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

Abstract

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.