Quantifying nitrate leaching to groundwater from a corn-peanut rotation under a variety of irrigation and nutrient management practices in the Suwannee River Basin, Florida

Abstract

Nitrate leaching from agricultural fields is a significant contributor of groundwater pollution globally, threatening drinking water resources and downstream ecosystems. Quantifying nitrate leaching driven by variable climate, soils, and management practices is challenging, but it is critical for developing sustainable agricultural production systems. While irrigation and fertilizer “best management practices” (BMPs) have been widely implemented to reduce agricultural nitrate leaching, their ability to meet environmental protection goals remains uncertain. In this study, we used the Soil and Water Assessment Tool (SWAT) to simulate crop yields and nitrate leaching for corn-peanut rotations under a variety of nutrient and irrigation management practices in the Suwannee River Basin (Florida), where groundwater feeds springs that are protected by a federally mandated nutrient criteria of 0.35 mg/L Nitrate-Nitrogen (NO3-N). Data from a field experiment of nine irrigation and nitrogen (N) management treatments were used to calibrate SWAT, with good to excellent results (Nash Sutcliffe Efficiencies from 0.72 to 0.97 for soil moisture, 0.85–0.96 for crop yield, 0.48–0.96 for crop N uptake, and 0.15–0.82 for soil nitrate). The calibrated model was then used to quantify differences in crop yields, irrigation applied and nitrate leaching among practices over a range of historical weather. Soil moisture sensor-based irrigation with 246 kg N/ha for corn and 0 kg N/ha for peanut had no statistical difference in yields compared to common practices in the region (calendar-based irrigation, fertilization of 336 kg N/ha corn and 17 kg N/ha peanut), while reducing N leaching by 40% and irrigation applied by 45% (reductions of ~70 kg N/ha/yr and ~300 mm/year, respectively). Planting a rye cover crop reduced leaching by an additional ~50 N/ha/yr for all treatments. These results show the potential for widespread adoption of nutrient and water conservation practices to achieve the reductions in NO3-N load needed to meet environmental and regulatory goals without impacting crop yields.