Dept. of Ecology and Evolutionary Biology, Corson Hall, Cornell University, Ithaca, NY 14853, USA.
Sci Total Environ. 2018 Sep 1;635:498-511. doi: 10.1016/j.scitotenv.2018.04.027. Epub 2018 Apr 24.
National-level summaries of crop production and nutrient use efficiency, important for international comparisons, only partially elucidate agricultural dynamics within a country. Agricultural production and associated environmental impacts in large countries vary significantly because of regional differences in crops, climate, resource use and production practices. Here, we review patterns of regional crop production, nitrogen use efficiency (NUE), and major inputs of nitrogen to US crops over 1987-2012, based on the Farm Resource Regions developed by the Economic Research Service (USDA-ERS). Across the US, NUE generally decreased over time over the period studied, mainly due to increased use in mineral N fertilizer above crop N requirements. The Heartland region dominates production of major crops and thus tends to drive national patterns, showing linear response of crop production to nitrogen inputs broadly consistent with an earlier analysis of global patterns of country-scale data by Lassaletta et al. (2014). Most other regions show similar responses, but the Eastern Uplands region shows a negative response to nitrogen inputs, and the Southern Seaboard shows no significant relationship. The regional differences appear as two branches in the response of aggregate production to N inputs on a cropland area basis, but not on a total area basis, suggesting that the type of scaling used is critical under changing cropland area. Nitrogen use efficiency (NUE) is positively associated with fertilizer as a percentage of N inputs in four regions, and all regions considered together. NUE is positively associated with crop N fixation in all regions except Northern Great Plains. It is negatively associated with manure (livestock excretion); in the US, manure is still treated largely as a waste to be managed rather than a nutrient resource. This significant regional variation in patterns of crop production and NUE vs N inputs, has implications for environmental quality and food security.
国家层面的作物生产和养分利用效率总结，对于国际比较很重要，但仅部分阐明了一个国家内部的农业动态。由于作物、气候、资源利用和生产实践在区域上的差异，大国内部的农业生产和相关的环境影响有很大的不同。在这里，我们根据经济研究局（美国农业部-ERS）开发的农场资源区，回顾了 1987-2012 年间美国作物的区域作物生产、氮利用效率（NUE）和主要氮投入的模式。在美国，研究期间 NUE 普遍随着时间的推移而降低，主要是由于作物氮需求以上的矿物氮肥料用量增加。心脏地带区域主导着主要作物的生产，因此往往主导着全国的模式，表现出作物生产对氮投入的线性响应，与 Lassaletta 等人（2014 年）对全球国家规模数据模式的早期分析基本一致。大多数其他地区也表现出类似的反应，但东部高地地区对氮投入表现出负响应，而南部沿海地区则没有显著关系。在基于耕地面积的综合生产对 N 投入的响应中，区域差异表现为两个分支，但在基于总面积的响应中则没有，这表明在耕地面积不断变化的情况下，使用的缩放类型至关重要。在四个地区和所有考虑的地区中，氮利用效率（NUE）与肥料作为氮投入的百分比呈正相关。氮利用效率（NUE）与除北部大平原以外所有地区的作物氮固定呈正相关。它与粪肥（牲畜排泄）呈负相关；在美国，粪肥仍然主要被视为需要管理的废物，而不是养分资源。作物生产和 NUE 与 N 投入的模式在这些地区存在显著差异，这对环境质量和粮食安全有影响。
