Spatiotemporal variation of nitrogen indicators related to agricultural green development in China

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.