The Influence Of Collecting Yak Dung On Soil Nutrients And Vegetation In Alpine Meadow

Yak is the main economic breeding livestock in alpine meadow on the Qinghai-Tibet Plateau, and yak dung is the important life energy source for local people. In recent decades, yak dung was not only picked up as fuel, but also be utilized by nomads as an economic resource. Collecting dung with a long-term and a large amount would increase ecological risk on the nutrient balance of grassland ecosystem. Because of the less researches on collecting yak dung, this thesis was focused on the the influence of collecting yak dung to grassland ecosystem. Decompositing rate of yak dung and its impacts on soil nutrient and vegetation in alpine meadow were researched, the results could provide theoretical basis for reasonable utilization of local yak dung resources and protection of grassland ecosystem.1) In this study area, an adult yak ate grass with 20-23 kg/d, drank water 10-12.5 kg/d and defecated dung with 1 to 2 times. Collection yak dung term might be 3-5 days in clear day, and 5-7 days in cloudy day. Yak dung contributed about total nitrogen 548.62 kg/ha, total phosphorus 147.63 kg/ha, total potassium 131.67 kg/ha. The amounts of nutrition input and loss on beach were higher than those on slope areas.2) The water content of fresh yak dung was 84.42% and lost 57.37% after the dung was excreted in vitro 10 days. In autumn, the dung dry matter dropped to 24.85% of fresh dung after excreted 60 days later. Most of the dung nutrients had entered recirculation system in grassland. The dung significantly affected soil microbial quantity that increased mainly in 30 days to 60 days. Fungi and actinomycetes in dung affected soil depth to 8 cm within 5 days, while bacteria affected to 24 cm.3) Yak dung decomposition was the range of influence on vegetation height of 4.63±0.45 cm. The effects on soil microorganisms were conditioned by the mixing degree of dung and soil. The more even of dung and soil mixture was done, the more obvious of microbial biomass increased, and vice versa.4) Dung collection impacted on soil nutrients mainly occurred in the upper soil layer(0-7.5 cm), and no more effects in 7.5-15 cm. In the layer of 0-7.5 cm, the content of ammonium nitrogen, available potassium in the beach and the content of nitrate nitrogen, ammonium nitrogen, available phosphorus on the slope were significantly lower in full dung collection area than those in none dung collection area. The content of organic matter on the beach and the slope was significantly higher in none dung collection area than that in full dung collection area.5) Dung collection affected to soil microorganisms. In the beach, three upper layer soil microbial quantitits in dung collection area were lower than those in none dung collection area. In 7.5-15 cm soil layer, the quantity had no difference between the full dung collection and none dung collection area. The quantity of microbial was not affected by full yak dung collection between 0-7.5 cm and 7.5-15 cm soil layers.6)Dung collection impacts on vegetation composition and diversity showed a hysteresis effect, but the influence on grassland productivity was obvious and the productivity was significantly improved. In the beach the biomasses were 178.96 g/m2 and 200.92 g/m2 in full and none dung collection area respectively. In slope grassland, the biomasses were 174.64 g/m2 and 192.44 g/m2 in the full and none dung collection areas respectively.