Simulated nitrate leaching in annually cover cropped and perennial living mulch corn production systems

Abstract

Corn (<i>Zea mays</i>) grown in the southern Piedmont requires 200 to 280 kg nitrogen (N) ha⁻¹ annually and requires up to 0.87 cm of water per day, making groundwater systems susceptible to nitrate (NO₃⁻) leaching. A perennial white clover (<i>Trifolium repens</i> L.) living mulch (LM) system may reduce NO₃-N leaching by using legume N to replace mineral N, though little information is available on such a system in the southern Piedmont. Therefore, a HYDRUS-1D model was used to simulate water and NO₃-N flux in three cover crop systems. Cereal rye (<i>Secale cereal</i> L.) (CR), crimson clover (<i>Trifolium incarnatum</i> L.) (CC), and a white clover LM were fertilized with 280, 168, and 56 kg N ha⁻¹. The HYDRUS-1D model was calibrated and validated with observed water contents and NO₃-N data that were collected over two years. Water and NO₃-N flux models were created for each treatment and evaluated using coefficient of determination, percentage bias, and index of agreement, and showed good agreement to observed data. Nitrate leaching below 1 m in 2015/2016 was 23.5, 12.7, and 21.4 kg ha⁻¹ for the CC, LM, and CR treatments, respectively, but was less than 1 kg ha⁻¹ for all treatments in 2016/2017 due to prolonged drought. Differences in leached NO₃-N among treatments were attributed to variation in mineral N application rate and NO₃-N uptake by cover crops. Overall, results suggest that the use of a perennial LM system may reduce NO₃-N leaching when compared to annual CC and CR cover crop systems.