Effects of different straw returning modes on greenhouse gas emissions and crop yields in a rice–wheat rotation system

Abstract

Significant efforts have been made to assess the common straw returning modes on crop yields and greenhouse gas (GHG) emissions. However, the effects of a novel straw returning mode, namely ditch-buried straw returning on GHG emissions are still unknown. We conducted a 2-year field experiment, including four wheat straw returning modes (no straw returning (CK), wheat straw returning with rotary tillage (WR), wheat straw returning with plowing (WP), and ditch-buried wheat straw returning (WD)) to evaluate crop yields and GHG emissions under rice–wheat rotation system. Methane (CH4) and nitrous oxide (N2O) fluxes were measured using the static chamber method from the 2013 rice season to 2015 wheat season. The results indicated that wheat straw returning treatments before rice transplantation significantly increased seasonal CH4 emissions during both the rice seasons and wheat seasons, compared to CK. Annual CH4 emission was lower under WD than that under WR and WP. Straw returning significantly increased N2O emission during the first rice season and second wheat season, compared to CK. Annual N2O emission under WD was significantly lower than that under WP, but significantly higher than that under WR and CK. Straw returning increased both rice and wheat yields compared with CK, and WD had significantly higher annual grain yields of both rice and wheat, with an increase of 7.1%. Across the two rotation cycles, annual yield-scaled GWP of CH4 and N2O emissions under WD was 10.8% lower than that of WR. These results indicated that compared with straw returning via rotary tillage or plowing, ditch-buried wheat straw in rice seasons may reduce GHG emissions while sustaining or even increasing crop yields in the rice–wheat rotation system.