Effects Of Grazing Intensity On Soil Nutrient In Kobresia Pygmaea Meadow Tibet Plateau

We did experiment of grazing yaks in gongbujiangda bang jie chi of nyingchi in Tibet. The experiment included heavy grazing(HG), delay heavy grazing(DHG), moderate grazing(MG), delay moderate grazing(DMG) and none grazing(NG). We measured community richness, evenness, biomass, cover, density, height and soil propert effect in different grazing intensity. The results indicated that(1)Alpine meadow vegetation communities changed significantly under different grazing intensity. Richness, total coverage and evenness decreased under heavy grazing(HG), and it was significant difference(P<0.05);Biomass is the highest in moderate grazing(MG) and delay moderate grazing(DMG), and there was significant difference between it and none grazing(NG)(P<0.05) Height, coverage and density of stipa purpurea and kobresia pygmaea were significant difference for Heavy grazing(HG)(P<0.05).(2)Water content and hardness of 0~10 cm soil, was not significant difference with none grazing(NG) under Heavy grazing(HG)(P > 0.05); Cattle trample increased, grassland hardness was larger and the soil permeability was worse with the increase of grazing intensity. Quality and volume of soil total porosity and capillary porosity increased significantly(P<0.05). It decreased with the increase of soil depth, and the difference was significant(P<0.05).(3)Available nitrogen, phosphorus, total nitrogen and total phosphorus decreased with the increase of grazing intensity. Total potassium content increased and then decreased with the increase of grazing intensity. Heavy grazing and delay heavy grazing significantly reduced the soil available nitrogen, available phosphorus and available potassium and total nitrogen, total potassium content; Soil organic matter content increased with the increase of grazing intensity gradually reduce; Soil pH was not significant under different grazing intensity(P>0.05).(4)Yak weight reduced with the increase of grazing intensity, Heavy grazing(HG) of yak weight was significant lower than the moderate grazing(MG). Yak weight increased significantly in summer(P<0.05), while yak weight increased significantly in moderate grazing(MG)(P<0.05).(5) Yak weight and total vegetation cover decreased significantly(P<0.05) with the increase of grazing intensity. Grassland biomass and Yak growth rate were the highest in moderate grazing(MG), while it decreased in heavy grazing(HG).