Objective Focusing on the nitrogen (N) and phosphorus (P) nutrient cycle, this paper comprehensively evaluated the current status of the planting and breeding industries, livestock manure carrying capacity, arable land nutrient loadings of N and P from livestock and poultry manure, and associated environmental risks in Zhouqu County. The aim was to systematically explore the optimization paths for planting-breeding balance in this typical ecologically fragile plateau area, provide a theoretical basis for the rational utilization of livestock manure resources, optimizing the layout of the planting and breeding industries, and promoting the development of integrated planting-breeding and ecological circular agriculture.

Method Through data review and field surveys, the resource quantity and distribution characteristics of livestock manure in Zhouqu County were clarified, and the nutrient demands of main crops were estimated. The study analyzed crop nutrient demands and nutrient supply from manure under different application ratios. Different types of livestock were converted into "pig equivalents" (PE), and the land carrying capacity indices (I) based on N and P₂O₅ were calculated for each township. Furthermore, the environmental loading rates and pollution risk levels, expressed as pig equivalents, were analyzed under the existing scale of production.

Results (1) Although livestock manure resources in Zhouqu County are abundant, nutrient distribution is uneven. The effective N and P₂O₅ from manure totaled 713.2 t and 236.8 t, respectively, which could only meet 79.3% and 62.6% of the total nutrient requirements of major crops. This indicates that the manure cannot completely replace chemical fertilizers, necessitating precise supplementary application. (2) In 2023, the actual pig equivalent in Zhouqu County was 1.6×10⁵ heads. Under a 60% manure application ratio, the maximum pig equivalent bearable by N nutrient was 1.4×10⁵ heads, with a land carrying capacity index of approximately 1.1, indicating a slightly overloaded state. Under a 50% manure application ratio, the maximum pig equivalent by P₂O₅ was 1.7×10⁵ heads, with an index (I) of 1.0, achieving a planting-breeding balance. (3) Regarding arable land environmental risks, the situation is generally controllable but remains locally high-risk. The average livestock manure loading rate in Zhouqu County was 22.1 t/hm², with average arable land loadings of Total Nitrogen (TN) and Total Phosphorus (TP) at 54.3 kg/hm² and 8.3 kg/hm², respectively. The arable land risk warning value was 0.7, classifying the risk level as Grade III, posing a threat of environmental pollution.

Conclusion Under the current scale of livestock and poultry farming in Zhongqu County, the overall environmental risk of land for manure assimilation is controllable, though high-risk areas persist locally. Nonetheless, manure alone remains insufficient to meet the nutrient demands of the crop industry. Based on the nitrogen balance, the manure carrying capacity of cropland allows for a manure-to-nutrient application ratio of up to 60%, posing a slight risk of overloading. Given the fragility of the plateau ecosystem, it is recommended to adopt the phosphorus balance as the benchmark (I=1.0) and cap the manure-to-nutrient application ratio at 50%.