| This paper introduces alfalfa's growth patterns, water consumption characteristics and regulated deficit irrigation model in desert oasis of Gansu province. The experiment was conducted in the farm of the center of agriculture and technology in Minqin county, Gansu province. According to the production practical in Minqin, carried out the experiment in the different growing periods(70%, 55%, 40% of field capacity) of different cutting and the first cutting under water deficit, which controlled by lower limit of soil water content. When soil water content under 80cm reached the lower limit to irrigation, the upper limit soil water content is 90% field capacity. According to the cultural characteristics and physiological feature of alfalfa, the harvest of alfalfa have three cutting. The first cutting for growth period are: growth stage, branching stage, budding stage, initial flower stage. The experiment set up 11 treatment groups, three repetitions were required in each intensity. We use first cutting single stage combination with whole growth period water deficit, and whole year different cutting in single stage combination with every cutting water deficit. The experiment were carried out from Apr. 15th to Sep. 30th, the experiment periods last 168d, the results as follow:(1) According to the study of alfalfa's growth in the aerial and underground parts of the plants show that: different growth have inhibition role to height, stem diameter, area of leaves, root crown diameter, depth in soil. Milder deficiency irrigation level increase a lot of lateral root and branch number, after the rehydration, height and area leaves present compensatory growth. As to the first stubble, especially for light water stress(55%θf)before budding stage, it have benefit to root growth, optimal canopy structure. It is important to alfalfa have a whole harvest.(2) Different water deficit in different degree will reduce the growth of leaves transpiration, photosynthesis and leaf conductance. Different water deficit in different stage will increase the WUEL in this stage. Transpiration, photosynthesis and leaf conductance are double-peak curve except for branch photosynthesis is unimodal. The appearance time of wave crest and the wave trough have little different. Leaves transpiration and photosynthesis have a different degree to leaf conductance. With the increase of leaf conductance, leaves transpiration have a same increasing extent with photosynthesis. But when the leaf conductance exceeds some value, the increasing rate of photosynthesis is slowered obviously and even have a large decrease. The alfalfa begin to enter luxurious transpiration stage from the perspectives of photosynthetic product. WUEL is increased by water deficit before budding stage.(3) There is changes in soil moisture: alfalfa can obtain effective water use in the 0~180cm soil moisture, the changes of the high water treatment is more obvious, draws water the function to be more obvious.(4) The water consumption analysis indicated that water consumption rate express a tendency which the cutting decreases progressively, there is a number of water consumption in the first cutting, water consumption reaches maximum value in the budding stage, branching stage next best. Relationship between irrigates quantity and the water consumption are analyzed that the water consumption is increased with irrigates the quantity increased, but the same irrigate quantity, different time of the irrigation will have the tremendous influence to the water consumption. Value of Crop coefficient of alfalfa is unimodal change curve which increases first, reduces, the crops coefficient's maximum of the different soil moisture content processing presents the flowering initial period, and by cutting decreasing progressively. (5) The first cutting passes through owes certainly the water stress treatment on alfalfa, its yield is close to comparison, before budding stage, carrying on deficit are dealing with 2,3 of the compensation effect. The annual yield's analysis indicated that the alfalfa yield in the annual various cutting time change rule is, decreases progressively by the cutting and yield of the first cutting is about 50 percent of the total. the first cutting offer mildly water processing 8, displayed the obvious compensation growth in the successor cutting, compared increased production 5.08%, reached 14218.5kg/hm2, the first cutting gave the mild stress, caused the crops experience, Promote root system to grow, was advantageous to the successor cutting time and the annual ultimate yield, but processing 11 of the first cutting Severe stress in the earlier period has Inhibited alfalfa's growth seriously, after the rehydration compensatory growth has also been severely inhibited. The yield, water use efficiency and the water consumption assume obvious two parabola relations, the yield at first increase along with the increasing of water consumption. When the water consumption is bigger than some value, the yield increases along with the water consumption reduces. The yield and the water use efficiency don't have the synchronism to the water consumption change, namely usually when water use efficiency is already maximizing, the production increase in water consumption is still increasing.(6) According to crop water production function model of the first cutting of alfalfa and the annual water production function shows that Blank model, Stewart model and Jensen model are more reasonable. Sensitive index of water shortages showed that the branching stage and budding stage are period of dry sensitive stage, followed by the early flowering, once again turning growth stage. And found that a certain period in reviving the water stress, the crop can play a role in the growth of training, access to higher yield.(7) Guidance for the production of irrigation system have three harvest and four irrigation in years. Irrigation requirement is 750m3/hm2～900m3/hm2, The irrigation of the first cutting is 2 times, The irrigation of the second and third cutting is 1 time. Irrigation should not be too early. the certain degree of the water deficit in growth stage make alfalfa be certain exercise of the growth. The branching in the early(In early May) and budding in the end (In early June) of the first cutting irrigate. Don't irrigated is good for harvest in flowering stage. The water distribution programmers and the actual conditions of local production, can reach a high yield and maintain a higher water use efficiency, play important role in water saving.
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