systems Evaluation Areas (MSEA) Project has been to assess farming system impact on NO{sub 3}-N concentrations in shallow aquifers. In Missouri our interest was to assess farming systems on the claypan soil/glacial aquifier. Three fields were selected and instrumented with groundwater wells in the spring of 1991. Wells were sampled quarterly and analyzed for NO{sub 3}-N. Average NO{sub 3}-N concentration since 1991 was 7 mg l{sup -1}, but 25% of the wells had NO{sub 3}-N in excess of 10 mg l{sup -1}. In one field, NO{sub 3} concentrations were much higher and 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 aquifier. Current farming systems are probably affecting groundwater quality, but, because of the glacial till`s apparent buffer for NO{sub 3} storage, groundwater NO{sub 3} concentration changes are slow.