牦牛放牧率对江河源区混播草地土壤含水量及地上现存量的影响

Effect of Stocking Rate on Water Content of Soil and Standing Crop in Elymus nutans/Puccinellia tenuflora Mixed-Sown Pastures in Yangtze and Yellow River Headwater Region

江河源区披碱草／星星草混播草地放牧试验结果表明：随着放牧率增加，各月不同土壤层含水量呈减小趋势；地上现存量的峰值降低，峰值出现的日期也提前，对照是80d（从实验开始计），极轻度～重度放牧依次为70、66、57和38d；披碱草的地上现存量和比例均呈下降趋势，而杂类草和星星草的地上现存量呈二次曲线变化趋势，且它们的百分比组成呈上升趋势；星星草地上现存量的最大值出现在轻度（5．26头／hm^2）和中度（8．0头／hm^2）之间，而杂类草的最大值出现在中度放牧附近（8．07头／hm^2），这说明江河源区混播人工草地的适宜放牧率是中度放牧，适宜牧草利用率是60％。

The result of the trial in the mixed-sown pasture of Elymus /Puccinellia tenuflora in the Yangtze and Yellow River headwater region showed： with the increase of stocking rate, water content of soil for different soil stratums from June to September in 2003 was decreased; the peak value of the existed crop was decreased and the date of peak value was advanced, which was 80d earlier than CK, 70 d for extremely light grazing, 66 d for light grazing, 57 d for moderate grazing and 38 d for heavy grazing after trial was begun respectively. For different functional groups, the standing crop and percentage composition of Elymus natans were decreased and the standing crops of Puccinellia tenuflora and weeds appeared the second degree curve, but the percentage composition of them was increased. The regression equation the standing crop of Puccinellia tenuflora was maximized when stocking rate was 6.36 heads/hm^2, which was between light grazing（5.26 heads/hm^2） and moderate grazing （8.0 heads/hm^2）, the maximum standing crop of weeds was near moderate grazing in 8.07 heads/hm^2,which indicated that aboveground biornass removed to 60% was feasible in mixed sown pastures of perennial grasses in Yangtze and Yellow River headwater region.