Synchronizing the nitrogen (N) supply of slow- and controlled-release N fertilizers (SCRNFs) with rice N demand is pivotal in substituting multiple urea applications by a single basal application of SCRNFs. Traditional assessment of N supply characteristics focuses mainly on N release patterns, which are only applicable to coated SCRNFs and ignore N transformation mechanisms, thus raising the need for a more universal and reliable index. Based on the ability of crop N status to detect N deficiency or excess, we hypothesized that employing leaf N balance index (NBI) as a measure of N status could provide new insights into assessing N supply characteristics of SCRNFs. We conducted field experiments involving four individual SCRNFs-humic acid urea (HAU), sulfur-coated urea (SCU), urease inhibitor urea (UIU), and polymer-coated urea (PCU)- and their four combined forms, along with the high-yield urea split application as control (CK). The results showed that NBI dynamics relative to CK could reflect the N supply potential of different SCRNFs while classifying them as short-, medium-, and long-acting fertilizers. Combinations that incorporated the long-acting SCRNF (PCU) consistently outperformed others in yield (by 5.5%) and N use efficiency (by 42.8%) by providing a more consistent and efficient N supply throughout the rice growth cycle. Grain yield showed negative correlation with the difference in NBI dynamics between SCRNFs and CK, indicating synchronizing N supply between one-time application of SCRNFs and conventional high-yield fertilization is the key for high yield. Our findings identify the potential of N status diagnosed by leaf NBI to evaluate N supply characteristics of SCRNFs and emphasize the significant role of synchronized N supply for a one-time SCRNF application.

中文翻译：

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优化水稻产量：利用叶片氮平衡指数评价缓控释肥的供氮特性

将缓释控释氮肥 (SCRNF) 的氮 (N) 供应与水稻氮需求同步，对于用 SCRNF 的单次基础施用替代多次尿素施用至关重要。传统的氮供应特性评估主要关注氮的释放模式，仅适用于包覆SCRNF，而忽略了氮的转化机制，因此需要一个更通用、更可靠的指标。基于作物氮状态检测氮缺乏或过量的能力，我们假设采用叶片氮平衡指数（NBI）作为氮状态的衡量标准可以为评估 SCRNF 的氮供应特征提供新的见解。我们进行了现场实验，涉及四种单独的 SCRNF——腐殖酸尿素 (HAU)、硫包衣尿素 (SCU)、脲酶抑制剂尿素 (UIU) 和聚合物包衣尿素 (PCU)——以及它们的四种组合形式，以及高-产量尿素分裂应用作为对照(CK)。结果表明，NBI相对于CK的动态可以反映不同SCRNF的供氮潜力，同时将其分为短效、中效和长效肥料。通过在整个水稻生长周期提供更加一致和高效的氮供应，采用长效 SCRNF (PCU) 的组合在产量（提高 5.5%）和氮利用效率（提高 42.8%）方面始终优于其他组合。籽粒产量与SCRNFs和CK的NBI动态差异呈负相关，表明一次性施用SCRNFs与常规高产施肥之间的同步供氮是高产的关键。我们的研究结果确定了通过叶片 NBI 诊断的氮状态评估 SCRNF 的氮供应特征的潜力，并强调了同步氮供应对于一次性 SCRNF 应用的重要作用。