Alteration of the soil microbiome and enzyme activities by forage-applied manure from cattle fed the methane inhibitor 3-nitrooxypropanol supplement

The microbial fermentation of plant feed by ruminants produces enteric methane (CH4), a potent greenhouse gas. Supplementing ruminant diets with an experimental methane inhibitor, 3-nitrooxypropanol (3-NOP), has been shown to decrease enteric CH4 production, but the effect of manure from these cattle on the soil microbiome has not been studied. In 2017 and 2018, we examined the effects of stockpiled manure and composted manure from cattle fed 3-NOP supplement alone or in combination with monensin (an ionophore) on soil permanganate-oxidizable C, microbial biomass C (MBC), the composition and diversity of prokaryotic and fungal communities, and the activities of β-glucosidase (C cycling), N-acetyl-β-glucosaminidase (C and N cycling), acid and alkaline phosphomonoesterases (P cycling), and arylsuphatase (S cycling) in a forage cropping system. Stockpiled or composted manure from cattle fed 3-NOP increased MBC in 2017, fungal α-diversity in 2018 and the relative abundance of Actinobacteriota, but it decreased the relative abundances of Acidobacteriota and Basidiomycota, relative to stockpiled or composted manure from cattle that were not fed 3-NOP. In 2017, relative to the conventional stockpiled manure, 3-NOP in stockpiled manure increased the activities of N-acetyl-β-glucosaminidase and acid phosphomonoesterase, but these effects were not observed for composted manure. Monensin, when used in combination with 3-NOP, did not affect any of the soil parameters measured in this study. The core microbiome found in 90 % of the soil samples included the bacterial and fungal genera Vicinamibacteraceae and Solicoccozyma, respectively. Therefore, 3-NOP manure or compost altered the composition of the soil microbiome, and the 3-NOP in stockpiled manure increased the potential activities of enzymes involved in C-and-N and P cycling in the first year of the study, and fungal α-diversity in the second year, but no negative or persistent effects of 3-NOP on enzyme activities were observed.