Seasonal Dynamics Of Nutrients In Soil And Forage Of Alpine Meadow Under Different Cultivations On Qinghai-Tibet Plateau

The aipne meadow in Sanke Township, Xiahe County, Gannan Tibetan Autonomous Prefecture of Cansu Province was selected and designed 4 treatments(continuous grazing, reseeding, fertilization and non-grazing) to study the seasonal dynamics of nutrients in soil and forage, and the forage quality was evaluated as well. The main results are as follows:1. The diffeferece of soil bulk density among treatments was significant. Soil moisture content was the lowest in May ranged from 11.92% to 16.62% in 4 treatments and it reached the highest in September ranged from 17.55% to 39.18%.2. The contents of soil total N, total P, total K and organic carbon significantly varied among seasons. The total N content varied from 0.32 mg/kg to 0.6 mg/kg and it was the lowest in May(0.35 mg/kg) and highest in September(0.48 mg/kg), and among treatments, it was highest in grazing treatment(0.47 mg/kg) and the lowest appeared in enclosure treatment(0.36 mg/kg). The soil total P contents in all treatments were low(ranged from 0.03 to 0.07 mg/kg) and no significant difference among treatment. The soil total K contents in all treatments were high(ranged from 9.07 to 41.92 mg/kg). Soil organic carbon(SOC) content decreased along with the soil depth and it was the highest in grazing treatment in June(42.65 mg/kg).3. The height, coverage and biomass of vegetation increased along with the growing season and the enclosue treatment showed great positive impact. Among 4 treatments, the low coverage and less plant species and low primary productivity were in grazing treatment, while the high coverage and more plant species were in enclosue treatment.4. Crude protein content in forage was the highest ranged fron 1.58% to 3.46% in returning green stage, and it gradually reduced along with the growing season. The content of crude fiber and neutral detergent fiber was stable and ranged from 28.61% to 30.73%. The crude fat content was low and no obvious variation pattern was found. The crude ash content showed an obvious variation pattern, and along with the season, it decreased first and then increased for Gramineae and Leguminosae. The content of nitrogen-free extract gradually increased along with the season, and the lowest appeared in returning-green stage and the highest in withering stage. Ca and P contents were higher from May(12.95mg/kg t00.21mg/kg) to July and lower from August to September(0.41mg/kg to 0.05mg/kg).5. The biomass showed a significant negative correlation with crude protein content and a positive correlation with crude fiber content. The nutrient balanced price of legumes was the highest(2.87 to 4.96). In general, the nutrient in forage could not meet the demand from livestock and the supplementary feeds were neccassary.