Dynamics And Effect Of Nitrogen On Mixture Grassland Of Cultivated Perennial Grass In Alpine Region

The mixture grassland of cultivated perennial grasses is the best choice to improve the productivity of grassland and keep the balance of man-interfered ecosystem in the alpine region of Qinghai-Tibetan Plateau of China. Due to the harsh condition, it is not easy to maintain the productive-ecological stability of the cultivated mixture grassland. Based on the long-term observation, the stability, especially by applying N-fertilizer, of mixture grassland of cultivated perennial grass is studied. The results indicate:1. In alpine region, the productivity of the grassland can be improved by establishing mixture grassland of cultivated perennial grasses. And the ability of high productivity can be maintained for at least 3 years (or 4 years). So it is feasible and effective to use the cultivated grassland to improve the productivity in this region.2. The yield of mixture grassland can be improved by N-fertilizer. The optimum quantity of the N-fertilizer is 113kgN/hm2 for the three-grasses community and 75kgN/hm2 for the four-grasses'. Therefore, the four-grasses community is better than the three-grasses' economically.3. Based on the yields of biomass and protein, the community of Bromus inermis+ Clinehanus nutans+ Agropyron cristatum + Poa crymophila should be harvested in September, but Bromus inermis + Elyrmis nutans+Clinelumus nutans, Efymus nutans+Clinelumus nutans + Agropyron cristatum , Bromus inermis +Efymus nutans +Agropyron cristatum+Poa crymophila, Efymus nutans+Clinelumus nutans+Agropyron cristatum+Poa crymophila(M\ the above is third-year ) and Bromus inermis+Elymus nutans+Clinelumus nutans(4th year) should be in Augest.4. The density of the community, especially of the dominant components-Etymus nutans or Clinelumus nutans is increased by N-fertilizer. But the effect is not evident on that of the sub-dominant.5. The number of the 1st year old plant is increased with increasing of the amount of the N-fertilizer. It is the important to maintain the high productivity of the community.6. In the region, the optimum leaf area ratio(LAR) is 4.5-5.5 to the dominant grasses, Elyntus nutans and/or Clinelumus nutans.7. In alpine region, it should be small amount but many times to apply N-fertilizer to mixture grassland of cultivated perennial grasses.