The Effect Of Management And Topography On Vegetation And Soil Of Natural Grassland Of Loess Plateau Slopeland In Gansu Province

Loess Plateau is one of the two poorest areas in China and is one of the most serious areas of water and soil loss in the world. The rangeland mainly locates on the slopeland of Loess plateau and account for 27.3%-67.5% of soil areas and plays an important role in livestock and ecological protection.The research executed on the field station of College of Pastoral Agricultural Science and Technology, Lanzhou University in Loess plateau of the eastern Gansu province from 2005 to 2006. The purpose was to explore the effect of management methods (continuous grazing, exclosure for three years and six years), slope (0°, 15°, 30°, 45°) and aspect (shady and sunny) on vegetation (the coverage, species richness, aboveground biomass)and soil (moisture, soil respiration, soil organic carbon, total nitrogen, total phosphorus, available nitrogen and available phosphorus) and find out the key factor.Vegetation1 Vegetation coverage of rangeland increased significant after enclosing (P<0. 05) and decreased with the slope increasing( P<0. 05). The effect of aspect on coverage was not significant different (P>0. 05) .2 The high and low sequence of the annual species at any management is exclosed 6 yeasrs grassland > exclosed three years grassland > continuous grazing grassland; The perennial species was opposed to the annual species. Change of both with slope and aspect was irregular. Effect of management and topography on total species has no significant rule.3 The aboveground biomass increased with the enclosing time increasing at the same slope and aspect and decreased gradually with the slope increasing. Aspect has not obvious impact on aboveground biomass (P>0. 05) . The high and low sequence of the ratio of leguminosae biomass is exclosed 6 years grassland > exclosed 3 years grassland > continuous grazing grassland.Soil1 To different layers of soil, the soil moisture sequence is exclosed 6 years ) exclosed 3years> continuous grazing grassland, but there are no obvious regular according to theslope and aspect all grasslands, soil moisture reach the highest at July.2 During May and July, the high and low sequence of soil respiration intensity in grassland is closed 6 years ) exclosed 3 years>exclosed 3 years>continuous grazing at the same slope and aspect and as the increasing of the slope the intensity become reduce.( P< 0.05).the slope orientation have no effect on respiration speed. The max data of it appears at July. And in November the respiration speed reach highest when the slope is 15°,and the trend is increase then reduce, the management pattern and slope orientation have no influence on it.3 when the slope and orientation are same, sequence of the density of soil organic carbon is: closed 6 years >closed 3 years>closed 3 years>freedom grazing land. the density of soil organic carbon in shade slope rising by the slope, but the sunny side have no regular change, also slope orientation have no clear variance on soil organic carbon.4 Also when the slope and orientation are same, content of grassland soil nitrogen density and available phosphorous is: closed 6 years >closed 3 years>closed 3 years>freedom grazing land. Density of nitrogen and available phosphorous increase as the slope, but slope orientation have no significance affect.5 For the same slope and orientation, the general trend for total density of phosphorous and available phosphorous become increasing by the raising of closed years. Soil phosphorous show the inclination of reducing then increasing. and at the 15°become the lowest, also have no regular change as the orientation.In order to show the influence of management patterns, slope, orientation to the vegetation and soil, we use the analysis of comparing factors.then we can see from the results that the contribute rate of management to the biomass,coverage,soil respiration,density of soil organic carbon,nitrogen,phosphorous,available nitrogen,available phosphorous are: 68.42%, 72.13%, 72.11%, 67.28%, 70.25%, 61.19%, 74.37%, 67.42%, all exceed 60%,so it become the key factor which effect vegetation and soil.The result of this project has positive significance on evaluating the projects of grain for green and natural grassland protection and has scientific direction significance on natural grassland utilized rationally and sustainable development of animal husbandry.