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.

中文翻译：

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覆盖作物的分裂氮应用减少了地下硝酸盐的损失，同时保持了玉米产量

在许多地区，人工地下排水对于维持作物生产至关重要，但也可能通过加剧下游硝酸盐 (NO ₃ )-氮 (N) 的输送而损害水质。覆盖作物和施氮肥已被推广为减少 NO ₃ -N 损失的关键保护措施，但很少有研究同时评估它们对水质和作物生产力的影响。进行了一项田间研究，以评估施氮时间和覆盖作物对连续玉米 ( Zea mays L.)地下排水 NO ₃ -N 损失和谷物产量的影响。处理是种植前-N：224 kg N ha ^–12018 年分批应用 60% 下降 + 40% 种植前应用，或在 2019 年和 2020 年作为单一种植前应用；split-N：40% 植前 + 60% 侧裙 (V6–V7)；split-N + 覆盖作物 (CC)：Split-N + 谷物黑麦 ( Secale creame L.)；和零 N 图作为控制。在 3 年的研究期间，与种植前 N 相比，split-N + CC 显着降低了流量加权的 NO ₃ –N 浓度和 NO ₃ –N 损失，分别降低了 35% 和 37%。然而，使用分裂 N 的流量加权 NO ₃ –N 浓度（4.3 mg L ^–1）和 NO ₃ –N 损失（22.4 kg ha ^–1）与种植前 N（4.8 mg L ^–1和26.4 公斤公顷^–1，分别）或 split-N + CC（分别为 3.1 mg L ^–1和 16.7 kg ha ^–1）。玉米产量在对照处理中显着降低，但在任何年份施氮处理之间均无差异。这些结果表明，将裂氮施用与覆盖作物相结合有望实现到 2025 年实现全州临时里程碑 NO _{3 –} N 减少 15% 的目标，而不会对作物生产力产生负面影响。