Methane Cycling Microbial Communities in Soil Profile of Pasture Lands Under Different Grazing and Nitrogen Management Scenarios.

Soil methanogenic and methanotrophic microbial communities play a critical role in net methane production from agriculture lands. Their abundance and activity in response to soil conditions and agronomic management must be understood to predict and guide greenhouse gas mitigation efforts. Agronomic management practices can influence the C and N substrate availability to soil microbial communities including the methanogens and methanotrophs. This study was conducted to evaluate the impacts of long-term grazing and nitrogen management practices on net methane production potential in perennial grasslands. The experimental sites are warm season perennial grass pastures under rotations with either annual rye grass or clover in the winter. The clover legume biomass was the only N supplementation for these rotations, whereas other plots with ryegrass received inorganic nitrogen fertilization. Methanogens and methanotrophic abundance in soil profile were estimated in relation to soil health, soil carbon and nitrogen, and microbial biomass. Methanogens were in low abundance compared to other microbial communities, and were mostly present in surface soil. Weak correlations were observed between methanogens and methanotrophs. There were no significant correlations with total microbial biomass or any C and N pools.