Study On Optimum Grazing Method Of Yak In Alpine Meadow Pastureland

The trial was conducted in alpine meadow pastureland, in Jianshe Township, Dari County, Guoluo Tibet Autonomous prefecture, Qinghai province. It studied effects of stocking rates on aboveground biomass, composition of vegetation, soil nutrient contents and growth of yak in alpine meadow pastureland. The result as follows:The different stocking rates have obvious effects on growth of yaks during trial period. Justified from comprehensive analysis of effects of stocking rates on growth of yak. the moderate grazing is optimal. Whatever is the growth of summer pasture, or winter pasture, or the whole year, stocking rates had not notable effects on the growth of yak. The second year (from the 1st June of 1999 to the 31st May of 2000), it is obvious that with the lightening of stocking rates the daily gain of yak increased, as showed that stocking rate had been key factor of yaks' growth. By statistic analysis, the total gain between light and moderate grazing did not have significant difference, but compared with heavy grazing, they had significant difference with heavy grazing.By analysis of linear and non-linear, in Qinghai-tibetal plateau alpine meadow pastureland, optimum matching of rates for twice-rotation pastureland is: summer pastureland is 1.71 yaks/hm2, and winter is 0.74 yaks/hm2.Under the different stocking rates, on summer pastureland or winter pastureland, with the increase of stocking rates, the ratio of high quality forage reduced, otherwise weed increased. Total coverage of vegetation for three treatments all increased. Coverage of the light and moderate grazing for the high quality forage increased, and coverage of weed reduced. But as for the heavy grazing, the result was contrary.Under the different stocking rates, dominant species of plants lied in difference,and the changes of the similarity coefficient of the community were different. After a year, dominant species on the pastureland with light and heavy grazing did not change, but that with moderate grazing changed. The ratio of weed and high quality forage was different.The similarity coefficient (SM) is larger (0.7918) between light grazing treatments contrast, and the smallest (0.5338) between heavy grazing treatment and contrast. H ' is the largest under the moderate grazing, the smallest under contrast, and the light and heavy grazing are between them. J ' is the largest under the light grazing, the smallest under the heavy grazing.With the increase of stocking rates, the nutrient contents of soil including organic matter, N, P, NOs-N, available P, have certain change, especially N, and then organic matter. The classes of change for the nutrient contents of soil are 0-5cm, 5- 10cm, and then 10-20cm.Among the components of nutrient contents of soil, only P is with a significant difference between the different stocking rates (P>0.001).