This study aimed to evaluate the effects of biochar produced from tropical biomass resources (rice straw, corncob, and bamboo) at different processing temperatures (300, 500, and 700 degrees C) on in vitro rumen fermentation and methane production. Treatments were arranged as a 3 x 3 factorial design with three biomass resources and three biochar processing temperatures. Added biochar occupied 3% of the substrate (DM basic). Two hundred fifty milligrams of the air-dried substrate was incubated in 120 ml bottles, which contained 25 ml of mixed rumen fluid and buffer mineral solution. Total gas and methane production, in vitro digestibility of DM and OM, and in vitro rumen fermentation characteristics were determined at three time points of 4, 24, and 48 h of the incubation. The results showed that biomass resources and processing temperatures affected gas production at 4, 24, and 48 h after incubation (P < 0.01). Interactions between biomass resources and processing temperatures affected gas production at 4 h (P = 0.06) and 24 h (P = 0.001). Biomass resources and processing temperatures affected methane production at different time points of the incubation (P < 0.05), except the effect of biomass resources at 24 h (P = 0.406). Increased processing temperature from 300 to 700 degrees C reduced gas and methane production (P < 0.05). Biomass resources affected OM digestibility after 4 and 24 h of incubation. Processing temperatures and their interaction with biomass resources affected OM digestibility after 48 h of incubation (P < 0.001). NH3-N concentrations at 24 and 48 h were highest for corncob, then rice straw, and lowest for biochar derived from bamboo tree (P < 0.05). Increased processing temperatures resulted in higher NH3-N concentrations at 24 and 48 h of incubation (P < 0.05). To mitigate methane production, biomass resources and processing temperatures should be considered when using biochar as a feed additive in ruminant diets.
