Combining nitrate with biochar to reduce methanogenesis in vitro

Enteric fermentation significantly contributes to climate change through the release of CH 4 , which also represents a metabolizable energy loss for the animal. Biochar used in the study is produced from gasification of wood waste and contains redox-active elements; therefore, we hypothesized biochar would inhibit CH 4 production. In preliminary studies, biochar retained up to 70% of dosed NO 3 - from passing through a filter. Thus, dosed NO 3 - was hypothesized to interact and accentuate biochar's inhibition of CH 4 production in vitro. A randomized complete block design was used with 200-mL flasks of buffered, anaerobic rumen fluid incubated for 24 h at 39°C in 3 random incubation blocks with 10 duplicated treatment flasks per block that were assessed by orthogonal comparisons using a mixed model. Diets were low and high forage both without or with biochar (5.14% of DM) and without or with NO 3 - (3.85% of DM); additional low forage contained almond hulls (16% of DM) as a forage substitute without or with biochar. Gas production was measured using Mylar balloons, and CH 4 was analyzed using a sensor. Main effects of biochar and NO 3 - in the high forage diet reduced CH 4 production by 84 and 70%, respectively. The ratio of CH 4 to neutral detergent fiber degradability decreased for the main effect of biochar administered with the high forage diet. The combination of biochar and NO 3 - did not surpass any of the individual treatments in lowering CH 4 concentration. Adding almond hulls did not affect CH 4 production. Neutral detergent fiber degradability and acetate:propionate were decreased by NO 3 - . Main effect of almond hulls increased acetate, butyrate, and propionate but lowered higher chain molar percentage of volatile fatty acids. Interactions of biochar and NO 3 - for ammonium- N concentration in both diets support the hypothesis of a biochar matrix mediating NO 3 - reduction as an H 2 sink that is alternate to CH 4 , and minimal residual NO 3 - and NO 2 - suggest complete reduction by 24 h. Microbial N production did not differ among treatments. Although biochar and NO 3 - did not interact for most measurements, further study with longer microbial adaptation is needed to explore potential positive interactions with lower dosages.