131 Effects of biochar type and inclusion level on in vitro gas production dynamics

Abstract Biochar has been studied as a soil amendment for the storage of stable carbon in the soil, contributing to carbon capture and mitigation of greenhouse gas emissions. There may be potential for biochar use as a feed additive to reduce enteric methane (CH4) emissions from growing beef cattle, but it may be dependent on several factors, including biomass source, production methodology, biochar particle size, and several others. Thus, our objective was to determine the effects of 3 different biochars and their level of inclusion on in vitro gas production dynamics of bermudagrass (Cynodon dactylon) hay. Biochars included yellow pine wood (W, Waste to Energy Inc., Slocomb, AL), yellow pine wood modified with calcium hydroxide (CW), and dairy cattle manure (M, Ecochar, Heehugowaard, Netherlands). Air-dried bermudagrass hay with or without biochars was incubated for 48 h with fresh rumen inoculum collected from 4 ruminally cannulated steers. Biochars were investigated at 3 inclusion levels (IL; IL.5 = 0.5%, IL1 = 1.0%, and IL2 = 2.0% of DM). Four incubations were performed. Incubations were performed in an unbalanced, incomplete randomized block design as inclusion levels differed among incubations, with IL.5 only included in the first two incubations (Group1) and IL2 only included in the last two incubations (Group2), but IL1 was included in all four incubations, and it was used to scale the IL.5 and IL2 variables linearly. Enumeration of CH4 production was performed for all samples. Statistical analyses were performed using PROC GLIMMIX of SAS version 9.4 (SAS Institute Inc., Cary, NC). Data were evaluated by group, with biochar, IL, and biochar × IL included in the model, and incubation included as a random variable. There were no effects of biochar, IL, or biochar × IL for either group on any of the fermentation dynamics (P ≥ 0.05), including total gas production, fractional rate of gas production, and lag time before initiation of gas production, for either the exponential or log 2-pool functions. Additionally, there were no differences in grams of CH4 production (P ≥ 0.12) for either group. To compare biochars at all IL, relative CH4 production was explored after adjusting values for IL1 and IL2 in the last two incubations based on the difference in CH4 produced at IL1 in the first two incubations. In terms of relative CH4 production, the M biochar produced approximately 16 and 28% less CH4 than W and CW, respectively, at IL1. Our results indicate that M biochar may allow for reduced CH4 production from beef cattle, but several factors, including biomass source, production methodology, and particle size, should be considered to understand the differences better. Ultimately, further research is warranted to evaluate biochar in greater depth as a feed additive for growing beef cattle.