Effect of yak grazing in warm season on perennial artificial grassland in alpine meadow

Effect of yak grazing in warm season on perennial artificial grassland in alpine meadow was studied from 2001 to 2003 on Qinghai-Tibetan Plateau.The result showed that:after grazing for 2 years,the percentage of sown grasses was 95.27% in rotationally grazed grassland,86.15% in continuously grazed grassland and 58.01% in un-grazed grassland.The highest monthly air-dried dry matter yield(air-DM) was 3198.8 kg/hm~(2) in rotationally grazed grassland and 3023.2 kg/hm~(2) in the continuously grazed grassland.Absolute growth rate(AGR) increased in grazed grassland;The AGR was higher in rotationally grazed grassland than those in continuously grazed grasslands.Grazing shown impact on growth of grasses in next year as well.Seed emergence was improved in rotationally grazed grassland.Fresh yield and air-DM yield of sown species in next year were 5088.88 kg/hm~(2)and 3053.33 kg/hm~(2) respectively in the rotationally grazed grassland and seed yield of in the rotational grazed was 480 kg/hm~(2),which were significantly higher than those in the continuously grazed grasslands and non-grazed grassland.Fresh yield of weeds in the rotational grazed artificial grassland was 193.33 kg/hm~(2),lower than those in the continuous grazed and non-grazed grasslands.