Response of N2O emissions to biochar amendment on a tea field soil in subtropical central China: A three-year field experiment

High inputs of fertilizer nitrogen (N) in tea fields lead to declining soil pH and high emissions of N2O. Amending the soil with biochar can potentially reduce N2O emissions and alleviate soil acidification. To assess the multi-year effects of wheat straw-derived biochar on N2O emissions and tea yield in tea fields, a three-year (2014–2016) field trial following the wheat straw-derived biochar addition was conducted in a tea plantation in southern China under three treatments, namely, conventional treatment (CON, application of conventional organic-chemical fertilizer without biochar), and treatments with conventional organic-chemical fertilizer + straw-derived biochar addition at 10 t ha−1 (BC10) and 40 t ha−1 (BC40) applied once at the beginning of the experiment. Compared to BC10 treatment, the annual total N2O emissions of BC40 were increased by 32.0–46.2% in 2015 and 2016 (p ＜ 0.05) while no significant difference was found between BC10 and CON (p = 0.32–0.97), and N2O emissions of BC10 showed a declined trend during the three years. An increase in tea yield of 24.2–26.0% (p ＜ 0.05) was also observed in BC10 treatment in 2015 and 2016 relative to CON. Differences between treatments in NH4+-N were mostly significant (p ＜ 0.05) but not in NO3--N and DOC (p = 0.16–0.81). The BC40 treatment significantly raised soil pH relative to the CON (p < 0.05). Our collective data indicated that N2O fluxes were positively correlated with the abundance of nirK-denitrification gene during the tea-growing season (p ＜0.05). Long-term impact of straw-derived biochar amendment on N2O was inconsistent with previous short-term biochar studies in tea field soil. Our results indicated that wheat straw-derived biochar amendment at a low rate (BC10) into tea field soil is more feasible for reducing yield-scale N2O emissions in the studied tea field system.