Biochar drives microbially-mediated rice production by increasing soil carbon.

The effects of an on-site biomass (rice straw) equivalent biochar-returning strategy (RSC) on rice yield, soil nutrients and bacterial community composition were examined in a four-year field trial (2013-2016) conducted in a paddy field in south China. Three treatments were set up including annual on-site biomass return (RS, rice straw at 8 t ha-1 yr-1), annual on-site biomass equivalent biochar-return (RSC, rice straw biochar at 2.8 t ha-1 yr-1 with a 35 % carbonization rate) and control (CK, no rice straw or biochar added). Results showed that a low rate of biochar application (RSC) could significantly increase rice yield in four successive years. The increase in rice yield was mainly attributed to the increase in soil potassium and magnesium contents resulting from the presence of the unique surface functional groups of biochar. As a result of biochar amendment, soil bacterial cooperative relationships were improved in the RSC, compared to those in the RS treatment. Our study indicated that RSC might be promoted as a promising strategy to enhance rice productivity and soil fertility in a sustainable way.