Sheep grazing stimulated plant available soil nitrate accumulation in a temprate grassland

We investigated the effects of increasing grazing - ntensities on N availability (inorganic N, n-N, for plant and microbial growth, e.g. NO /sub 3/ N, NH /sub 4/+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 NO/sub 3/ N (R /sup 2/ = 0.988, P = 0.006) was well depicted by curvilinear equations. Moreover, soil NO/sub 3/ N, NH/sub 4/ +N and inorganic N varied significantly with sample date, year, and soil water content (SWC, percentage). There were also significant correlation between date and grazing intensities on soil NO/sub 3/ -N, NH/sub 4/ +N and n-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. (author)