| On the basis of analysis and in laboratory and field, the random model of rainfall process, the principle of water requirement and botany characteristic of alfalfa in the suburb of Beijing were studied elementarily in the thesis. The main conclusions were: (1) The AR(1) model with P-III distribution was built to face practical application, and the statistical test of the rainfall process showed that the simulated results of the model matched very well with that of the measured. (2) During the experiment, the total quantity of rainfall in 2002 was 399.4 mm, the gross quantity of irrigation 80 mm, and the alfalfa grow well. The water requirement of the alfalfa, therefore, could be satisfied by irrigation measures under the similar year as typical year in this district. (3) The seasonal change of soil water for alfalfa was divided into the four stages: soil water losing stage of spring, soil water alternating stage between adding and losing of summer, soil water adds stage of autumn, soil water agglutinating stage. Lower soil water could distinctly compensate for the top soil in the first stage and the rainfall did so in the third stage. (4) The results of the experiments showed that the two kinds of alfalfa (Medicago sativa L."Zhong mu NO1" and Medicago sativa L."Gen xuan") were of higher yield and better characteristic, therefore ,should be popularized in the suburb of Beijing. The other two kinds of alfalfa (Medicago sativa L."Qing lai" and Medicago sativa L."Long dong") should not be plant in the suburb of Beijing because of the lower yield. Moreover, the results indicate that the influences of crop height, leaf length and leaf width on the yield of single trunk of alfalfa are relatively bigger and the divarication amount and leaf length were the main obstractive factors of the yield. The fitting function and need form experiments could provide consulting valuation for building the water-uptake-by-root function.
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