A new approach to suppress methane emissions from rice cropping systems using ethephon

Rice is the main staple food for more than half of the world's population. Yet, rice cultivation is subjected to criticism because of its important role in methane (CH₄) emissions. Although several agronomic practices such as controlled irrigation and conservation tillage have been widely adopted to mitigate CH₄ emissions from rice cultivation, the benefits gained by these practices are highly dependent on site-specific soil and climate conditions, and often offset by yield reduction. The use of plant growth regulating compounds having the potential to increase the crop yield and mitigate CH₄ emissions may be an innovative approach to sustainable agriculture. Ethylene (C₂H₄), a plant growth regulator is known to have a strong inhibitory effect on methanogenesis. However, due to gaseous form and low water solubility, C₂H₄ has not been used to suppress methanogenesis in paddy fields. To develop C₂H₄ as a prospective soil amendment for reducing methane (CH₄) emissions, ethephon (2-Chloroethylphosphonic acid), a precursor of C₂H₄ was tested. We found that ethephon reduced CH₄ formation by 43%, similar to other well known methanogenic inhibitors (2-Bromoethanesulfonate, 2-Chlomoethanesulfonate, 2-Mercaptoethanesulfonate). However, ethephon rapidly hydrolyzed to C₂H₄ and methanogenic activity recuperated completely after C₂H₄ removal. To slow down the release of C₂H₄, ethephon was mixed with bio-degradable polymers such as cellulose acetate and applied to paddy soils. We found that compared with the control, the C₂H₄ release of ethephon slowed down to 90 days, and the CH₄ emissions were reduced by 90%. The application of ethephon at lower concentrations did not significantly alter bacterial communities, their relative abundance, and the abundance of methanotrophs, but it significantly reduced archaeal communities and the relative abundance and expression level of methanogens in paddy soils. Results suggest that cellulose acetate-mixed ethephon has great promise to suppress CH₄ emissions in rice paddies while ensuring sustainable yields.