Rice cultivation is a major source of agricultural methane emissions, yet many mitigation strategies remain difficult to implement in smallholder systems because of labour, water management, and production constraints. We conducted a large, randomized field experiment in farmer-managed rainfed lowland rice systems to evaluate whether methanotroph-based microbial intervention can reduce methane emissions without compromising rice productivity. We randomly assigned experimental plots to methanotroph treatment, conventional chemical fertilizer, or a no-input control. We repeatedly measured methane emissions throughout the cropping cycle using the closed static chamber method with a portable NDIR methane sensor and recorded rice yield at harvest. Our mixed-effects analysis showed that methanotroph-treated plots consistently produced substantially lower methane emissions than both fertilizer-treated and control plots across all measurement rounds. Methanotroph treatment also substantially reduced methane intensity while maintaining rice yields comparable to those obtained under conventional fertilizer management. Joint analysis of emissions and yield outcomes showed that methanotroph-treated plots clustered toward lower emissions, yield-maintaining conditions relative to alternative management regimes. These findings suggest that methane-related emissions and methane intensity can be substantially reduced while maintaining rice yields under real smallholder management conditions.

Ruminant-derived methane (CH4), a potent greenhouse gas, is a consequence of microbial fermentation in the digestive tract of livestock. Development of mitigation strategies to reduce CH4 emissions from farmed animals is currently the subject of both scientific and environmental interest. Methanogens are the sole producers of ruminant CH4, and therefore CH4 abatement strategies can either target the methanogens themselves or target the other members of the rumen microbial community that produce substrates necessary for methanogenesis. Understanding the relationship that methanogens have with other rumen microbes is crucial when considering CH4 mitigation strategies for ruminant livestock. Genome sequencing of rumen microbes is an important tool to improve our knowledge of the processes that underpin those relationships. Currently, several rumen bacterial and archaeal genome projects are either complete or underway. Genome sequencing is providing information directly applicable to CH4 mitigation strategies based on vaccine and small molecule inhibitor approaches. In addition, genome sequencing is contributing information relevant to other CH4 mitigation strategies. These include the selection and breeding of low CH4-emitting animals through the interpretation of large-scale DNA and RNA sequencing studies and the modification of other microbial groups within the rumen, thereby changing the dynamics of microbial fermentation.