Diagnosing spatial decoupling of manure and crop nutrients in China: drivers and multi-objective optimization for sustainable redistribution

China’s uneven farming distribution creates significant mismatches between manure nutrients and crop demands, causing pollution in surplus areas and deficits in agricultural heartlands. This study diagnosed the distribution and drivers of nitrogen (N) and phosphorus (P) nutrient mismatches, and developed a Non-dominated Sorting Genetic Algorithm II (NSGA-II) optimization model for interprovincial manure redistribution, which minimizes transport distance and application-phase greenhouse gas (GHG) emissions while respecting ecological thresholds across China. China shows a regional N/P imbalance, with surpluses in the west and deficits in densely populated and grain-producing regions, dominated by a nitrogen gap. Nutrient surpluses are jointly driven by regional socio-economic development, cropping structure, and manure management efficiency. Strategic redistribution of 0.300 × 10 6 tons of N and 0.047 × 10 6 tons of P to recipient provinces reduced land carrying capacity saturation rates (LCCSRs) of surplus regions to safe levels and decreased the national average LCCSRs by 39.3% for N and 24.1% for P. Simultaneously, the increase in GHG emissions was controlled to within 8.5%. This study offers theoretical and practical optimization tools for sustainable manure management under China’s carbon neutrality, advancing nutrient goals and establishing quantitative bases for regional circular agriculture and ecological sustainability.