­Title : Enhanced Soil Net N Mineralization and N Cycling of Annual Pasture Under Rotational Grazing in an Arid Region of China

Understanding the effects of rotational grazing on soil nitrogen (N) mineralization and cycling is critical for better management and sustainable development of grassland ecosystems. However, these effects in annual pastures, as well as the underlying mechanisms involved, are unclear. In this study, a two-year field experiment (from May to October) was conducted in annual wheat/rye pasture in the arid region of the Hexi corridor in China to explore how grazing (rotational grazing and non-grazing) affects soil net N mineralization and N cycling. We measured temporal changes in the soil N mineralization rate and inorganic N in annual pasture by taking samples from the upper 0–10 cm of soil and employing an intact soil core in situ incubation technique. We found that the rate of N mineralization and inorganic N were greatest in July and least in August, and that grazing produced a higher temporal N mineralization rate (N min ) and N nitrification rate (N nit ). The temporal mean N mineralization rate increased by 19% in the grazed plots. Also, it was found that soil moisture was significantly positively correlated with N min , and that soil temperature was positively correlated with soil inorganic N. Microbial biomass nitrogen and soil moisture were the main factors influencing the N mineralization rate in this annual system. The results of this study suggest that grazing increases N cycling by increasing herbage N uptake, N mineralization, and nitrate leaching, whilst decreasing soil N 2 O emissions, and highlight the importance of grazing management in the annual pastures of this arid region