| Uncontrolled grazing over many years has been practised on Stipa grandis Steppe. The year round grazing over three seasons has gradually been replaced by two seasonal grazing, and eventually by continuously year long grazing. Thus leads grassland seriously deteriorate. In order to established a more rational system to graze on the grassland, the trial of rational grazing (RG) and continuous grazing (CG) had been practiced on S. grandis Steppe for two years. The stocking rate was designed as middle intensity of 3 sheep-unit per hectare for RG and CG. A ungrazing plot was set up as contrasted. Plant community, dominant species, sexual reproduction, and nutrient, and liveweight gain by sheep were measured periodically. I . The responses of plant community of S. grandis Steppe to different grazing systems1 .The primary production under RG is lower than the FG, and appeared as low-compensatory growth. The primary production under CG is higher than the FG and appeared as over-compensatory growth.2.The difference of standing crop is not obvious between the two grazing systems, but the difference of standing crop among different RG plots is apparent variant. The restricting grazing areas and time is adopted by RG to maintain the production of high preference plant in the expense of increasing the diet of low preference and decreasing the diet in late spring. The result showed that the above ground standing crop increased.3. The plant compensatory growth occurred ahead and lasted a long period for the reason of grazing lightness in late spring in CG plot, the time of integrated compensatory growth is deferred to CG and short for the reason of grazing heavily on some plots during late spring.4.The affecting on height of grasses is not obvious in grazing systems, but coverage and density is obvious. The coverage of CG is much higher than RG on June and August, and the density of RG is much higher than RG.5.The richness, diversity and dominance of plant under RG is similar to that under FG. The richness and diversity under RG and FG are higher than that under CG, but the dominance is lower than it under CG. The B diversity index of RG is higher than FG and CG. The coefficient of community similarity demonstrates in RG is similar to FG, the variance of FG and CG is the biggest.II. The responses of dominant species population of S. grandis Steppe to different grazing systems1 .The above ground standing crop of dominant populations under two grazing systems has no differences. S. grandis under two grazing systems have been possessed the over-compensatory on May and July (P>0.05), and low-compensatory on August and September (P>0.05). Thebiomass of 5. grandis surpassed under RG (P>0.05). The biomass of Leymus chinense under two grazing systems were low-compensatory in late spring (P>0.05), but were over-compensatory in Summer (P>0.05). So were the Cleistogenes squarrosa under two grazing systems (P>0.05).2.The characteristic parameters of dominant species population under different grazing systems appeared the great difference on July and August, the height had no difference, and the coverage showed the greatest variant. The important value of plant of the preference excellent and good were higher under RG, it was the same of preference bad plant under CG. The number of big and middle bunch of S. grandis were higher under CG than RG, and the number under RG is obviously higher than FG. The proportion of reproduction of S. grandis had raised, so do L. chinense under RG, while C. squarrosa didn't change obviously.3.The sexual reproduction affected by two grazing systems appeared no distinct variant. The available number of reproductive tiller and seed germination were decreased by grazing systems. So did the allocation of sexual reproduction and level of differentiation of reproduction of C. squarrosa and decreased, especially in seed germinating ability. The more preference forage's seed reproduction ability kept under RG, the less preference forage's reproduction ability under CG.III. Dynamics of nutrient con...
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