Evaluation of the resource utilization potential and land carrying capacity of manure and urine of livestock and poultry in China

This study systematically evaluated the resource utilization potential of manure and urine of livestock and poultry and regional disparities in land carrying capacity across China by developing comprehensive inventories of manure, urine, nitrogen (N), and phosphorus (P) production from eleven major animal categories (including swine, dairy cattle, beef cattle, sheep, goat, layer, broiler, and other species) for 2022. The present research established a sophisticated dual-dimensional assessment framework that integrated nutrient supply-demand balance analysis with cropland load warning systems, implementing an evaluation methodology based on the Nitrogen and Phosphorus Supply-Demand Ratio (NPSDR) to quantify the relationship between manure-derived nutrients and crop requirements. This methodological approach incorporated detailed statistical analysis of regional crop patterns, soil characteristics, and climate conditions to ensure accurate assessment of nutrient utilization capacity. Focusing on six dominant livestock species (swine, dairy cattle, beef cattle, sheep, laying hen, and broiler) that represent the most significant contributors to agricultural nutrient flows, we conducted comprehensive cropland carrying capacity assessment using the standardized Pig Manure Equivalent (PME) conversion methodology to normalize nutrient contents across different manure types, with conversion coefficients derived from extensive laboratory analysis of nutrient composition in various manure types. Results demonstrated national production volumes of 1.625 billion tons for manure and urine, 9.54 million tons for N, and 2.02 million tons for P, with five provinces—Inner Mongolia, Sichuan, Yunnan, Shandong, and Xinjiang—collectively contributing 33.77% of total manure and urine, indicating highly concentrated spatial distribution patterns that reflect regional specialization in animal production. Metropolitan areas including Beijing and Shanghai showed the lowest manure generation quantities with extreme differences exceeding 80-fold compared to high-production regions, exhibiting NPSDR values of only 0.34 and 0.31 respectively and cropland N loads below 100 kg ha⁻¹, significantly lower than the national average of 206 kg ha⁻¹, characterizing a distinct "low-emission, low-demand" resource utilization pattern typical of highly urbanized regions with limited agricultural activity. While national average NPSDR values for N and P were 0.53 and 0.54 respectively, indicating approximately 46.39% remaining theoretical carrying capacity, substantial regional heterogeneity was observed across different agro-ecological zones, with the Qinghai-Tibet Plateau (Qinghai and Tibet) showing extreme N supply-demand ratio of 18.85 in Tibet due to substantial yak and Tibetan sheep inventories combined with high-altitude environmental constraints and extensive grazing systems, resulting in PME load per unit cropland reaching Level VI warning, the highest alert category indicating severe environmental risk, whereas intensive livestock production zones along the southeastern coastal region containing 7.30% of national swine inventory demonstrated excessive N loading rates surpassing 400 kg ha⁻¹ due to severely limited per capita cropland availability (<0.02 hm²), exceeding European Union critical thresholds and triggering Level V warnings, highlighting the critical challenge of nutrient management in high-density livestock production areas. The present research represented the first comprehensive effort to develop synchronized parameters for nutrient estimation across multiple animal categories while enabling precise cropland load assessment, proposing spatially differentiated management strategies through an integrated framework of comprehensive national accounting, prioritized focus on key livestock sources, and regionally adapted governance mechanisms to support sustainable agricultural planning and effective pollution control throughout China, providing valuable insights for policy formulation and implementation of sustainable livestock production systems in developing countries facing similar challenges of agricultural nutrient management and environmental protection.