Optimizing the trench area proportion in rice crayfish co-culture systems balances greenhouse gas mitigation and productivity

The rice-crayfish co-culture system (RCS) has emerged as a cornerstone of China's aquaculture sector, yet its greenhouse gas (GHG) emission profile remains contested. While the co-cropping field zone (RCS-Field) demonstrates considerable mitigation potential, the continuously flooded crayfish-trench zone (RCS-Trench) releases substantial methane that can offset the benefits from the field. To address this challenge, we integrated multi-source field data from rice monoculture (RM) and RCS systems across the Middle-Lower Yangtze Plain and calibrated the Denitrification-Decomposition (DNDC) model to simulate system-level GHG emissions. Using recalculated cumulative CH₄ and N₂O emissions as well as the rice yield, we developed a multi-objective optimization framework for determining the trench area proportions. Results showed that CH₄ emissions from RCS-Trench were more than threefold higher than those from RCS-Field, whereas RCS-Field emissions were significantly lower than RM. By contrast, N₂O emissions were lowest in RCS-Trench, falling below both RM and RCS-Field. The global warming potential (GWP) was highest in RCS, followed by RCS-Trench and RM, and lowest in RCS-Field. When integrating rice yield, crayfish production, and GWP, the optimal crayfish-trench proportion was identified as 7.5%-9.0%. These findings provide the first quantitative evidence that regulating trench area can simultaneously mitigate methane emissions, safeguard grain security, and enhance economic returns, thereby offering scientific support for sustainable rice-aquatic co-culture development and contributing to China's "Dual Carbon" strategy.