Effect of the herbicide butachlor on methane emission and ebullition flux from a direct-seeded flooded rice field

Application of a commercial formulation of the herbicide butachlor (N-butox ymethyl-2-chloro2',6'-diethyl acetanilide) at 1 kg a.i. ha(-1) to an alluvi al soil planted with direct-seeded flooded rice (cv. Annada), significantly inhibited both crop-mediated emission and ebullition fluxes of methane (CH 4). Over a cropping period of 110 days, the crop-mediated cumulative emissi on flux of CH4 was lowered by similar to 20% in butachlor-treated field plo ts compared with that of an untreated control. Concurrently, ebollition flu x of CH4 was also retarded in butachlor-treated field plots by about 81% co mpared with that of control plots. Significant relationships existed betwee n CH4 emission and redox potential (E-h) and Fe2+ content of the flooded so il. Application of butachlor retarded a drop in soil redox potential as wel l as accumulation of Fe2+ in treated field plots. Methanogenic bacterial po pulation, counted at the maturity stage of the crop, was also low in butach lor-treated plots, indicating both direct and indirect inhibitory effects o f butachlor on methanogenic bacterial populations and their activity. Resul ts indicate that butachlor, even at field-application level, can effectivel y abate CH4 emission and ebollition from flooded soils planted to rice whil st maintaining grain yield.