Effects of climates factors on pasture yield of alpine Stipa steppe

Based on everyday meteorological records in reproductive period and annual grass yield of Stipa sareptana var. krylovii in alpine steppe from 1999 to 2009 in Xinghai county, Qinghai province. We used quintic polynomial to fit the trend of S.sareptana var. krylovii yield in 11 years, calculated their meteorological yield and relative meteorological yield, and also analyzed the correlationship between meteorological factors of different time in grass growth period and relative meteorological yield with DPS statistical software. The main findings were as following：Mean and accumulated atmospheric temperature in late August contributed the most to S.sareptana var. krylovii yield (P0.05), and other factors contributed less, including precipitation in late April, temperature of ground not deeper than 10 cm in early May, mean and accumulated atmospheric temperature in early June, temperature of ground not deeper than 5 cm and 10 cm in early June, temperature of ground not deeper than 10 cm in late August (P0.10).Through analysis of multiple linear stepwise regression, we found that the factors, such as mean temperature in early June and late August, accumulated temperature in middle April and early June, and precipitation in late May, were correlated negatively with relative meteorological yield of S.sareptana var. krylovii. As they increased by one unit, relative meteorological yeild would decrease by 8.15, 11.65, 0.43, 0.55 and 0.33 kg/hm2 respectively. The factors, accumulated temperature in early July, and light hours in middle and late April, and late June, were correlated positively with relative yield of S.sareptana var. krylovii. As each factor increased by one unit, relative meteorological yield would increase by 1.3, 0.074 5, 0.785 0, and 0.137 0 kg/hm2 respectively.