Assessment of the influence of biochar on rumen and silage fermentation: A laboratory-scale experiment

The addition of biochar – charcoal produced from pyrolysis of carbonaceous materials – to soil presents several challenges, mainly associated with its low bulk density, dustiness and the risk of loss when applied to hill pastures. Livestock could be an adequate vehicle for biochar delivery to New Zealand pastoral soils via dung pats; however, the potential effects of biochar on rumen metabolism need to be investigated. The objective of this study was to investigate the effect of biochar addition to grass before ensiling on the fermentation process and to test whether the addition of grass silage prepared with biochar or biochar directly to hay affected the in vitro rumen fermentation. The study included the use of different types of starting material (corn stover and pine wood chips), two pyrolysis temperatures (350 and 550°C), post-treatment (addition of different types of bio-oil at a ratio of 0.050mL/g), and different doses of biochar. The use of biochar from either corn stover or pine pyrolysed at 550°C as silage ingredients at doses from 21 to 186g biochar/kg dry matter had no negative effect on the final properties of the silage, and particularly on pH, NH4+-N/total N, and acetic, N-butyric and l-lactic acid concentrations. The same silage mixtures with 84 and 186g biochar/kg dry matter were in vitro incubated with buffered rumen fluid. There was a build-up in total volatile fatty acids (VFA) production (P<0.05) in the presence of biochar – increasing at high doses – irrespective of the type of starting material considered. This increase in VFA was also observed when biochar were added to hay before in vitro incubation, and was enhanced with low-temperature biochar. None of the mixtures of biochar and hay had any significant effect on methane emissions and ammonia released. There was no effect of starting material type or post-treatment on the in vitro incubations. The results obtained in this research demonstrate the lack of negative effect of biochar mixed with grass silage, or hay, on rumen chemistry during in vitro incubations. If large-scale studies including in vivo feeding of cattle with biochar confirm these findings, the use of cattle as a delivery system could become a novel solution to safely apply biochar to New Zealand pastoral soils.