Split-nitrogen application with cover cropping reduces subsurface nitrate losses while maintaining corn yields

Artificial subsurface drainage is essential to sustain crop production in many areas but may also impair water quality by exacerbating nitrate (NO₃)–nitrogen (N) delivery downstream. Cover crops and split-N application have been promoted as key conservation practices for reducing NO₃–N losses, but few studies have simultaneously assessed their effect on water quality and crop productivity. A field study was conducted to evaluate the effects of N application timing and cover crops on subsurface drainage NO₃–N losses and grain yield in continuous corn (Zea mays L.). Treatments were preplant-N: 224 kg N ha^–1 split-applied with 60% fall + 40% preplant in 2018, or as single preplant applications in 2019 and 2020; split-N: 40% preplant + 60% side-dress (V6–V7); split-N + cover crop (CC): Split-N + cereal rye (Secale cereale L.); and a zero N plot as the control. Across the 3-yr study period, split-N + CC significantly reduced flow-weighted NO₃–N concentration and NO₃–N loss by 35 and 37%, respectively, compared with preplant-N. However, flow-weighted NO₃–N concentration (4.3 mg L^–1) and NO₃–N loss (22.4 kg ha^–1) with split-N were not significantly different from either preplant-N (4.8 mg L^–1 and 26.4 kg ha^–1, respectively) or split-N + CC (3.1 mg L^–1 and 16.7 kg ha^–1, respectively). Corn yield was significantly lower in the control treatment but did not differ among N fertilized treatments in any year. These results indicate that combining split-N application with cover crops holds promise for meeting the statewide interim milestone NO₃–N reduction target of 15% by 2025 without negatively impacting crop productivity.