1979 to 1983, 103 forage species and varieties were introduced into Gansu from other provinces of China, and more than 100 species and varieties were introduced from the United States, New Zealand, Germany, Poland, the Soviet Union, and Australia (Guo et al., 1984). Sainfoin, alfalfa, Astragalus adsurgens, Agropyron cristatus, Vicia sativa, Melilotus officinalis, Sorghum sudanense, Caragana microphylla, Bromus inermis, and Symphytum peregrinum have been introduced to the Gansu loess plateau, proved to be among the best species adapted to the region, and are now being used in soil conservation and livestock production. Astragalus cicer L. from the United States is one of best forage species introduced to the loess region (Chen et al., 1984). Chen and Guo (1984) have described the introduction and cultivation of forage in various parts of Gansu. Alfalfa research has been reviewed by Wu and Zhang (1988a,b).

Techniques of forage breeding and seed testing were reported by Li (1983) and Cao (1987). Seed yield components of sainfoin were analyzed and their significance in breeding was discussed by Wang (1986). Sun and Chen (1990) have reported various testing methods for alfalfa seeds and concluded that TTC, cold test, and accelerated aging tests are more reliable than other methods. Wang Yanrong et al. (1988) have studied the effect of various treatments on germination of hard seeds of Coronilla.

The production, nutritive value, and feeding value of major forage varieties have also been studied (Wu et al., 1984; Zhu et al., 1987; Li and Liu, 1987a,b,c; Gao et al., 1987). Zhu et al. (1988) studied the nutritive value and yields of sainfoin and lucerne in Gansu and evaluated the palatability of these two species among sheep and rabbits. The nutritive components of several common grasses (Puccinellia sp., Agropyron cristatum, Achnatherum splendens, Calamagrostis epigojos , and Hordeum brevisubulatum) grown in the Hexi Corridor were investigated by Li (1988). The effect of trace elements on the yield of lucerne was determined by Zhang and Zhou (1990), who found that zinc, boron, and cobalt significantly increased yields, whereas no significant effect was observed with manganese, molybdenum, and selenium. Zhang and Li (1990) found that nitrogen and nitrogen-phosphorus had no effect on lucerne yield, whereas phosphorus increased both yield and economic return significantly. Optimal phosphorus fertilization was 55.6 kg per hectare which increased hay production by 2109 kg per hectare. Trace element (selenium, molybdenum) distributions in various grasslands have been studied and their relationship with the associated grasslands established (Ren and Zhou, 1987; Zhou and Ren, 1989; Zhou et al., 1990). According to these studies, the temperate cold grasslands and subtropic damp grasslands are not selenium deficient, but the temperate humid grasslands are severely selenium deficient.

Aerial seeding of forage plants has been reviewed by Huang (1985) and Zhao et al. (1988). Aerial seeding techniques have been intensively studied (Xu and Ge, 1988; Wu and Wang, 1988); 15,000 hectares of deteriorated grasslands in

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