Biochar application increased methane emission, soil carbon storage and net ecosystem carbon budget in a 2-year vegetable–rice rotation

The effect of biochar application on the net ecosystem carbon budget (NECB) and the mechanism controlling methane (CH4) emission in paddy soils under vegetable–rice rotations are poorly understood. A 2-year field experiment was conducted with three treatments: control (no fertilizer or biochar application), chemical fertilizer (BC0) and biochar plus chemical fertilizer application (BC1) to analyze greenhouse gas (GHG) fluxes, soil organic carbon (SOC) content, as well as the abundance and community structure of methanogens and methanotrophs in a vegetable–rice rotation. Biochar addition (BC1) did not affect the yield, or the emission of total CH4 or nitrous oxide (N2O) but significantly increased carbon dioxide (CO2) emission as compared to BC0 in the vegetable season. Rice yield in BC1 was 14.1 % higher than in the control but was lower than in BC0 because of lower available nutrients in BC1 than in BC0. During the rice season, cumulative CH4 emission under BC1 was increased by 2.65 times as compared with BC0 (P