Dobermann Achim, Cassman Kenneth G
Department of Agronomy and Horticulture, University of Nebraska-Lincoln, P.O. Box 830915, Lincoln, NE 68583-0915, USA.
Sci China C Life Sci. 2005 Sep;48 Suppl 2:745-58. doi: 10.1007/BF03187115.
At a global scale, cereal yields and fertilizer N consumption have increased in a near-linear fashion during the past 40 years and are highly correlated with one another. However, large differences exist in historical trends of N fertilizer usage and nitrogen use efficiency (NUE) among regions, countries, and crops. The reasons for these differences must be understood to estimate future N fertilizer requirements. Global nitrogen needs will depend on: (i) changes in cropped cereal area and the associated yield increases required to meet increasing cereal demand from population and income growth, and (ii) changes in NUE at the farm level. Our analysis indicates that the anticipated 38% increase in global cereal demand by 2025 can be met by a 30% increase in N use on cereals, provided that the steady decline in cereal harvest area is halted and the yield response to applied N can be increased by 20%. If losses of cereal cropping area continue at the rate of the past 20 years (-0.33% per year) and NUE cannot be increased substantially, a 60% increase in global N use on cereals would be required to meet cereal demand. Interventions to increase NUE and reduce N losses to the environment must be accomplished at the farm-or field-scale through a combination of improved technologies and carefully crafted local policies that contribute to the adoption of improved N management; uniform regional or national directives are unlikely to be effective at both sustaining yield increases and improving NUE. Examples from several countries show that increases in NUE at rates of 1% per year or more can be achieved if adequate investments are made in research and extension. Failure to arrest the decrease in cereal crop area and to improve NUE in the world's most important agricultural systems will likely cause severe damage to environmental services at local, regional, and global scales due to a large increase in reactive N load in the environment.
在全球范围内，过去40年谷物产量和氮肥消费量几乎呈线性增长，且二者高度相关。然而，不同地区、国家和作物在氮肥使用历史趋势和氮素利用效率（NUE）方面存在巨大差异。必须了解这些差异的原因，才能估算未来的氮肥需求。全球氮需求将取决于：（i）种植谷物面积的变化以及为满足人口增长和收入增加带来的谷物需求增长所需的相关产量增长；（ii）农场层面的氮素利用效率变化。我们的分析表明，到2025年全球谷物需求预计增长38%，如果能停止谷物收获面积的持续下降，并将施氮后的产量响应提高20%，那么谷物氮肥使用量增加30%就能满足需求。如果谷物种植面积继续以过去20年的速度（每年-0.33%）减少，且氮素利用效率无法大幅提高，那么要满足谷物需求，全球谷物氮肥使用量就需要增加60%。必须通过改进技术与精心制定的地方政策相结合，在农场或田间层面采取措施提高氮素利用效率并减少氮素向环境中的流失，这些政策有助于采用改进的氮管理方法；统一的区域或国家指令不太可能在维持产量增长和提高氮素利用效率两方面都有效。几个国家的例子表明，如果在研究和推广方面进行充分投资，氮素利用效率每年可提高1%或更多。如果不能阻止世界最重要农业系统中谷物种植面积的减少并提高氮素利用效率，那么环境中活性氮负荷的大幅增加可能会在地方、区域和全球范围内对环境服务造成严重破坏。
