| Because of unique natural climate condition in the Qinghai-Tibetan Plateau, there are not many adaptable forage cultivars for artificial grassland. Among those adaptable cultivars, forage yields and quality vary greatly with different cultivation methods. To exert fully productivity of the cultivars, the study on manipulation and composition of the mixed field of annual grasses and legumes in alpine region was carried out 2001-2003.3 trials were conducted in 4 different ecological areas, which located around Qinghai Lake, Chaidamu Basin, southern Qinghai, eastern Qinghai. In trial 1, agronomy study was conducted in mixed communities made of 4 annual grasses and 4 annual legumes. The structure of the mixed community and biomass production under different seeding rates was studied in the trial 2. In trial 3, optimal seeding dates in different ecological areas were studied as well.Data on growth, nutrition contents and biomass were collected and analyzed by means of AHP and the path analysis. Optimal mixture of annual grasses and legumes, plant community structures, competition between species, rate of biomass accumulation and optimal seeding date were studied. It is expected that relevant theory and techniques were found out for forage production in the area.1. Literature review indicated that it is necessary to work out appropriate species composition of annual grasses and legumes with high yield and quality in the Qinghai-Tibetan Plateau. However, species and the composition of the mixture, the structure of the plant communities and proper seeding date remained unknown in the mixed artificial grassland.2. Productivity, nutrient contents and botanic characters appeared excellent in the mixture of annual grasses and legumes in the Qinghai-Tibetan Plateau. Hay yield and crude fiber output of the single grass species were 6953 kg/hm2 and 1496 kg/hm2 respectively in blooming stage, crude protein yield was 489 kg/hm2 in heading and early blooming stages. However, among 16 mixtures in the study, the lowest hay yield was 9000 kg/hm2 occurring in the mixture of barley and legumes T5-T8; the highest hay yield was 21000 kg/hm2 in the mixture of sweet oat and winter vetch (T9). Crude protein and crude fiber output were 636.5-3004.8 kg/hm2 and 1323-1773 kg/hm2 respectively. The hay yield in the mixture was much higher than in the single species field; ratio of stem to leaf, ratio of fresh forage to hay, root length and root weight in the mixtures were superior to the single species field. It is indicated that all the good performances have resulted from positive competition andpromotion of each community species, which has improved utilization of solar radiation and soil nutrient, biomass accumulation.3. Productivity of different mixtures varied significantly, mainly in terms of phenology, seasonal appearance, structures of the mixture at different height, ratio of stem to leaf, ratio of fresh forage to hay, water content and effect of root distribution on nutrient content and on forage yield. Quantities of the above parameters could be used as criteria for evaluating the mixture, consequently, optimal mixtures could be selected. In order to avoid extreme items in selection, AHP method was used to estimate occurrence of all the items, each item has been examined separately.4. Among the optimal mixtures of annual grasses and legumes, sweet oat+ vetch Ximu880 (T10) and rye grass+pea (T4) have the longest phenological stage, suitable to the area around the Qinghai Lake and the Chaidamu Basin. While Qinghai 444+vetch Ximu880 has shortest phenological stage, suitable to the area in southern Qinghai, the area in eastern Qinghai.5. Trials on species composition in the mixture were conducted after the optimal mixtures were selected. The compositions were made of 1 oat composition (135 kg/hm2) to 3 vetch compositions (75-45 kg/hm2), and 1 vetch composition (56.25 kg/hm2) to 3 oat compositions (168.75-67.5 kg/hm2). 6 compositions were compared with single species field (oats or vetch) as following:1). Hay yield and fr...
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