Nitrogen agronomic efficiency (NAE) is crucial for global food security due to its important role in determining crop yields. However, we do not know whether NAE under nitrogen (N) application changes in the long term, and what controls these temporal dynamics. These knowledge gaps could result in high uncertainty in predicting the increase in global crop yields due to N fertilization in the future, threatening global food security. Here, we synthesized 477 N application studies with duration ≥ 5 years in croplands around the globe. Mean long term NAE was 20.8 kg kg, and N application rate, crop type, and N fertilizer type were the most important factors affecting NAE. Overall, NAE did not significantly change in the long term at the global scale. However, a third of studies showed evidence of a consistent directional change in NAE over time (increase: 21 %, decrease: 12 %). Mean annual precipitation (MAP) mostly explained the variation in the temporal trend of NAE. More specifically, NAE tended to decrease over time with the increasing of MAP. To achieve a high and sustained NAE, N should be applied as NHNO or NH form along with both phosphorus and potassium fertilizers. Our meta-analysis study indicates that, although no significant temporal trend of NAE was found at the global scale, we may still over- or underestimate crop yields under certain types of management, resulting in global food insecurity in the future.

中文翻译：

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从长远来看，施氮肥下的氮农艺效率不会随时间而变化：来自 477 项全球研究的证据


氮肥农艺效率（NAE）对于全球粮食安全至关重要，因为它在决定作物产量方面发挥着重要作用。然而，我们不知道施氮 (N) 下的 NAE 是否会发生长期变化，以及是什么控制着这些时间动态。这些知识差距可能会导致预测未来因施氮肥导致的全球作物产量增加的高度不确定性，从而威胁全球粮食安全。在这里，我们综合了 477 项在全球农田中持续时间≥ 5 年的氮应用研究。平均长期NAE为20.8 kg·kg，施氮量、作物类型和氮肥类型是影响NAE的最重要因素。总体而言，从长期来看，NAE 在全球范围内并没有发生显着变化。然而，三分之一的研究表明，NAE 随着时间的推移出现一致的方向变化（增加：21%，减少：12%）。年平均降水量（MAP）主要解释了 NAE 时间趋势的变化。更具体地说，随着 MAP 的增加，NAE 往往会随着时间的推移而减少。为了实现高且持续的 NAE，氮肥应以 NHNO 或 NH 形式与磷肥和钾肥一起施用。我们的荟萃分析研究表明，尽管在全球范围内没有发现NAE的显着时间趋势，但我们仍然可能高估或低估某些管理类型下的作物产量，从而导致未来全球粮食不安全。