Influence of Azolla on CH4 emission from rice fields

Abstract

Abstract Azolla is an aquatic fern that has been used successfully as a dual crop with wetland rice. Rice fields are a majorsource of atmospheric CH 4 , which is an important greenhouse gas. In this study, field and laboratory experimentsshowed that growing Azolla as a dual crop could enhance CH 4 emission from rice fields. In pot experiments,indications showed that Azolla could mediate CH 4 transport from the floodwater of a rice soil into the atmosphere.It was also found that due to the presence of Azolla, chemical soil properties could be developed, stimulating CH 4 production and decreasing in situ CH 4 removal. Introduction Azolla is a genus of aquatic ferns found floating inswamps, ditches, lakes, and rivers. Because of its aquaticnature, rapid growth, ability to fix N 2 (due to symbiosiswith Anabaena, a blue-green algae), and high N con-tent, Azolla has been used as a green manure or a dualcrop in rice cultivation for many years (Wagner, 1997).It has been shown that incorporation of Azolla as greenmanure is beneficial for rice production both in termsof rice yield and N uptake. Incorporation of Azolla ap-pears to be equivalent to using urea as a source of N(Galal, 1997). Azolla also increases N recovery by thesoil and therefore improves soil fertility in the long term(Kumarasinghe & Eskew, 1993). The use of Azolla as afloating cover in rice fields is also effective in reducingNH