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

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.