Responses of methane emissions and rice yield to applications of biochar and straw in a paddy field

Directly returning straw back to the paddy field would significantly accelerate methane (CH4) emission, although it may conserve and sustain soil productivity. The application of biochar (biomass-derived charcoal) in soil has been proposed as a sustainable technology to reduce methane (CH4) emission and increase crop yield. We compared the effects of either biochar or rice straw addition with a paddy field on CH4 emission and rice yield. A 2-year field experiment was conducted to investigate a single application of rice straw biochar (SC) and bamboo biochar (BC) (at 22.5 t ha(-1)) in paddy soil on CH4 emission and rice yield as compared with the successive application (6 t ha(-1)) of rice straw (RS). Soil chemical properties and methanogenic and CH4 oxidation activities in response to the amendment of biochar and rice straw were monitored to explain possible mechanism. SC was more efficient in reducing CH4 emission from paddy field than BC. Incorporating SC into paddy field could decrease CH4 emission during the rice growing cycle by 47.30 %-86.43 % compared with direct return of RS. This was well supported by the significant decrease of methanogenic activity in paddy field with SC. In comparison to a non-significant increase with BC or RS application, rice yield was significantly raised with SC amendment by 13.5 % in 2010 and 6.1 % in 2011. An enhancement of available K and P and an improvement in soil properties with SC amendment might be the main contributors to the increased crop yield. These results indicated that conversion of RS into biochar instead of directly returning it to the paddy field would be a promising method to reduce CH4 emission and increase rice yield.