Comparative studies on the influence of chemical fertilizer application and enclosure on alpine steppes in Qinghai Lake area IISeasonal and Annual Biomass Dynamics

The study was conducted in the sheep breeding farm of Sanjiao city in Qinghai Province, which located in the northern bank of Qinghai Lake. Nitrogen and phosphor fertilizer were applied to the alpine steppe to find out an approach to restoring degraded grassland, the natural alpine steppe at the outside of the fence was used as control. The result showed that the aboveground biomass increased significantly after applying chemical fertilizes and enclosure, the effect of fertilizer was better than that of enclosure. The seasonal dynamics of aboveground biomass is a growth curve with single apex, and the forms of the curve were similar under different treatments. The trend of aboveground biomass took the same pace with the change of precipitation and temperature. The rate of dry weight had obviously changed with season under different management. The dry matter was higher at the initial and later stages than that of middle stage, showing a high-low-high change process.