| Alfalfa is a forage crop with high protein, which is an important resource of plant protein. Alfalfa industrialization depends on advanced varieties, research on alfalfa quality characteristics is vital for selection and reasonable utilization of different varieties. On the basis of the predecessor's research, this experiment adopted Common nutritional tests and Detergent fiber analysis to measure respectively content of CP, EE, NFE, CF, NDF, ADF, CASH, Ca and P. Besides, dynamics of nutritional compositions of different alfalfa varieties in different cuttings, suitable cut time, correlation of quality characteristics, and relationship between quality characteristics and morphological characteristics were studied. Through analysis above, we evaluated comprehensively economic value of 31 alfalfa varieties by Analytic Hierarchy Process (AHP), in order to select advanced alfalfa varieties with high yield and high quality, and provide feasible basis for constructing grasslands in the northwest region. The results as follows:1. Main nutritional concentrations changed with developing stage of 23 alfalfa varieties in different cuttings, the concentrations of CP, EE, NFE, CASH, Ca, P and digestibility decreased, while CF, NDF, ADF content increased. Nutritional concentrations changed rapidly before beginning of flower, while changed slowly after beginning of flower. Moreover, from full bloom stage to early pod stage, CF, NDF, ADF content increased rapidly by a big range, at the same time, digestibility declined dramatically. However, changes of CF, NDF, and ADF average content of 23 alfalfa varieties in different growth stages of different cuttings were different. Namely, with advancing growth stage, Changes of nutritional compositions in range and velocity for first-cut alfalfa were bigger than those for second-cut alfalfa. For example, from branching stage to beginning of pod stage, CP content for first-cut alfalfa reduced 6.53% in range, and declined 0.13% d-1 in velocity, whereas for second-cut alfalfa respectively decreased 9.32% and 0.274% d-1.2. By cluster analysis, 23 alfalfa varieties in first cuttings were divided into four types: The first type was the best including Ameristand201, Alfagraze, Avalanche, Total, Affinity, Aggressor, Innovator, Arriba, ISRsupreme, Apollo supreme, Lobo, Beijiang; The second type was better ones including Ameriguard302, Amerigraze401, Abilence; The third type was common quality including ZhonglanN0.1, Xinjiangdaye, Archer, Deguodaye, Meiguozajiao; The forth type was poor including Xingmu N0.1, ZhongmuN0.1 and Baofeng.3. Nutritional compositions in early flower stage of different cuttings were compared; Results showed that digestibility, CP, NFE content in the first cuttings were higher markedly than those in the second or third cuttings (P<0.05). CF, NDF and ADF concentrations werethe highest in the second cuttings, comparison of them between the first and the third cuttings wasn't significant (P>0.05); EE, Ca, P content were lower relatively and had little changes than others in different cuttings. In the view of total nutrition value, quality of alfalfa in the first cuttings was finer than that in the second or third cuttings.4. Result of research on suitable cut time of alfalfa showed that yield of hay increased in the first cuttings, and reached peak in the beginning of pod stage, as growth stage proceeded. In the view of CP yield and rate of fiber to protein, alfalfa should be harvested when reaching one-tenth bloom, and completed harvest by the time when alfalfa reached full bloom.5. In the early bloom of different cuttings, Variation coefficients of digestibility, NDF, ADF, NFE, CF and CP was small, that of P, Ca and EE content was relatively bigger.6. Research on correlated analysis of quality characteristics, and relationships between quality characteristics and morphological characteristics showed that CP content was negative significantly correlated with CF, NDF, ADF concentrations (P<0.01 ); CF content positively significantly c...
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