Nitrogen fertilization affects maize grain yield through regulating ear leaf senescence and nitrogen remobilization (RemN), yet few studies focus on how nitrogen alters the onset of leaf senescence and then affects leaf RemN to regulate grain-filling. This study aimed to investigate the relationship between the onset of ear leaf senescence, ear leaf RemN, and grain-filling. A field experiment in Yancheng, China,with six nitrogen rates (0, 67.5, 136.5, 205.5, 274.5, and 343.5 kg N ha) were conducted and ear leaf senescence and grain-filling were analyzed in response to different N fertilizations. Optimal nitrogen fertilization (around 205.5 kg N ha) significantly increased grain yield (average 10359.2 kg ha) and harvest index (HI, average 0.58). Additionally, nitrogen application increased the nitrogen concentration of ear leaves and delayed senescence. The maximum delay was 3.4 days compared to the control. At the time of maximum grain yield, the onset of senescence could be delayed by 1.6–1.9 days. However, delayed senescence of ear leaves negatively impacted leaf RemN contribution to grain nitrogen, with a maximum limit of 16.0 observed at 205.5 kg N ha. Furthermore, nitrogen fertilization could reduce the maximum grain-filling rate (G), the maximum grain weight (W), and the time to reach the maximum grain-filling rate (T). Higher grain yield and its response to nitrogen relied on a shorter time interval between the onset of senescence and T. At a nitrogen fertilization rate of 196.85 kg N ha (close to the optimal rate of 205.5 kg N ha), the minimum time interval could be reduced to about 2.4 days, resulting in a maximum relative yield response to nitrogen of 39.98%. Optimal nitrogen fertilization improved grain yield by delaying the onset of senescence of ear leaves and altering its RemN, thus impacting grain filling. It provided valuable insights for achieving higher yields under the optimal nitrogen fertilization by considering the onset of ear leaf senescence, the ability of RemN in relation to grain filling.

中文翻译：

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最佳氮肥施用量可通过延缓穗叶衰老从而改变其氮素再利用来提高玉米产量

氮肥通过调节穗叶衰老和氮再动员（RemN）来影响玉米籽粒产量，但很少有研究关注氮肥如何改变叶片衰老的开始，进而影响叶片RemN以调节籽粒灌浆。本研究旨在探讨穗叶衰老发生、穗叶 RemN 与籽粒灌浆之间的关系。在盐城进行了6种施氮量（0、67.5、136.5、205.5、274.5和343.5 kg N·ha）的田间试验，分析了穗叶衰老和籽粒灌浆对不同施氮量的响应。最佳施氮量（约205.5千克氮·公顷）显着提高了粮食产量（平均10359.2千克·公顷）和收获指数（HI，平均0.58）。此外，施氮提高了穗叶的氮浓度，延缓了衰老。与对照相比，最大延迟为 3.4 天。在粮食最高产时，衰老的发生可推迟1.6-1.9天。然而，穗叶衰老延迟对叶片 RemN 对籽粒氮的贡献产生了负面影响，在 205.5 kg N ha 时观察到的最大限值为 16.0。此外，施氮肥还可以降低最大灌浆速率（G）、最大粒重（W）和达到最大灌浆速率的时间（T）。较高的谷物产量及其对氮的响应依赖于衰老开始和 T 之间较短的时间间隔。在施氮量为 196.85 kg N ha（接近最佳施氮量 205.5 kg N ha）时，最小时间间隔可以减少到约 2.4 天，氮肥相对产量响应最大为 39.98%。最佳氮肥通过延迟穗叶衰老的开始并改变其 RemN 来提高谷物产量，从而影响籽粒灌浆。通过考虑穗叶衰老的开始、RemN 与籽粒灌浆的关系，它为在最佳氮肥下实现更高产量提供了宝贵的见解。