The
conservation tillage on soil water dynamic and water use efficiency based on two phases rotation systems with spring
wheat and field pea have been conducted in Dingxi specific semiarid hilly areas in the middle of the Loess Plateau from 2002 to 2004. The results showed that
conservation tillage enable to increase 0～200 cm water storage and soil moisture,and it is more obvious in the poor raining year than that in the rich raining year. The water storage of no-tillage and no-tillage with straw retention are much higher than conventional tillage,1.93%～7.25% and 0.06%～3.58% respectively. Fallow and rotation, which possess better storage function, are propitious to increase the using ration of rainfall. Soil moisture takes on a change of anti "S" in 0～200 cm profile. Soil moisture is higher at seeding stage, 5-leave stage and harvesting stage, while is lower at blooming stage. The crop yields and WUE of no-tillage with straw mulch are 3 709.69 kg/hm~2 and 10.45 kg/(hm~2·mm), which increased 30.28% and 40.08% respectively than conventional tillage.