Optimizing methane emissions: Coordinated manure and irrigation practices and their effects on soil carbon dynamics and methanotroph activity

Abstract

Continuous flooding irrigation (CFI) is the conventional practice in rice cultivation but contributes significantly to methane (CH₄) emissions. Alternative wetting and drying irrigation (AWDI) offers improved water efficiency and reduced greenhouse gas (GHG) emissions. Livestock manures like cow manure (CM) are widely used to replenish soil nutrients, yet limited research explores how CM and irrigation practices interact to influence these factors. A greenhouse experiment tested CM at 15 and 30 ton ha⁻¹ under CFI and AWDI. CM application increased CH₄ emissions by up to 62% at higher rates. However, AWDI reduced CH₄ emissions by 32% compared to CFI, with a further 25%–26% reduction when combined with CM. AWDI lowered water usage by 18% without affecting grain yield or biomass, both of which improved under CM. CH₄ emissions under AWDI showed a strong inverse correlation with days after planting, highlighting the role of substrate availability during key growth stages. Extended CM composting further amplified emissions by creating bioavailable compounds favoring methanogens. CFI intensifies CH₄ emissions through sustained anaerobic conditions, while AWDI interrupts methanogenesis via periodic soil aeration. This study underscores the complex interplay between CM, irrigation, and CH₄ emissions, positioning AWDI as a sustainable strategy to reduce GHGs without compromising productivity.