Effects of grazing exclusion length on soil organic nitrogen in Seriphidium transiliense desert

To explore the effects of different grazing exclusion lengths on soil organic nitrogen, we studied total soil nitrogen, particulate organic nitrogen, light fraction organic nitrogen, soil microbial biomass nitrogen and their distribution ratios in a moderately degraded Seriphidium transiliense desert. The influence of different grazing exclusion lengths on the percentage of soil organic nitrogen was researched using a control, one grazing-exclusion year, four grazing-exclusion years and eleven grazing-exclusion years. Compared with the control, the content of total soil nitrogen significantly decreased in 5-10, 10-20 and 30-50 cm of soil depth and the content of total nitrogen in 0-50 cm of soil depth appeared first to decrease then increased with the increase in grazing-exclusion years. The particulate organic nitrogen was highest in 0-5 cm of soil depth after eleven grazing-exclusion years, with a significant increase in the accumulation of particulate organic nitrogen distribution ratios in soil depths of 5-10 and 20-30 cm. Light fraction organic nitrogen significantly increased in 0-20 and 0-5 cm of soil depth, while it reached the highest after four grazing-exclusion years. The soil microbial biomass nitrogen appeared first to decrease then increased in 0-50 cm of soil depth. Comparing four grazing-exclusion years with the control and one grazing-exclusion year, soil microbial biomass nitrogen distribution ratio significantly increased in 5-10 cm and 20-30 cm of soil depth. Correlation among grazing-exclusion years with light fraction organic nitrogen in 0-10 cm of soil depth and light fraction organic nitrogen distribution ratio in 0-50 cm of soil depth was significantly positive. In conclusion, the content of total soil nitrogen was not recovered, but light fraction organic nitrogen, particulate organic nitrogen, soil microbial biomass nitrogen and their distribution ratios increased after short-term grazing exclusion (1~11 a) in moderately degraded S. transiliense desert.