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.