不同放牧强度对多年生黑麦草—白三叶草地群体密度的影响

在中、高放牧强下黑麦草分蘖密度略有下降，而在低放牧强度下则有所上升。白三叶枝条密度受放牧强度影响较小。秋季的重牧使黑麦草分蘖密度极显著下降（P＜0．01）。6月份随着放牧强度的增强黑麦草案死亡数显著减少（P＜0．05），草地群体密度亦随之减少（P＜0.05）。在秋季随着放牧强度的增大黑麦草单蘖重明显减少（P＜0．05）。黑麦草和白三叶的单菜（枝）重与其密度均呈强负相关（P＜0．01）。白三叶的单枝重与生物量呈正相关（P＜0．05）。以上分析表明，中等放牧强度（70％利用率）有利于保持合理的草地群体密度和较高的生物量。

The Effect of Population Density in the Perennial Ryegrass/White Clover Mixed Swards under Different Grazing Intensity

The tiller density of perennial ryegrass decreased under medium and high grazing intensity,and increased under low grazing intensity. The little effect happened with the branch numbers of white clover under various grazing intensity. In the autumn, high grazing made the tiller' density of perennial ryegrass decreased significiantly (p<0.01). In early June, the dead tiller of perennial ryegrass decreased significiantly with the grazing intensity increasing (p<0.05), and the population density of pasture also decreased (p<0.05). With the development of grazing intensity, each tiller weight of perennial ryegrass decreased significiantly (p<0.05) in the autumn. Each tiller weight of perennial ryegrass and white clover were corrected negatively strong with their density (p<0. 01), and the til1er weighe of white c1over negatively positively withtheir biomass (p