How sustainable agricultural management practices mitigate greenhouse gas emissions in paddy fields.

Agriculture is a major emitter of greenhouse gases (GHG), requiring mitigation through optimized sustainable practices. Although sustainable management practices show promise, especially for significant sources, such as rice paddies, their comparative effectiveness remains unclear due to a lack of multi-treatment experiments conducted under consistent conditions. To address this issue, we conducted a large-scale field study over four growing seasons (i.e. two years) in two rice paddies approximately 500 m apart. The study evaluated the impact of five management practices, halting fertilization, no pesticides, no-tillage, mycorrhizal inoculations, and alternative cultivars, on N2O, CO2, and CH4 emissions. We monitored twenty parallel bifactorial experiments, comprising a total of 640 field plots, and collected data on gas emissions exceeding 23,000 records. Our analysis focused on both fitted coefficients (slopes) and effect sizes across the 40 experiments. Mycorrhizal inoculation decreased equivalent CO2 emissions by 667 mg m-2 h-1, while halting pesticide use increased them by 779 mg m-2 h-1. None of the other four sustainable agricultural practices reduced equivalent CO2 emissions. Halting fertilization showed the greatest reduction in N2O emissions (F=8.07, P<0.001), though this effect diminished over time. Variations in emission types were observed, assessed through the CH4:CO2 ratio, with no-tillage yielding the highest and mycorrhizal inoculum additions the lowest ratios (F=3.1, P=0.02). Our findings highlight the context-dependent nature of sustainable management practices' effects on greenhouse gas emissions, emphasizing the importance of AMF in mitigating climate change and the need for in situ greenhouse-gas-emission measurements when assessing agricultural management strategies.