EPIC model prediction of winter rye cover crop effects on crop yield and nitrate-N leaching in Minnesota

Abstract

Coarse-textured soils in central Minnesota cultivated with corn (Zea mays L.) and soybean (Glycine max L.) exhibit good productivity, however, are vulnerable to nitrate-N leaching losses. In such circumstances, winter rye (Secale cereale L.) as a cover crop may reduce nitrate-N leaching by scavenging soil nitrogen (N) in late-fall and early-spring fallow period. The Environmental Policy Integrated Climate (EPIC) model was used for decadal-scale (2010–2020) simulation of yield/biomass and nitrate-N leaching in corn– (C–C) and corn–soybean/soybean–corn (C–Sb/Sb–C) rotations, with and without winter rye, under different fertilizer N rates applied to corn (0, 100, 200, 250, and 300 kg ha⁻¹) on irrigated coarse-textured soils in central Minnesota. Model efficiency calculated based on Nash–Sutcliffe coefficient, relative root mean square error, and R² statistics indicate that EPIC assessment for calibration and validation treatments was excellent-good for corn/soybean yield, and good-satisfactory for rye biomass and NO₃-N leaching losses. Results indicate that N fertilizer rates up to 250 kg N ha⁻¹ applied to corn had a positive impact on rye biomass; however, large crop-rotation and climate-induced variations were observed. Annual nitrate-N leaching losses at maximum return to nitrogen rates at a 0.05 N price to crop value ratio for corn under C–C (250 kg N ha⁻¹) and C–Sb/Sb–C (200 kg N ha⁻¹) with no-rye averaged 61.5, 47.4, and 41.8 kg ha⁻¹, while grain yield averaged 12.5, 12.3, and 4.0 t ha⁻¹ for corn (C–C), corn (C–Sb/Sb–C), and soybean (C–Sb/Sb–C), respectively. Planting rye under these rotations gave annual average reductions in nitrate-N losses relative to corresponding no-rye treatments of 2.9 (4.7%), 3.4 (7.3%), and 6.5 kg ha⁻¹ (15.6%), with rye N uptake of 10.3, 12.1, and 33.5 kg ha⁻¹; and rye biomass production of 0.61, 0.74, and 2.0 t ha⁻¹, respectively. EPIC assessment indicates that winter rye as cover crop did not negatively impact the subsequent corn/soybean yield and proved to be an effective strategy for reducing nitrate-N losses, particularly following the soybean crop.