Optimal nitrogen management approach for green transformation of county-level crop-livestock mode: A case study of Tangxian County

The separation of crops and livestock is the main obstacle to environmentally friendly agricultural production. Currently, research on agriculture mainly focuses on large-scale and single objectives, whereas research on multi-objective nutrient optimization management aimed at different environmental characteristics at the county level is relatively lacking. Taking Tangxian County, Hebei Province as an example, this study used the method of multi-objective environmental zoning, collected relevant literature, farmer survey, and statistical data, and then used the NUtrient flow in Food Chain (NUFER) to analyze the current environmental emission characteristics of the crop-livestock mode in Tangxian County and explore the pathways of nitrogen optimization management under the green transformation of the county-level crop-livestock mode. The results showed that: 1) The total nitrogen input was as high as 28.72 Gg, in which the manure and urine resources of livestock and poultry were relatively abundant, reaching 17.55 Gg, but the environmental emissions seriously exceeded the threshold value in Tangxian County. 2) There were significant regional differences in the livestock and poultry manure resources and environmental emissions in Tangxian County, which were mainly concentrated in towns with high numbers of livestock and poultry. Using multi-objective environmental zoning, Tangxian County was divided into low ammonia and high residual overload in the middle, high ammonia and high residual non-overload in the north and east, and high ammonia and high residual overload in the southwest. 3) A three-step nitrogen optimization strategy was implemented in different regions of Tangxian County to achieve environmentally friendly emissions. First, a balanced fertilization method was adopted, which could reduce the number of towns exceeding the threshold of ammonia volatilization, and the residual nitrogen to 45% and 35% respectively. Second, after adding different emission reduction technologies, the number of towns exceeding the threshold values of the two indicators decreased by 30% and 20% respectively. Finally, the ammonia emissions of the whole county can be reduced to the safety threshold by using the optimization of the spatial distribution method, and only 20% of towns with excess residual nitrogen exceeding the threshold remain. The contradiction between agricultural and animal husbandry production and environmental emissions can be solved efficiently and at a low cost through the optimal management of county nitrogen nutrient zoning and the green transformation of the county cultivation mode can be promoted.