SHEEP GRAZING STIMULATED PLANT AVAILABLE SOIL NITRATE ACCUMULATION IN A TEMPERATE GRASSLAND

We investigated the effects of increasing grazing I ntensities on N availability (inorganic N, In-N, for plant and microbial growth, e.g., NO3--N, NH4+-N) and variability in soils of 0-10 cm depth during 2009-2010, within a framework of a long-term grazing study. The results showed that the relationship for grazing intensity with respect to soil NO3--N (R-2 = 0.988, P = 0.006) was well depicted by curvilinear equations. Moreover, soil NO3--N, NH4+-N and inorganic N varied significantly with sample date, year, and soil water content (SWC, %). There were also significant correlation between date and grazing intensities on soil NO3--N, NH4+-N and In-N. SWC and temperature had more impact on soil available N than grazing, especially with respect to the seasonal dynamics of the soil N pool. Grazing intensity, in combination with SWC (precipitation) and temperature, controlled soil N availability and, therefore, affect the N cycles and plant growth within semiarid grasslands.