Raised Seedbed Cultivation with Annual Rice–Spring Crop Utilization Enhances Crop Yields and Reshapes Methane Functional Microbiome Assembly and Interaction Networks

Tillage and crop rotation alter soil environments, thereby influencing both crop yields and methane-cycling microbiomes, yet their combined effects on microbial diversity, assembly, and interaction networks remain unclear. Using a two-factor field experiment, we assessed the impacts of raised seedbed vs. flat cultivation and rice–oilseed rape vs. rice–faba bean rotations on crop productivity and the ecology of methanogen (mcrA) and methanotroph (pmoA) communities. Raised seedbed cultivation significantly increased yields: rice yields were 7.6–9.6% higher in 2020 and 4.7–5.8% higher in 2021 than under flat cultivation (p < 0.05). Faba bean and oilseed rape yields were also improved. Flat rice–bean plots developed more reduced conditions and higher organic matter, with a higher NCM goodness-of-fit for methanogens (R2 = 0.466), indicating patterns more consistent with neutral (stochastic) assembly, whereas the lower fit for methanotrophs (R2 = 0.269) suggests weaker neutrality and stronger environmental filtering, accompanied by reduced richness and network complexity. In contrast, raised seedbed rice–oilseed rape plots improved redox potential and nutrient availability, sustaining both mcrA and pmoA diversity and fostering synergistic interactions, thereby enhancing community stability and indicating a potential for methane-cycle regulation. Overall, raised seedbed cultivation combined with legume rotation offers yield benefits and ecological advantages, providing a sustainable pathway for paddy management with potentially lower greenhouse gas risks.