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In recent years, the grassland ecosystem is deteriorating, and up with the rapid population growth and rapid economic development, the increasing scarcity of water resources. Mu Us Sandland is arid and semi-arid areas, harsh climatic conditions, water shortages, Wushenqi is located in the hinterland of the Mu Us Sandland, the region's economic production of livestock face the dual pressures of economic development and ecological environment must be improved water use efficiency, water, grass, livestock contradiction to seek a path of sustainable development. The main objective of this study is that alfalfa own physiological point of view, to explore the growth and yield of the reaction on the degree of water deficit and deficit stage, research is applied to the different growth stages on the different levels of water deficit and re-rehydration growth and production of compensatory growth effect, calculate the different growth stages of the crop water demand, looking at each growth stage of crop moisture sensitive indicators, clear alfalfa theoretically the feasibility of the implementation of regulated deficit irrigation, and the basis for the implementation of regulated deficit irrigation; determine alfalfa optimal of Regulated Deficit period and Deficit Degree, a limited amount of water to be allocated on a reasonable basis to the various growth stages to improve the efficiency of the unilaterally water production, the establishment of the Mu Us Sandland alfalfa index system of regulated deficit irrigation (efficient water utilization system). In this context, the growth of alfalfa in Wushenqi Tooker town of Sha Research Center, of fertility indicators as well as water consumption regularity field trials, and the following conclusions: (1) under water deficit, alfalfa alfalfa drought-hit yield, plant height, Ren Yisheng sterile stage compared with full irrigation treatment of small. When affected by drought the same degree of branching ~ bud affected by the drought's impact than turning green, flowering period of water shortage affected; affected by the drought stage the same light drought treatment affected less than in the dry, but they no significant difference with CK treatment, severe drought treatment were the worst affected, and CK existence of significant differences. The bud period the Regulated Deficit moderate previously showed alfalfa the compensation growth effect, the Alfalfa appropriate moisture content and lower limits shall not be less than (40% of 50%) θf. (2) alfalfa water requirement rules change with the growth period, the overall trend is \achieve the highest 5.77mm / d after the flowering period, water demand strength and reduced. (3) alfalfa water consumption and water use efficiency was the relationship between the parabola, yield and water use efficiency of water consumption has not synchronized when water production efficiency has reached the highest value, the yield is still with the water consumption the increase. Therefore can not blindly pursue the largest output, while seeking a higher yield of the harvest, but also focus on improving WUE, to seek a balance between the two, and maximize the effectiveness of limited water resources. (4) comparing the five kinds of crop water production function, determine to select Jensen model to express the relationship between the Mu Us Sandland alfalfa yield and water consumption. The sensitive index analysis Jensen Model calculable seen alfalfa growth stages moisture sensitive level of sequence order of branching stage, bud period, the flowering period, reviving period. (5) In accordance with the principle of regulated deficit irrigation, the basis of the establishment of the the Jensen crop - water model, using a dynamic programming method, worked out the alfalfa regulated deficit irrigation system, in order to put a limited amount of water irrigation of alfalfa water deficit most sensitive period of time, to thereby obtain a relatively high yield. The results show that the year the suitable irrigation amount was 350mm, the relative yield of up to 0.9299; When available water is small, you should ensure that the branching of the irrigation water to bud.
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