VS consumption in the NH3·H2O and H2O2 pretreatments was significantly greater than that of the control, probably because of the progressive hydrolysis of the complex organic matter present in the feeding (Fig. 4). This result was consistent with the finding of Ma et al. (2011), which indicates that the VS content of the rice straw pretreated with NH3·H2O decreased by 28.3% compared with the untreated sample. The highest amount of VS consumed in the NH3·H2O pretreatment was at 4%, followed by 3%, 2%, and 1%. A similar trend was also observed for the H2O2 pretreatment. However, no significant difference was observed between 3% and 4%. The main contents of VS are volatilizable inorganic salts and organic matter, which is the substrate of AD. Thus, VS consumption reflects the utilization of the material (Rowena et al. 2011; Chu et al. 2011). Rafique et al. (2010) showed that VS consumption corresponded directly to the biogas production for the chemical treatment in AD. The current study found similar results in that 4% NH3·H2O and 4% H2O2 exhibited the highest biogas production (Fig. 3), indicating that NH3·H2O and H2O2 pretreatments can improve digestibility and increase the biogas yield of rice stalk significantly.