Mitigation of Greenhouse Gas Emissions Through Straw Management and Oxygenated and Biochar-Based Fertilizers

Straw returning is a common agricultural practice that can enhance rice (Oryza sativa L.) yield in paddy systems. However, it also leads to a significant increase in greenhouse gas emissions (GHG). Fortunately, this negative impact can be mitigated by implementing enhanced oxygenation strategies during rice cultivation. This study explored the effects of various oxygenation measures on GHG under straw-returning conditions through controlled pot experiments. Six distinct treatments were applied. These included straw not returned (NR, no straw applied), straw returned (SR), controlled irrigation (CI), oxygenation irrigation (OI), application of oxygenated fertilizer (OF, CaO₂), and use of biochar-based fertilizer (CF). All treatment groups, with the exception of the NR group, involved the return of straw to the field. Creating rice production methods that increase yield and decrease emissions is of great importance to agricultural ecology. We postulated that using aeration methods under straw return conditions would stabilize rice yield and reduce GHG. The experimental results were consistent with our hypothesis. The experiment evaluated multiple parameters, including rice yield, leaf photosynthetic performance, soil ammonium and nitrate nitrogen (N) levels, and greenhouse gas emissions. The findings revealed that different oxygenation approaches significantly promoted rice tillering. Oxygenation measures have been shown to enhance rice yield by 19% to 65%. The highest tiller numbers were observed in the SR (22.75) and CF (21.6) treatments. Among all treatments, the CF achieved the highest seed setting rate at 0.94, which was notably greater than that of the other treatments. Total plant biomass was also significantly higher in the straw returning treatment (109.36 g), surpassing all other treatments. In terms of soil nitrogen dynamics, the OF treatment resulted in the highest nitrate nitrogen content. Meanwhile, the ammonium nitrogen concentrations across the four oxygenation treatments (CI, OI, OF, CF) ranged from approximately 7 to 8.9 mg kg^-1. Regarding GHG, the CF treatment exhibited the lowest methane emissions, which were 33% lower compared to the straw returning treatment. The OF led to a 22% reduction in carbon dioxide emissions (CO₂) relative to straw returning. Most notably, the CF reduced nitrous oxide emissions by 37% compared to the straw returning treatment. Overall, SR was found to substantially increase GHG. In contrast, all tested oxygenation measures-CI, OI, OF, and CF-were effective in suppressing GHG to varying degrees. Among these, the CF and OF demonstrated the most balanced and outstanding effects, both in reducing emissions and maintaining stable rice yields.