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

Abstract

Corn (Zea mays) 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 (Trifolium repens 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 (Secale cereal L.) (CR), crimson clover (Trifolium incarnatum 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.