Moreover, total VFA concentrations of treated group were numerical higher than in the control group. The C3 in the treated group was higher (p < 0.05) but C2/C3 was lower when compared with the untreated rice straw, while 50 g/kg urea-treated rice straw, 20 g/kg urea + 20 g/ kg Ca(OH)2-treated rice straw and 30 g/kg urea + 20 g/kg Ca(OH)2-treated rice straw were not different (p > 0.05).