Effects and mechanisms of grazing on key processes of soil nitrogen cycling in grassland: A review

Abstract

Grazing is one of the most important practices for humans to manage grassland ecosystems. The disturbances of feeding, trampling, resting and excreta returning by herbivores will change plant communities and soil nutrient cycling. With the intensification of human activities, the intensity and frequency of grazing were also increased, which would have important impacts on the key processes of soil nitrogen (N) cycling in grassland. Grazing mainly affects the migration and transformation of N in soils by changing soil physical properties, soil N pool size, as well as the composition and structure of soil microbial community. Generally, moderate grazing could enhance soil N mineralization and nitrification, accelerate soil N turnover, and facilitate plant N use. The effects of grazing on denitrification are closely related to the hydrothermal conditions and soil types. Current results on the effects of grazing intensity on various key processes of soil N cycling remain inconsistent, with underlying mechanism being not clear. Based on extensive review of literature, we summarized the research progresses and the underlying mechanisms of the effects of grazing on key processes of soil N cycling. Some deficiencies in current research were pointed out. Possible key topics in the future study were proposed to provide a reference for further understanding the impacts of grazing on soil N cycling in grasslands.