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. Nitrogen and phosphorus fertilization is an effective pathway to increase soil carbon sequestration through microbial necromass accumulation and plant-derived carbon inputs, as shown by a 180-year soil fertilization experiment, 14C labelling, metagenomics and metabolomics.