Effects of Grazing Intensity on the Aboveground Present Biomass and Dynamic Changes of Nutrient Components in Deyeuxia angustifolia Meadow

A experiment with three grazing intensities(light grazing,0.99cows·hm-2;moderate grazing,1.65cows·hm-2;heavy grazing,2.30cows·hm-2)was conducted during the grazing season(from late May to late September)in Sanjiang Plain in Heilongjiang Province.The experiment aimed to observe the effects of the three grazing treatments on aboveground present biomass and nutrient component changes in the third experimental year in Deyeuxia angustifolia meadow,using no grazing area as a contrast.Compared with no grazing area,the average amounts of the aboveground present biomass in light grazing area,moderate grazing area and heavy grazing area significantly declined by 39.94%,44.11% and 48.71% respectively(P0.05);Differences among the three grazing treatments were not significant(P0.05).The seasons in which the aboveground present biomass was maximal in different zones varied due to grazing intensities:in the light grazing area occurred in July(the same as no grazing area),but in the moderate grazing area and heavy grazing area occurred in June.As the experiment continued,the amounts of crude protein in plant communities increasingly grew and yet the amounts of crude fat deceased.The increase of calcium of plant communities in the moderate grazing area was the highest.At the end of grazing,the amounts of phosphorus reached a peak.