| In the Qinghai-Tibetan Plateau, previous utilization pattern of the perennial artificial grassland i.e. cold-season grazing or hay harvesting is changed by yak grazing in warm-season in order to increase off-taking of yak and to minimize grazing pressure to native rangeland. Therefore, in alpine meadow region Dawu, Guoluo Tibetan autonomous prefecture with altitude of 3719m, annual average temperature of-0.7℃, annual average precipitation of 490mm and growth duration of 162d, experiments on yak grazing artificial grassland have been initiated 2001-2003 to study mutual impact of grazing between calves and grassland, and to find out effective grazing system for the artificial grassland in the region. The results are as following.1. In alpine meadow region in the Qinghai-Tibetan Plateau, percentage of sown grass species was maintained stable in grazed grassland. The highest monthly air-dried dry matter (air-DM) was 3198.8kg/hm~2 in rotationally grazed grassland, and 3023.2 kg/hm~2 in the continuously grazed grassland, 1328.8 kg/hm~2 in the continuously grazed rangeland.2. Amount of defoliation in grassland was higher than that in rangeland; in rotationally grazed grassland the amount was higher than that in continuously grazed grassland. The amount of defoliation of the yearling yaks was 302. 76kg/yak in continuously grazed grassland, 314.29 kg/yak in rotational grazed grassland and 301.45 kg/yak in continuously grazed rangeland; the amount of the 2-year-old yaks was 505.75 kg/yak, 515.64 kg/yak, 494.23kg/yak respectively. Grassland utilization was reasonable below 50% when the stocking rate was 4.6yaks/hm~2. Average growth rate (AGR) and relevant growth rate (RGR) increased in grazed grassland; AGR and RGR was higher in rotationally grazed grassland than in continuously grazed grassland, and was higher in grassland that in rangeland. AGR in grassland grazed by the 2-year-olds was higher than in grassland grazed by the yearlings. The highest AGR was 2.32 g/d ? m~2 in grassland rotationally grazed by the 2-year-olds3. Grazing has impact on growth of grassland in second year as well. Seed emergence has been promoted in rotationally grazed grassland. Fresh yield and air-DM of sown species, Elymus nutant, in the second year of the rotational grazed were 5088.88kg/hm~2 and 3053. 33kg/hm2 respectively and seed yield of in the rotational grazed was 480kg/hm~2, which were significantly higher than those in the continuously grazed grassland and the non-grazed grassland. Fresh yield of forbs in the rotational grazed artificial grassland was 193.33kg/hm~2, lower than that of the continuous grazed and that of the non-grazed check. Forbs were inhibited in the rotational grazed artificial grassland.4. Yaks' time for traveling in defoliation was 11.15min in the continuous grazing, 10.6min in the rotational grazing and 12.95min in the non-grazing. Time for defoliation was 33.06min in the continuous grazing, 37.9min in the rotational grazing and 34.61min in rangeland continuous grazing. Time for the resting was 14.26min in the continuous grazing, 13.97min in the rotational grazing and 12.09min in rangeland continuous grazing. Defoliation DM during 11:00 - 12:00 was 0.78kg/h~1 in the continuous grazing, 1.28kg/h~1 in the rotational grazing and 0.791kg/h in rangeland continuous grazing.5. Gains of yak calves during June to October grazing grassland were higher than those grazing the native rangeland. Total gain of the yearlings was 27.52kg in grassland continuous grazing, 32.27kg in grassland rotational grazing and 25.04kg in rangeland continuous grazing, those of the 2-year-olds was 32.18kg, 33.72kg and 29.93kg respectively. The daily gain of the yearling... |
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