LAUSR

Previously, most carbon (C) sequestration research focused on the effects of nitrogen (N) fertilization on soil organic C sequestration rather than on the separate effects of synthetic phosphorus (P) and potassium (K) and the integrated effect of NPK. In this study, a meta-analysis was conducted to synthesize 84 long-term trials with 385 paired comparisons to quantify the variance of soil C storage in response to synthetic fertilizer addition. Compared with unfertilized soil, higher C storage was observed in soils fertilized with NPK, N, P, and K (10, 5, 5, and 2%, respectively) at a depth of 0–20 cm, and changes in soil C storage were dependent on the cropping system, experimental duration, geographic region, and fertilization rate. Soils fertilized with NPK and N in wheat (Triticum aestivum) and maize (Zea mays) cropping systems in the northern region of China had greater soil C storage. The greatest increase in C storage occurred in soils fertilized with P in rice (Oryza sativa) and wheat cropping systems. Additionally, the ratio of N/P added as fertilizer was negatively related to soil C storage. When N, P, and K were applied together, N and P fertilizers explained 49 and 11% of the variability in soil C storage, while the contribution of K was unclear. This study reveals the important roles of P and N fertilizers in soil C sequestration. We estimated that fertilizer use resulted in the sequestration of 947.2–1093 Tg C in China’s croplands from 1980 to 2014.