A SEMIEMPIRICAL MODEL OF METHANE EMISSION FROM FLOODED RICE PADDY SOILS

Reliable regional or global estimates of methane emissions from hooded rice paddy soils depend on an examination of methodologies by which t he current high variability in the estimates might be reduced. One pot ential way to do this is the development of predictive models. With an understanding of the processes of methane production, oxidation and e mission, a semi-empirical model, focused on the contributions of rice plants to the processes and also the influence of environmental factor s, was developed to predict methane emission from flooded rice fields. A simplified version of the model was also derived to predict methane emission in a more practical manner. In this study, it was hypothesiz ed that methanogenic substrates are primarily derived from rice plants and added organic matter. Rates of methane production in flooded rice soils are determined by the availability of methanogenic substrates a nd the influence of environmental factors. Rice growth and development control the fraction of methane emitted. The amount of methane transp orted from the soil to the atmosphere is determined by the rates of pr oduction and the emitted fraction. Model validation against observatio ns from single rice growing seasons in Texas, USA demonstrated that th e seasonal variation of methane emission is regulated by rice growth a nd development. A further validation of the model against measurements from irrigated rice paddy soils in various regions of the world, incl uding Italy, China, Indonesia, Philippines and the United States, sugg ests that methane emission can be predicted from rice net productivity , cultivar character, soil texture and temperature, and organic matter amendments.