Effects of cattle grazing, trampling and excrement deposition on microbial nitrogen transformations in upland soil

Rates of selected soil nitrogen transforming processes as well as kinetic parameters of denitrification enzymes were determined in a cattle overwintering area. Soils from three localities differently impacted by the cattle (severe, moderate, control with no impact) were examined. In cattle-influenced soils, total N, organic C and pH were significantly increased. Consequently rates of potential mineralization, nitrifying enzyme activity and denitrifying enzyme activity (DEA) were enhanced compared to control, while potential nitrogenase activity was lowered in both soils influenced by cattle. The soils differed substantially in DEA, which was about 60 ng N₂O-N g dw^-1 h^-1 in control soil but 3 times and 34 times higher in moderately and severely impacted soils, respectively. The soils also exhibited significantly different maximum reaction velocity (V) and Michaelis-Menten constant (K_m) of enzymes responsible for reduction either of nitrate to nitrous oxide or of nitrous oxide to di-nitrogen. Results suggest that the cattle-induced stress alters the functioning of soil microbial community.