USDA-ARS Cropping Systems and Water Quality Research Unit, USDA/ARS, Columbia, Missouri, United States of America.
Department of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America.
PLoS One. 2022 May 11;17(5):e0267215. doi: 10.1371/journal.pone.0267215. eCollection 2022.
For maize (Zea mays L.), nitrogen (N) fertilizer use is often summarized from field to global scales using average N use efficiency (NUE). But expressing NUE as averages is misleading because grain increase to added N diminishes near optimal yield. Thus, environmental risks increase as economic benefits decrease. Here, we use empirical datasets obtained in North America of maize grain yield response to N fertilizer (n = 189) to create and interpret incremental NUE (iNUE), or the change in NUE with change in N fertilization. We show for those last units of N applied to reach economic optimal N rate (EONR) iNUE for N removed with the grain is only about 6%. Conversely stated, for those last units of N applied over 90% is either lost to the environment during the growing season, remains as inorganic soil N that too may be lost after the growing season, or has been captured within maize stover and roots or soil organic matter pools. Results also showed iNUE decrease averaged 0.63% for medium-textured soils and 0.37% for fine-textured soils, attributable to fine-textured soils being more predisposed to denitrification and/or lower mineralization. Further analysis demonstrated the critical nature growing season water amount and distribution has on iNUE. Conditions with too much rainfall and/or uneven rainfall produced low iNUE. Producers realize this from experience, and it is uncertain weather that largely drives insurance fertilizer additions. Nitrogen fertilization creating low iNUE is environmentally problematic. Our results show that with modest sub-EONR fertilization and minor forgone profit, average NUE improvements of ~10% can be realized. Further, examining iNUE creates unique perspective and ideas for how to improve N fertilizer management tools, educational programs, and public policies and regulations.
对于玉米（Zea mays L.）而言，氮（N）肥的使用通常是在田间到全球范围内通过平均氮利用效率（NUE）来总结的。但是，将 NUE 表示为平均值是具有误导性的，因为在接近最佳产量时，谷物对添加 N 的增加会减少。因此，随着经济效益的降低，环境风险会增加。在这里，我们使用在北美获得的关于玉米籽粒产量对 N 肥响应的经验数据集（n = 189）来创建和解释增量 NUE（iNUE），或 NUE 随 N 施肥的变化而变化。我们表明，对于那些达到经济最佳 N 率（EONR）的最后单位 N，通过谷物去除的 N 的 iNUE 仅约为 6%。换句话说，对于那些在生长季节中损失到环境中的最后单位 N，或者作为无机土壤 N 留在土壤中，这些 N 也可能在生长季节后丢失，或者已经被玉米秸秆和根或土壤有机物质库捕获。结果还表明，对于中等质地的土壤，iNUE 平均降低了 0.63%，对于细质地的土壤，iNUE 降低了 0.37%，这归因于细质地的土壤更容易发生反硝化和/或更低的矿化作用。进一步的分析表明，生长季节水量和分布对 iNUE 的临界性质。降雨量过多和/或降雨不均匀的条件会导致低 iNUE。生产者从经验中认识到这一点，并且天气的不确定性在很大程度上导致了保险肥料的添加。创造低 iNUE 的氮施肥是有环境问题的。我们的结果表明，通过适度的低于 EONR 的施肥和少量的放弃利润，可以实现平均 NUE 提高约 10%。此外，通过检查 iNUE，可以为如何改进 N 肥管理工具、教育计划以及公共政策和法规提供独特的视角和想法。
