Nitrate and Chloride Loading to Groundwater from an Irrigated North-Central U.S. Sand-Plain Vegetable Field
2001
Stites, W. | Kraft, G.J.
Groundwater pollution and associated effects on drinking water have increased with the expansion of irrigated agriculture in north-central U.S. sand plains. Controlling this pollution requires an ability to measure and predict pollutant loading by specific agricultural systems. We measured NO₃ and Cl loading to groundwater beneath a Wisconsin central sand plain irrigated vegetable field using both a budget method and a new monitoring-based method. By relying on frequent monitoring of shallow groundwater, the new method overcomes some limitations of other methods. Monitoring-based and budget methods agreed well, and indicated that loading to groundwater was 165 kg ha⁻¹ NO₃–N and 111 kg ha⁻¹ Cl for sweet corn (Zea mays L.) in 1992, and 228 kg ha⁻¹ NO₃–N and 366 kg ha⁻¹ Cl for potato (Solanum tuberosum L.) in 1993. Nitrate N loading was 56 to 60% of available N, or 66 to 70% of fertilizer N. Sweet corn NO₃ loading was about typical for this region, but potato NO₃ loading was probably 50% greater than typical because heavy rains provoked extra fertilizer application. Our results imply that typical NO₃–N loading would be 119 kg ha⁻¹ for sweet corn and 203 kg ha⁻¹ for potato, even with strict adherence to University Extension fertilizer recommendations. To keep average groundwater NO₃–N within the 10 mg L⁻¹ U.S. drinking water standard, each irrigated vegetable field would need to be offset by five to eight times as much land supplying NO₃–free groundwater recharge.
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