摘要:氮素在农业和食物系统中的行为关乎资源、环境、食物安全和人体健康等重要问题，是反映农业绿色发展的关键指标。本文选取18个与农业绿色发展密切相关的氮素指标，并按照农业绿色发展程度从高到低分成Ⅰ、Ⅱ、Ⅲ和Ⅳ级，基于统计数据和文献资料，通过食物链养分流动模型（NUFER）定量相关氮素指标，分析其时空变化特征，探讨相关氮素指标的影响因素，为农业绿色发展提供改善意见和建议。结果表明，1980—2017年间全国氮素使用强度、环境排放及整体利用效率均呈现由Ⅰ级向Ⅳ级水平转变的下降趋势，秸秆循环利用效率、大部分氮素生产类以及食物消费类的指标均呈现由Ⅳ级向Ⅰ级水平转变的上升趋势。从空间分布看，氮素投入和环境损失较高的区域主要分布在华北地区、华东地区、华中地区以及华南地区；食物消费水平在各地区均有提升，其中东部地区提升更明显；东部和北部地区的单位植物和动物蛋白产量水平相对较高，但仍处于Ⅲ级水平；效率类指标在31个省份中，大部分地区处于Ⅲ和Ⅳ级水平。与1980年相比，2017年全国氮素指标Ⅳ级和Ⅲ级水平占比变化不大，但Ⅰ级水平占比由27.1%降低至8.3%，农业绿色发展水平整体呈下降趋势。七大地区中各个地区Ⅰ级水平占比均降低，并且大部分地区均低于30.0%，Ⅲ级和Ⅱ级水平的占比明显增加。在指标类型方面，与1980年相比，2017年氮素生产类和食物消费类指标等级在Ⅳ级水平占比降低，农业绿色发展水平呈上升趋势；氮素环境排放类和效率类指标等级在Ⅰ级和Ⅱ级水平占比之和也在降低，农业绿色发展水平呈下降趋势。这是由种植业和畜牧业氮素资源投入高、种植以及养殖结构改变、农牧系统生产脱节严重、社会经济发展不平衡等因素造成的。因此，需要针对不同类型指标的时空变化特征，通过测土配方施肥、改变种养结构和应用氮素减排技术与政策等手段实现氮素指标的优化，推动中国农业绿色发展。
Abstract:Nitrogen is an important indicator of green development of agriculture, which is related to resources, environment, food security and human health in agricultural and food production systems. In this study, the model of NUtrient Flows in food chains, Environmental and Resources use (NUFER) was used to quantify 18 nitrogen indicators related to agricultural green development in China based on collected statistics and data from the scientific literature. Based on the potential values and thresholds reported in the literature, the levels of agricultural green development of each indicator were divided, from high to low, into levels Ⅰ, Ⅱ, Ⅲ and Ⅳ. These were used to evaluate and analyze the variations in the spatiotemporal characteristics of the nitrogen indicators, and to identify the factors influencing the relevant nitrogen indicators, which allowed us to suggest improvements for agricultural green development. From 1980-2017, the nitrogen use intensity indicators, environmental emission indicators and most of the efficiency use indicators decreased from level Ⅰ to level Ⅳ. The straw recycling efficiency indicator, most of the nitrogen production indicators and the food consumption indicators increased over time from level Ⅳ to Ⅰ. From the spatial distribution perspective, nitrogen input and environmental losses increased in the north, east, central, and south regions of China. The diet consumption level increased in all regions and was more pronounced in the eastern regions. Compared with 1980, the unit animal protein production and unit area plant protein production levels in the east and north of China were higher in 2017, but still at level Ⅲ. The levels of the efficiency indicators of agricultural green development in all regions of China were low, and most regions were still at level Ⅲ and Ⅳ in 2017. Compared to 1980, the nationwide proportion of nitrogen indicators at levels Ⅳ and Ⅲ were relatively stable in 2017, and the proportion of indicators at level Ⅰ decreased from 27.1% to 8.3%. From 1980 to 2017, the levels of agricultural green development across the whole China decreased. Among the seven major regions, the proportion of level Ⅰ in each region decreased (with most areas below 30.0%), while the proportion of levels Ⅲ and Ⅱ significantly increased. In terms of indicator types, the proportion of nitrogen production and food consumption indicators at level Ⅳ decreased in 2017 compared with 1980, and the sum of the proportion of nitrogen environmental emissions and efficiency indicators at levels Ⅰ and Ⅱ also decreased. The reasons for these trends include the irrational use of nitrogen resources in crop-livestock systems, changes in planting and breeding structures, inadequate integration of agriculture and livestock husbandry, and uneven development of the economy and society. Therefore, based on the characteristics of the spatiotemporal changes of these different types of indicators, it is necessary to optimize the use of nitrogen to improve the nitrogen indicators by means of soil fertilization, changing the cultivation structure, applying nitrogen emission reduction technologies and policies, and promoting agricultural green development in China.
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