Effect of biochar produced from different biomass sources and at different process temperatures on methane production and ammonia concentrations in vitro

The effects of different biochars on in vitro rumen gas production and fermentation characteristics were investigated using a two (biochar inclusion level, 10 and 100 g biochar/kg substrate) x two (process temperature, 550 or 700 °C) × five (biomass source, Miscanthus straw, oil seed rape straw, rice husk, soft wood pellets or wheat straw) factorial design. The amount of biochar included in incubations had no effect on in vitro fermentation. Overall, inclusion of biochar reduced total gas production to 0.96 (P < 0.001) and methane (CH4) production to 0.95 (P < 0.001) of that in control (no added biochar) incubations. There were no differences in gas or CH4 production between the biomass sources used to produce biochar but total gas (P = 0.058) and CH4 (P = 0.010) production were slightly greater when biochar was produced at 700 rather 550 °C. Addition of biochar to incubations did not change total amounts of volatile fatty acids (VFA) or acetic acid produced during in vitro fermentation; however, the amounts of propionate (0.94; P < 0.001) and butyrate (0.96; P = 0.021) were reduced when biochar was added to incubations. Process temperature had no effect on VFA produced; however, total VFA and the amounts of acetic and butyric acids produced were influenced by biochar biomass source. Ammonia concentrations at the end of incubations were overall 0.84 of control concentrations (P < 0.001)when biochar was added. Both process temperature and biochar biomass source influenced ammonia concentrations which were greater for biochar produced at 700 than 550 °C; concentrations were lowest for biochar produced from Miscanthus straw and greatest for rice husk with oil seed rape straw, soft wood pellets and wheat straw intermediate. Adding biochars with a range of compositions to in vitro assays produced only small reductions in CH4 production. However, the absence of any negative effects of biochar coupled with the observed reduction in ammonia concentrations makes it possible that including biochar in livestock feed could be a practical means of applying biochar to pasture and soil.