Effect of Grazing Intensities on Primary Productivities and Nutrient Seasonal Dynamic of Deyeuxia angustifolia Meadow in Sanjiang Plain

Primary productivity and seasonal dynamics under different grazing intensities were studied for a Deyeuxia angustifolia meadow in Heilongjiang province to provide a theoretical basis for the resource sustainable use of Sanjiang plain.No grazing,light grazing(0.87 cows·hm-2),moderate grazing(1.42 cows·hm-2) and heavy grazing(1.94 cows·hm-2) were designed as four treatments during the grazing season(mid-June to September).Each treatment had six mobile cages and three repetitions.Aboveground standing crop of inner and outside cage and nutrition content of community plants were measured each month.Results showed that aboveground net primary productivities declined with increased grazing intensities;light grazing had no significant difference comparing with no grazing;moderate and heavy grazing were 45.16% and 52.82% lower than no grazing(P0.05).The maximum aboveground standing crop occurred at mid-July under all tested grazing intensities,followed by mid-August and the lowest one occurred at mid-September.The contents of crude protein,acid detergent fiber decreased and the content of crude fat increased with the increasing of grazing intensity.The calcium contents of light and mediate grazing plots were higher than that of no grazing and heavy grazing.Phosphorus had an obvious change regularity with increased grazing intensities which first increased then decreased.The maximum phosphorus content(0.67%) occurred at moderate grazing in August and was 48.89% and 55.81% higher than that in June and September,respectively(P0.05).