Assessment of the Effects of Commercial or Locally Engineered Biochars Produced from Different Biomass Sources and Differing in Their Physical and Chemical Properties on Rumen Fermentation and Methane Production In Vitro

SIMPLE SUMMARY: This in vitro study was undertaken to assess the effects of seven biochars (four commercial and three locally engineered) on rumen microbial fermentation and methane production. The biochars were produced via the pyrolysis of different biomass sources and differed in their chemical and physical properties. They were evaluated at 1%, 2%, or 5% of the substrate’s dry matter using batch cultures of ruminal fluid (with 24 h incubation). Despite the contrasting physical and chemical characteristics of the biochars evaluated, neither rumen fermentation (pH, volatile fatty acids, and ammonia-nitrogen) nor methane production were affected. At the examined doses and under the experimental conditions, biochar was ineffective, and it is not a viable option for mitigating enteric methane production. ABSTRACT: In recent years, interest in using biochar as feed additives to mitigate enteric methane (CH(4)) emissions from ruminants has increased. It has been suggested that the mitigating potential of biochar is influenced by its physical (e.g., porosity-related) and chemical (e.g., redox-potential-related) properties. Thus, the aim of this in vitro study was to evaluate the effects of commercial or locally engineered biochars, produced from different biomass sources and differing in their physical and chemical characteristics, on rumen fermentation and CH(4) production. For this purpose, a 24 h batch culture of ruminal fluid incubations was conducted in a complete randomized block design (repeated three times) that included a negative control (no additive), a positive control (monensin, 10 mg/mL), and four commercial and three locally engineered biochars, each evaluated at 1%, 2%, or 5% of the substrate’s (i.e., the total mixed ration) dry matter. The evaluated biochars greatly differ in their chemical (i.e., moisture, ash, pH, redox potential, volatiles, carbon, fixed carbon, hydrogen, and sulfur) and physical (i.e., fine particles < 250 µm, bulk density, true density, porosity, electrical conductivity, specific surface area, and absorbed CO(2)) properties. Despite these differences and compared with the negative control, none of the biochars evaluated (regardless of the inclusion rate) influenced gas and CH(4) production, volatile fatty acid characteristics (total concentration and profile), or ammonia-nitrogen (NH(3)-N) concentrations. As expected, monensin (i.e., the positive control) decreased (p < 0.05) CH(4) production mainly because of a decreased (p < 0.05) acetate-to-propionate ratio. The results of this study reveal that despite the large differences in the physical and chemical properties of the biochars evaluated, their inclusion at different rates in vitro failed to modify rumen fermentation and decrease CH(4) production. Based on these in vitro findings, it was concluded that biochar does not represent a viable strategy for mitigating enteric CH(4) emissions.