where EF is the methane emission factor (kg CH4/[ha$year]);b0 is the intercept of the regression model; b1 is the regression coefficient of the linear effect of straw incorporation (Straw, t/ha); b2 is the regression coefficient of the quadratic effect of straw incorporation (Straw2, t/ha); b3 is the coefficient for a dummy variable defining the effect of continuous flooding on CH4 emission (Cont.flood; 0= nonflooding irrigated, 1 = continuously flooded); and b4 is the linear effect of straw incorporation in continuous flooding, with respect to the other alternatives. Finally, e is the model error.