Deep application of nitrogen fertilizer (DANF) is a strategy based on applying nitrogen fertilizer in the plow layer where it is not exposed to the surface of the soil. Due to its significant beneficial effects on the crop yield and environment, DANF has been applied in many regions throughout the world. However, the effects of DANF on the crop yield, nitrogen apparent recovery (NAR), nitrogen uptake (NU), and farmland management strategies have not been comprehensively evaluated, and thus it is not possible to accurately determine and assess the optimal depth for nitrogen application in widespread use. Therefore, we conducted a meta-analysis based on 716 observations from 96 studies to examine the effects of three nitrogen application depths comprising 5–10 cm, 10–15 cm, and > 15 cm on the crop yield, NAR, and NU. The results showed that compared with the surface application of nitrogen fertilizer, under the three nitrogen application depths of 5–10 cm, 10–15 cm and > 15 cm, the crop yield increased significantly by 7.57%, 11.63%, and 11.85%, respectively, NAR increased by 46.37%, 55.27%, and 58.57%, and NU increased by 19.36%, 26.24%, and 20.93%. In general, a nitrogen application depth of 10–15 cm was most effective. Further analysis showed that the positive effects of DANF on the crop yield, NAR, and NU were influenced by climate factors, soil physical and chemical factors, and management factors. Mean annual precipitation > 800 mm and mean annual temperature > 15 °C were most conducive to improving the crop yield under different nitrogen application depths. In addition, we found that DANF was more effective in fields with poor soil and medium and low fertility. More importantly, DANF was highly adaptable to different crops. When DANF was applied in combination with slow- or controlled- release nitrogen fertilizer, the same or higher yields could be obtained at lower nitrogen application rates, thereby improving NAR and NU. These results provide novel insights into the optimal nitrogen application scheme for global agroecosystems by considering the climatic conditions, soil fertility, nitrogen application method, and nitrogen application rate at specific sites.

深施氮肥 (DANF) 是一种基于在不暴露于土壤表面的犁层施用氮肥的策略。由于其对作物产量和环境的显着有益影响，DANF已在全球许多地区得到应用。然而，DANF对作物产量、氮表观回收率（NAR）、氮素吸收（NU）和农田管理策略的影响尚未得到全面评估，因此无法准确确定和评估氮肥的最佳深度应用广泛。因此，我们基于 96 项研究的 716 项观察结果进行了荟萃分析，以检验三种施氮深度（5-10 厘米、10-15 厘米和 > 15 厘米）对作物产量、NAR 和 NU 的影响。结果表明，与表施氮肥相比，在5~10 cm、10~15 cm和>15 cm 3种施氮深度下，作物产量显着增产7.57%、11.63%和11.85%， NAR分别增长46.37%、55.27%和58.57%，NU增长19.36%、26.24%和20.93%。通常，施氮深度为 10-15 厘米最为有效。进一步分析表明，DANF对作物产量、NAR和NU的正向影响受气候因素、土壤理化因素和管理因素的影响。年均降水量＞800 mm和年均气温＞15℃最有利于不同施氮深度下作物产量的提高。此外，我们发现 DANF 在土壤贫瘠和中低肥力的田地中更有效。更重要的是，DANF 对不同作物具有很强的适应性。当DANF与缓释或控释氮肥配施时，可以在较低的施氮量下获得相同或更高的产量，从而提高NAR和NU。这些结果通过考虑特定地点的气候条件、土壤肥力、施氮方法和施氮量，为全球农业生态系统的最佳施氮方案提供了新的见解。从而改善 NAR 和 NU。这些结果通过考虑特定地点的气候条件、土壤肥力、施氮方法和施氮量，为全球农业生态系统的最佳施氮方案提供了新的见解。从而改善 NAR 和 NU。这些结果通过考虑特定地点的气候条件、土壤肥力、施氮方法和施氮量，为全球农业生态系统的最佳施氮方案提供了新的见解。