Soil Water Dynamics and Nitrate Leaching Under Corn–Soybean Rotation, Continuous Corn, and Kura Clover

CORE IDEAS: Corn–soybean and continuous corn had similar soil water dynamics and N leaching. Urea and anhydrous ammonia resulted in similar leachate nitrate concentrations. The kura clover cropping system reduced drainage, N leaching, and fall soil N. Improving water quantity and quality impacts of corn (Zea mays L.)‐ and soybean [Glycine max (L.) Merr.]‐based cropping systems is a key challenge for agriculture in the US Midwest. Long‐term field experiments are important for documenting those effects and exploring possible solutions. This study examines differences in soil water dynamics and nitrate‐nitrogen (N) leaching among cropping systems and N fertilizer sources in a long‐term experiment in southeastern Minnesota. Drainage and leachate concentrations were measured for 4 yr using automated equilibrium tension lysimeters installed below the root zone in replicated, large plots on a well‐drained silt loam soil. Soil water storage was monitored using water content reflectometers. Corn–soybean and continuous corn cropping systems exhibited similar soil water dynamics, drainage rates (145–202 mm yr⁻¹), leachate nitrate N concentrations (21.3–25.6 mg L⁻¹), and nitrate N leaching loads (30–75 kg ha⁻¹ yr⁻¹). Nitrate‐N concentrations in the leachate were similar whether N was added as urea (21.2 mg L⁻¹) or anhydrous ammonia (25.7 mg L⁻¹). A perennial kura clover (Trifolium ambiguum M. Bieb)‐based cropping system with no N fertilizer significantly altered soil water dynamics and resulted in lower (p < 0.10) drainage rates (53 mm yr⁻¹), nitrate N concentrations (7.1 mg L⁻¹), and nitrate N leaching loads (2–5 kg ha⁻¹ yr⁻¹) compared with corn–soybean or continuous corn, but also reduced corn grain yields. These impacts are generally consistent with a growing body of literature showing substantial environmental benefits of a kura clover living mulch system for corn production, but the economic viability of such a system is not yet proven.