Upper-bound theoretical carbon mitigation potential of substituting mineral fertilizers with livestock manure nutrients in China: evidence from provincial panel data

Introduction Manure nutrient recycling is an important pathway for reducing mineral fertilizer dependence and improving agricultural nutrient circularity, but its mitigation effect should be distinguished from actual realized emission reduction. This study estimates the upper-bound theoretical carbon-mitigation potential of substituting mineral fertilizer nutrients with livestock and poultry manure-derived nutrients in China. Methods Using provincial panel data for 31 provinces from 2005 to 2024, manure resources and manure-derived N, P 2 O 5 , and K 2 O supplies were quantified, and upper-bound ER was calculated using nutrient-specific fertilizer emission factors. Dagum Gini decomposition, global Moran’s I, and the Spatial Durbin Model were applied to examine regional inequality, spatial clustering, and conditional spatial associations. Results Results show that national upper-bound ER declined from 2.183 × 10 7 t CO 2 -eq in 2005 to 1.677 × 10 7 t CO 2 -eq in 2019, rebounded to 2.021 × 10 7 t CO 2 -eq in 2023, and slightly decreased to 1.962 × 10 7 t CO 2 -eq in 2024. The western region contributed 42.43% of the national total in 2024. Spatial dependence was significantly positive. Manure resource intensity had positive direct and total effects, whereas fertilizer intensity had negative direct and total effects. Agricultural GDP was positively associated with mitigation potential, while mechanization, urbanization, and cropping structure showed heterogeneous local and spillover effects. Robustness and regional analyses confirmed a stable local resource-endowment effect but region-specific spillover patterns. These estimates represent theoretical upper bounds rather than realized mitigation. Discussion China possesses substantial but spatially uneven theoretical carbon-mitigation potential from manure-based mineral fertilizer substitution. Converting this technical upper bound into realized mitigation requires region-specific improvements in manure collection, treatment, transport, nutrient matching, and field application. Policies should therefore shift from maximizing manure return alone toward spatially coordinated, agronomically appropriate, and environmentally controlled nutrient recycling.