Cover crop species and termination date could affect fertilizer-nitrogen (N) management and N diagnostic methods traditionally used in bare fallow-maize (Zea mays L.) systems. Our objectives were to (a) assess the effect of cover crop termination date on maize yield and response to fertilizer-N, (b) determine maize yield at varying N rates following different cover crop species and mixtures, and (c) evaluate the chlorophyll meter reading (CMR), grain N concentration (N_c), and grain N nutrition index (NNI) as N diagnostic methods. Experiments were conducted at four sites in the southeastern Argentinean Pampas with maize planted after cover crops. Factors investigated were cover crops with vetch (Vicia villosa Roth), vetch–oat (Avena sativa L.) mixture, or bare fallow; early termination of cover crops or ∼3 wk later; and maize fertilizer-N at 0, 50, 100, and 200 kg N ha^–1. The minimum N rate that maximized grain yield was higher in vetch–oat mixture (100 kg N ha^–1) than in vetch (50 kg N ha^–1). Maize yield was not affected by cover crops with 200 kg N ha^–1. Late termination dates of vetch–oat mixture reduced maize yield by 15% compared with early termination dates, while there was no effect of vetch termination date. Cover crop termination date did not affect yield response to fertilizer-N. Relative CMR at silking, grain N_c, and especially grain NNI at maturity were useful tools to diagnose maize N status and cover crop effect. Cover crop management should be considered to adjust the fertilizer N rate and optimize maize productivity.

中文翻译：

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覆盖作物物种可以增加或减少玉米的肥料氮需求

覆盖作物种类和终止日期可能会影响传统上用于裸露休耕玉米 ( Zea mays L.) 系统的肥料-氮 (N) 管理和氮诊断方法。我们的目标是 (a) 评估覆盖作物终止日期对玉米产量和对氮肥反应的影响，(b) 确定不同覆盖作物物种和混合物后不同 N 比率下的玉米产量，以及 (c) 评估叶绿素米读数 (CMR)、谷物 N 浓度 (N _c ) 和谷物 N 营养指数 (NNI) 作为 N 诊断方法。在阿根廷潘帕斯东南部的四个地点进行了试验，在覆盖作物后种植玉米。调查的因素是用紫云英 ( Vicia villosa Roth)、紫云英燕麦 ( Avena sativa )覆盖作物L.) 混合物，或裸露的休耕；提前终止覆盖作物或 ∼3 周后；0、50、100 和 200 kg N ha ^–1的玉米肥料-N 。使谷物产量最大化的最小氮肥用量在野豌豆-燕麦混合物（100 kg N ha ^-1）中高于在野豌豆（50 kg N ha ^-1）中。玉米产量不受 200 kg N ha ^–1覆盖作物的影响。与提早终止日期相比，野豌豆-燕麦混合物的延迟终止日期使玉米产量降低了 15%，而野豌豆终止日期没有影响。覆盖作物终止日期不影响对氮肥的产量反应。出丝时的相对 CMR，晶粒 N _c，尤其是成熟的谷物 NNI 是诊断玉米氮素状况和覆盖作物效应的有用工具。应考虑覆盖作物管理以调整施氮量并优化玉米生产力。