The Soil and Water Assessment Tool (SWAT) was used 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 showed 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 during the fallow season 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.

This work is published in Rath S. , M. Zamora-Re, W. Graham, M. Dukes, and D. Kaplan, 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, Agricultural Water Management. https://doi.org/10.1016/j.agwat.2020.106634 , 2021.

Experimental data used to calibrate and validate the model is archived at Zamora-Re, M., J. Merrick, M. Dukes (2021). Floridan Aquifer Collaborative Engagement for Sustainability (FACETS) – Field trial data from Live Oak, Florida. Ag Data Commons. https://doi.org/10.15482/USDA.ADC/1521079.