一、试验地概况试验设在甘肃草原生态研究所庆阳黄土高原试验站,位于东经107°50′23″,北纬35°39′24″。海拔1260米。冬春寒冷干燥,夏季炎热,年平均气温8—10℃,极端高温39.6℃,极端低温-22.4℃。年降水量320—660毫米,其中约65%以上集中在7、8、9三个月,年均蒸发量为1,100—1,500毫米。年日照时数为2,300—2,700小-时。早霜在10月中旬,晚 I. Overview of the Experiment The experiment was located in the experimental station of Qingyang Loess Plateau in Gansu Grassland Ecology Institute, located at 107 ° 50’23 “E and 35 ° 39’24” N. 1260 meters above sea level. Cold and dry in winter and spring, summer hot, the annual average temperature of 8-10 ℃, extreme high temperature 39.6 ℃, extreme low temperature -22.4 ℃. Annual precipitation 320-660 mm, of which about 65% concentrated in the 7,8,9 three months, the average annual evaporation of 1,100-1,500 mm. Annual sunshine hours 2,300-2,700 small - hours. Early frost in mid-October, late