Interactions Of Soil-herbage-livestock In Alpine Meadow-Tibetan Sheep Grazing System, Qinhai-Tibetan Plateau

Grazing is one of the most important methods to manage grassland ecosystem, and the respond model of interactions of soil-herbage-livestock to grazing is always the front edge and hot spot to grazing ecology. The rangelands on the Qinghai-Tibetan Plateau are mainly used for grazing. This study mainly concerned with the alpine meadow-Tibetan sheep rotational (SDSR) and continuous grazing systems (SLC) at Maqu county, continuously monitored physical and chemical properties of soil, characteristics of vegetation, productivity and grazing behavior of livestock during 2010-2012, and analyzed the dynamic and interactions of soil-herbage-livestock of alpine meadow-Tibetan sheep grazing system. Main results that:1)2010-2012, average monthly gain of Tibetan sheep kept at 3.5-4.5kg during July-September and it began decrease in October. Standing crop of July-September were 2.2-3.8t/ha then turned to decrease gradually. Grazing systems did not affect the Tibetan sheep performance (kg/head and kg/ha), residual herbage mass when the stocking rates were set 24SM/ha (P>0.05); Live weight gain per head for SDSR24 (short-duration seasonal rotational grazing system with stocking rate 24 SM/ha) was greater than SDSR36 and SDRS48, while live weight gain per ha showed opposite tendency. No differences were found between SDSR-HL(H,48SM/ha and L,24SM/ha) and SDSR-LH in live-weight gain per head or per ha (P>0.05), while the ratio of residual herbage mass of the warm-season pasture and the cold pasture of SDSR-LH was more than twice than that of SDSR-HL at the end of grazing period. Daily live-weight gain of Tibetan sheep decreased linearly with increasing grazing pressure in both warm and cold seasons. Grazing pressure index of 27.6,24.4,23.8AUD/t DM peak herbage mass (animal unit·day, AUD) for 2010,2011, 2012, can make sure sustainable development of the alpine meadow under the rotational grazing system, and the average "optimal grazing pressure index" of three experimental years was 25.2AUD/t DM peak herbage mass.2)From July to December during 2010-2012, Under SLC, intaking rate, foraging rate, chewing rate of Tibetan sheep decrease with prolong of the months, while the bite number per step showed opposite tendency. Besides, chewing number per bolus and interval of two boluses increase firstly and then keep no change along the prolonging of the months. The ratio of ruminating and intaking time increases with the increasing of standing crop and daily mean temperature. More standing crop and higher daily mean temperature result in the increasing of intaking rate, foraging rate, chewing number per bolus and intervals between two boluses, but decreasing of intaking number per step and chewing rate of bolus. Heavier initial live weight result in lower sensibility of foraging rate, bite number per step, chewing rate, chewing number per bolus and interval between two bolus of Tibetan sheep to average daily temperature; Heavier initial live weight contribute to decrease sensibility of bite number per step, chewing number per bolus and interval between two bolus of Tibetan sheep to standing crop.3)The results of three-year study showed that fencing increased the soil organic carbon content of soil (SOC, especially 0-10cm) and same trend was found on total nitrogen content(TN, P<0.05), but opposite trend was found on total phosphorous content (TP, P<0.05). No differences were found in the soil bulk density and soil moisture in each soil layer of fencing and grazing treatments (P>0.05).4) Compare with grazing, fencing increased population and community density and above- and underground biomass (P<0.05), modified canopy structure:fencing caused the biomass of species taller than 40cm increased and shorter than 40cm showed on different to grazing treatment (P>0.05). No significant differences were found on the species diversity during the 3 study years (P>0.05).5) Litter deposit linearly decrease with the increase of grazing pressure (P>0.001). Litter decomposability decrease with the increasing of carbon and lignin content and ratio of lignin content/N content. Variation of decomposition rate (that "in situ") can be explained 87% by the soil environment and 7% can be explained by litter quality, while the decay rate of N can be explained 2% and 71% by soil environment and litter quality.