Drainage conditions influence corn-nitrogen management in the US upper midwest

Soil drainage is not considered in the N fertilizer guidelines for corn (Zea mays L.) in the US Midwest. This study investigated the influence of soil drainage on corn grain yield, N requirement, and residual soil N, and evaluated the utility of in-season soil N measurements to guide N application. This 6-year study in Minnesota, US on a corn–soybean (Glycine max [L.] Merr.) rotation had drained and undrained conditions and six at planting (PL) (0–225 in 45 kg N ha⁻¹ increments) and four split (SP) N fertilizer rates (at planting/V6-V8—45/45, 45/90, 45/135, 45/179 kg N ha⁻¹). The drained compared to undrained soil produced 8% more grain yield (12.8 vs. 11.9 Mg ha⁻¹), 12% more N uptake (169 vs. 151 kg N ha⁻¹), 16% lower optimal N rate (ONR) (160 vs. 193 kg N ha⁻¹), 3.1% greater grain yield at ONR (13.5 vs. 13.1 Mg ha⁻¹), and similar in season and residual soil N. Compared to SP, PL lowered ONR (151 vs. 168 kg N ha⁻¹) in drained soils, and the opposite occurred for undrained soils (206 vs. 189 kg N ha⁻¹). These results substantiate the agronomic benefits of artificial drainage and the need to incorporate drainage conditions into N management guidelines.