Assessment of the straw and biochar application on greenhouse gas emissions and yield in paddy fields under intermittent and controlled irrigation patterns

Water-saving irrigation and straw and biochar application are common agronomic practices in rice production, and their profound impact on greenhouse gas (GHG) emissions from paddy soils cannot be ignored. A three-year field experiment was conducted in typical paddy fields in the subtropical region of eastern China. The methane (CH4) and nitrous oxide (N2O) emissions with straw or biochar application under intermittent irrigation (II) and controlled irrigation (CI) patterns were systematically assessed, and relevant soil physicochemical properties were measured to clarify the internal linking mechanisms. Five treatments were established: conventional flooding as the control group (CG), intermittent irrigation + straw (II + S), intermittent irrigation + biochar (II + B), controlled irrigation + straw (CI + S), and controlled irrigation + biochar (CI + B). The cumulative CH4 emissions with II + S, II + B, CI + S, and CI + B were reduced by 11.2%, 33.2%, 14.1%, and 40.3%, respectively; while the cumulative N2O emissions increased by 20.2%, 5.8%, 13.6%, and 1.2%, respectively (three-year average). Each treatment significantly reduced the global warming potential (GWP) by 10.1–44.8%, and increased rice grain yield by 7.9–13.3%, significantly reducing the greenhouse gas emission intensity (GHGI) by 16.7–46.7%. With II and CI, straw or biochar application increased the soil pH, ground temperature at 5 cm depth, and soil nitrogen levels and regulated the SOM and DOC contents, which may be closely related to greenhouse gas emission regulation and improvements to soil fertility. Notably, the decrease in the soil mcrA/pmoA gene abundance ratio was a dominant factor in CH4 reduction. Overall, each treatment has the potential to reduce GHG emissions and increase crop productivity in paddy fields, and CI + B achieved the best results. These practices facilitate the development of optimal management strategies for rice cultivation.