Response of CH4 emissions to straw and biochar applications in double-rice cropping systems: Insights from observations and modeling.

Paddy soil plays an essential role in contributing to the emission of methane (CH4), a potent greenhouse gas, to the atmosphere. This study aimed to demonstrate the effects of straw incorporation and straw-derived biochar amendment on CH4 emissions from double-rice cropping fields and to explore their potential mechanisms based on in-situ field measurements conducted for a period of three years (2012-2014) and model analysis. The results showed that the improved soil aeration due to biochar amendment resulted in low CH4 emissions and that sufficient substrate carbon availability in straw amendment treatments caused high CH4 emissions. The newly developed CH4 emission module for the water and nitrogen management model (WNMM), a process-based biophysical model, performed well when simulating both daily CH4 fluxes and the annual cumulative CH4 emissions under straw incorporation and biochar amendment. Results of our study indicate that the model has a great potential for upscaling and could benefit mechanism analyses about the factors regulating CH4 emissions. Application of biochar into paddy fields provides a great opportunity to reduce CH4 emissions, and the decrease in CH4 emissions following biochar amendment with repeated crop cycles would sustain for a prolonged period.