Biochar decreases soil N2O emissions in Moso bamboo plantations through decreasing labile N concentrations, N-cycling enzyme activities and nitrification/denitrification rates

Abstract

Biochar application has been shown to be effective in mitigating soil N2O emission in agricultural soils. However, the effect of biochar on soil N2O emission in subtropical plantations and the underlining mechanisms are poorly understood. The objective of this study was to investigate the effect of biochar application rates (0, 5 and 15 t ha−1) on soil properties and N2O emissions within a Moso bamboo (Phyllostachys edulis) plantation in a 24-month field trial. Biochar application significantly (P < 0.05) decreased soil N2O emission, with the reduction rate positively related to the biochar application rate. The reduction in N2O emission by biochar application diminished over time. Biochar did not affect soil temperature (at 5 cm depth), and there were no significant relationships between N2O emission and either soil moisture content or soil microbial biomass C. However, biochar application significantly (P < 0.05) increased the water soluble organic C but decreased soil NH4+-N, NO3−-N and water soluble organic N (WSON) concentrations, soil urease and protease activities, and soil gross nitrification and denitrification rates. Soil N2O flux was positively (P < 0.05) correlated with soil NH4+-N, NO3−-N and WSON concentrations, soil urease and protease activities, and soil gross nitrification and denitrification rates, regardless of the treatment. Structural equation modeling suggests that biochar application decreased soil N2O emissions directly by decreasing soil gross nitrification and denitrification rates, and indirectly by decreasing concentrations of NH4+-N, NO3−-N and WSON, and the activities of urease and protease. We conclude that biochar application decreased soil N2O emission in the Moso bamboo plantation by decreasing labile N concentrations, N-cycling enzyme activities and nitrification/denitrification rates. Our findings suggest that biochar application can be an effective method to mitigate soil N2O emission in subtropical plantations.