Co-Culture of Rice–Chinese Soft-Shell Turtle Increased the Food Yields and Economic Benefit with Less Greenhouse Gas Emissions

Converting conventional rice monoculture to co-culture with fish is a common strategy to increase farmers’ incomes. The Chinese soft-shell turtle is a typical high-value species for paddy co-culture, but the effects of the co-culture system (RT) on greenhouse gas emissions (GHG) are poorly understood. This study evaluated the impacts of RT on economic benefits and greenhouse gas emissions. Our results showed that RT co-culture did not significantly increase rice yield, but it provided additional income from turtle sales, increasing net profits. GHG emission responses to RT differed between the two farms. In farm 1, RT increased CH4 emissions from the rice-cultivated area but decreased them from the turtle culture area, resulting in no net effect on total CH4 emissions. The reduction of CH4 emissions in the turtle culture area was associated with lower DOC content and reduced methanogenic gene mcrA abundance. In farm 2, RT reduced CH4 emissions from both areas, lowering total CH4 emissions by 36.5%, which was linked to less water flooding and higher methanotrophic gene (pmoA) abundance. Total N2O emissions were not significantly affected by RT at either farm. RT increased indirect GHG emissions, but these accounted for only 7.2–16.9% of total emissions. Overall, RT reduced total GHG emissions by 27.7% at farm 2, with no significant change at farm 1. These findings suggest that RT can enhance economic benefit while lessening total GHG emissions.