Effects of aged biochar additions at different addition ratios on soil greenhouse gas emissions.

Biochar addition is effective in reducing soil greenhouse gas (GHG) emissions, but it's essential to evaluate whether aged biochar retains this capability as its properties change over time. However, research comparing the effects of fresh and aged biochar on soil GHG emissions is limited. Moreover, exploring the priming effect of biochar on native soil organic carbon (SOC) mineralization is crucial for revealing the effect mechanism on soil CO emission. However, research investigating the priming effects of aged biochar is limited. In this study, the effects of aged biochar addition on soil physicochemical properties, GHG emissions, and global warming potential (GWP) were examined through an incubation experiment with three treatments: (1) soil only (CK), (2) 1 % aged maize straw biochar addition (HBC1) and (3) 4 % aged maize straw biochar addition (HBC4), and then their effects were compared with those of fresh biochar from our previous research. C tracer technology was used to assess the priming effect of aged biochar on native SOC mineralization. Results showed that aged biochar improved soil physicochemical properties. Compared to CK, HBC1 and HBC4 reduced CO emissions by 28.02 % and 20.15 %, respectively, and reduced NO emissions by 61.54 % and 66.39 %. HBC4 significantly increased CH emission, whereas HBC1 reduced it. HBC1 and HBC4 reduced GWP by 29.01 % and 21.41 %, respectively. Overall, aged biochar demonstrated a greater reduction effect compared to fresh biochar at the 1 % addition ratio. The CO reduction is attributed to the negative priming effect of aged biochar on native SOC mineralization. The reduction in NO emissions is attributed to aged biochar promoting microbial nitrogen fixation and reducing the ratio of denitrification to nitrification. The variation in CH emissions reflects differing dominant factors influencing CH emission across varying addition ratios. In conclusion, 1 % aged biochar addition demonstrates a more favorable long-term effect on mitigating GHG emissions.