Soil carbon sequestration enhanced by long-term nitrogen and phosphorus fertilization

Soil organic carbon is crucial for climate mitigation and agroecosystem sustainability, yet its depletion is concerning and its response to long-term fertilization remains unclear. Here we leverage the Broadbalk Classical Experiment at Rothamsted (UK), the world’s longest-running continuous winter wheat fertilization trial, along with ¹⁴C labelling, metagenomics and metabolomics to determine how 180 years of nitrogen (N) and phosphorus (P) fertilization impact soil organic carbon dynamics. Compared with no fertilization, long-term P, N and combined NP fertilization increased the soil organic carbon content by 10%, 22% and 28%, respectively. P application alone disproportionately increased microbial respiration (37%) and biomass (20%), limiting stable carbon formation and slightly increasing labile carbon. N application alone increased microbial carbon use and necromass accumulation efficiency, increasing mineral-associated carbon build-up. Combined NP fertilization enhanced plant-derived carbon inputs and the transformation of labile carbon into stable carbon, increasing soil organic carbon quantity and stability. A meta-analysis of the effects of fertilization duration on soil organic carbon revealed that N and P fertilization globally increased cropland soil organic carbon by 21% and 13%, and these promoting effects decreased before increasing after 16 and 34 years, respectively. Overall, long-term mineral fertilization can effectively enhance soil carbon sequestration.