Microbial interventions reshape methane yield trade-offs in smallholder rice systems: a randomized controlled trial

Abstract

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.