Rice straw decomposition in paddy surface water potentially reduces soil methane (CH4) emission

Background: Rice cultivation is a significant methane (CH4) emission source. Rice straw (RS) incorporation into the soil is a key factor that produces higher CH4 emission. The RS waterlogging approach on the soil surface possibly reduces CH4 emission due to not being buried into the soil. However, evaluation of CH4 emission by this approach has not been determined. The objective of this study was to examine CH4 emission under RS waterlogging on surface water compared with RS incorporation into the soil. Methods: We carried out a microcosm experiment in a screen-house with two treatments, including (i) RS incorporation into the soil and (ii) RS waterlogging on the soil surface in triplicates. We compared the CH4 emissions and CH4 accumulation for the rice-growing and off-sowing periods. Yield-scaled CH4 emission was assessed based on total methane emission and rice yield. Results: The results demonstrated that RS waterlogging reduced CH4 emission by 16.9% compared to RS incorporation into the soil. During the rice-growing period, total CH4 emission from RS waterlogging accounted for 36% of the incorporation treatment. However, RS waterlogging is caused by high emissions during the off-sowing stage. The difference between yield-scaled CH4 emissions was insignificant. Conclusions: This study demonstrated that the treatment of RS by waterlogging is an appropriate alternative to conventional RS practices known as incorporation, which increases greenhouse CH4 emission. However, high CH4 emission during the off-sowing period, and RS accumulation in the field are key drivers that possibly contribute to greenhouse gas emissions. Therefore, further evaluation is needed to determine the long-term effects of this approach.