Nitrogen input alleviates the priming effect of biochar addition on soil organic carbon decomposition

The combination of biochar and nitrogen (N) addition has been proposed as a potential strategy to mitigate climate change by sequestering carbon (C), while simultaneously boosting crop yields. However, our current knowledge about how biochar and N addition alter mineralization of native soil organic C, which is referred to priming effects (PEs), is largely limited. To address these uncertainties, three C₃ biochar (pyrolyzing rice straw at 300, 550, and 800 ℃) and its combination with N fertilizer (urea) were incubated in a C₄-derived soils at 25 ℃ in the laboratory. Our results showed that all these 3 types of biochar with different addition rate caused positive priming of native soil organic C decomposition (up to +58.4%), but negative or no priming occurred in biochar bound N treatments. The maximum negative PEs (-14.5%) were observed in 300 ℃ biochar with 1% addition rate bound N (B₁300N) treatment. We find a negative correlation between the priming intensity and soil inorganic N content across all treatments. Furthermore, the biochar-induced PEs regulated by microbial biomass, fungi/bacteria ratio, and microbial metabolic efficiency. These findings indicated that eligible biochar used for blending traditional mineral fertilizer has a larger climate-change mitigation potential than biochar and fertilizer alone, while sustain relatively high crop yields.