Responses of soil greenhouse gas emissions to different application rates of biochar in a subtropical Chinese chestnut plantation.

• Biochar reduced soil N 2 O emissions and enhanced CH 4 uptake in a chestnut plantation. • Biochar altered key soil environmental factors important for GHG emissions. • Biochar altered the relationships between soil GHG emissions and labile organic C. • Soil temperature and water-soluble organic C were major controls on GHG emissions. Biochar application has been proposed as an effective measure to mitigate greenhouse gas (GHG) emissions from soil. However, the effects of different biochar application rates on soil GHG emissions and their linkages with biochar-induced changes in soil environmental factors remain unclear in managed plantations. This study examined the responses of soil GHG emissions to different application rates of bamboo leaf biochar in a Chinese chestnut plantation. A two-year field trial was conducted to determine the changes in soil GHG emissions and key soil properties over time in B0 (control), B2, B5 and B10 treatments, representing biochar application rates of 0, 2, 5 and 10 t ha−1, respectively. Biochar application significantly (P < 0.05) decreased soil N 2 O emissions (from 2.60 to 2.11 t ha−1 yr−1) and increased soil CH 4 uptake (from 3.13 to 4.22 t ha−1 yr−1), but did not change soil CO 2 emissions. The biochar inhibition effect on soil GHG emissions increased with increasing biochar application rates, with greater inhibition in the first year than in the second year. Biochar application also decreased the concentrations of soil NH 4 +-N, NO 3 –-N and water-soluble organic N (WSON), but increased the concentrations of water-soluble organic C (WSOC) and microbial biomass C (MBC). Regardless of the treatments, the soil GHG emissions were significantly (P < 0.01) correlated with soil temperature, but not with soil moisture content. Soil CO 2 and N 2 O emissions, and soil CH 4 uptake were positively (P < 0.05) correlated with WSOC concentration under the B0, B2 and B5 treatments only. A significant relationship (P < 0.05) was observed between soil MBC and soil CO 2 emissions (only for the B0 and B2 treatments), and soil MBC and soil N 2 O emissions (only for the B0, B2 and B10 treatments). The results suggest that biochar application rates can alter the relationships between GHG emissions and soil WSOC and MBC concentrations. The soil N 2 O emissions were positively (P < 0.05) correlated with the NH 4 +-N, NO 3 −-N and WSON concentrations in all treatments. This study demonstrated that the management practice (i.e. biochar application to soil) decreased soil GHG emissions in a Chinese chestnut plantation via changes in key soil properties, with implications for the mitigation of soil GHG emissions in subtropical plantations. [ABSTRACT FROM AUTHOR]