Design of a field-scale approach for evaluating nitrogen management practices impacts to groundwater

While nitrogen fertilizers and other nutrient sources (e.g., manure, bio-solids, and legume credits) are valued for their ability to increase crop yields, a portion of nitrogen applied through these methods leaches to groundwater as nitrate. Nitrate in Wisconsin’s groundwater is a pervasive drinking water contaminant and nitrate exported to surface waters via groundwater contributes to eutrophication and hypoxic conditions in the Gulf of Mexico. Demonstrating through on-farm research what baseline nitrate concentrations can be expected for a given region and under well managed fields is the first step in the setting of achievable water quality goals and prioritizing nitrogen reduction strategies.

This study investigated the utility of a field-based approach for the evaluation of nitrogen management strategies and effects on nitrate concentrations in groundwater. We set out to 1) characterize spatial variability of groundwater nitrate below agricultural fields 2) evaluate seasonal differences in nitrate concentrations at the top of the water table (fall versus spring). 3) provide an evaluation of sampling numbers needed to characterize spatial variability and 4) describe the advantages/disadvantages of using of a geoprobe versus bucket auger for collecting water samples.