Abstract: The time course of soil and vegetation changes after fencing for grazing prohibition has become a research focus of the science community and research results are used by the Chinese government for decision-making in land use planning. This study investigated the effects of fencing and grazing exclusion for 6, 10, 15 years on soil ped size distribution and on soil carbon and nitrogen storage in sierozem and aeolian sandy soil types of typical desert grassland in Yanchi County, Ningxia Autonomous Region. It was found that: 1) Fencing increased the content of fine peds in both sierozem and aeolian soil types. In the sierozem soil, structure change characterized by an increase in fine peds was most obvious after 6 years and then decreased with increasing time fenced. By contrast, in the aeolian soil the incidence of fine peds was greater at the site fenced for 15 year than at the site fenced for 6 years. 2) The contents of carbon and nitrogen (organic carbon, total carbon and total nitrogen) in soils at sites fenced for 6 years was higher inside than outside the fencing encloures, but there were no significant differences between the inside and outside of the fencing enclosures, in carbon and nitrogen contents of soils at sites fenced for 10 and 15 years. 3) The carbon to nitrogen (C∶N) ratio in sierozem soils fenced for 6 years was higher than that outside of the fence, but there was no such effect seen at sites fenced for 10 years and 15 years. The fence did not affect the (C∶N) ratio in the aeolian sandy soil. In summary, fencing can influence soil structure and ped size distribution. but the response trajectory over time differs between soil types. The optimal fencing duration to promote grassland recovery should be determined according to the degree of degradation and soil conditions at each site.

Key words: closing period, desert grassland, typical soil, soil particle, carbon and nitrogen storage