Methane emission from paddy soils fertilized with cowdung and farmyard manure

Methane emission from rice paddies, which thrive best in waterlogged fields, where the anaerobic condition favours the activities of methanogens in presence of organic matter, is believed to contribute substantially to the increase in the methane content of the atmosphere. Since India is one of the major rice-growing regions of the world, where in some areas farmyard manure prepared from cowdung, rich in methanogens, are used as fertilizers, the methanogenic potential of this age-old practice was studied. The rate of methane emission from inundated rice fields (cv IR-36) was increased appreciably due to cowdung and farmyard manure application, the emission increasing with increasing doses of these fertilizers. The emission was further enhanced when superphosphate and potash were also added. Treatment of sterile soils with non-sterile cowdung and farmyard manure gave higher rates of methane production than when non-sterile soil was treated with sterile cowdung or farmyard manure, indicating that the methanogens present in cowdung and farmyard manure contribute significantly to methane production in soil. As compared to unamended soil farmyard manure increased methane emission through rice plants by about 80% over the entire growth period.