Gansu and Qinghai
Wan Changgui and Tian Shuning
SURVEYS, STANDARDS, AND CLASSIFICATION SCHEMES
During the past two decades, several grassland surveys have been conducted in Gansu and Qinghai provinces (Map 1-4) (Qinghai Grassland Extension Service, 1977; Zhou and Li, 1981; Hu and Mu, 1982; Zhou et al., 1987). Some of these studies, including the surveying and mapping of the alpine grassland of southern Gansu and Tianzhu County by Ma et al. (1984a,b), have made use of remote sensing. A large-scale grassland survey organized by the Gansu Grassland Ecological Research Institute (GGERI) and using remote sensing was carried out in the grasslands of the Qinghai-Tibet Plateau in the late 1980s. This survey, which covered an area of more than 400,000 km2 of remote rangeland, ranks as one of China's outstanding scientific achievements.
Based on data gathered in Gansu, Ren et al. (1965, 1980) have proposed a new grassland classification system called ''integrated orderly grassland classification.'' In this system, the first order of classification, "class," is determined by a combination of two factors, water and temperature. The second order, "subclass," based on characteristics of soil and topography, can serve as an indicator of land use. The third order, "type," is defined by a relatively
Dr. Wan Changgui, former research associate at the Gansu Grassland Ecological Research Institute, and Tian Shuning, Ph.D. candidate at Texas Tech University, survey grassland research in Gansu and Qinghai provinces. Work in these two provinces has included attempts to establish standards and classification schemes, basic research on productivity and nutrient cycling, and applications such as reclaiming salinized soils, improving forage and feed, controlling pests, and developing grassland agricultural systems.
homogeneous vegetation cover. Grasslands of the same type should have similar feed value and be treated with similar range management practices. Finally, the "subtype" is distinguished by the presence of one dominant plant species and a characteristic variety of subdominants.
Ren's classification system is based on the proposition that zonal grassland distribution is affected primarily by bioclimatic conditions, namely, heat and moisture. Therefore, grasslands can be identified by an index that represents a combination of these two factors. Ren et al. (1965) define the quantity of heat as the annual accumulated temperature above zero (Σø) and propose eight grades of heat quantity from frigid (Σø < 1100) to tropical (Σø > 8000). Their moisture index is K, where K = r/0.1*Σø and r is annual precipitation in millimeters, yielding six grades of moisture from extremely arid (K < 0.28) to damp (K > 1.82). By using this classification system, the world's grasslands can be divided into 48 classes, 38 of which have been identified in China and 27 studied in Gansu Province (Hu et al., 1978). Using annual precipitation (r) as the abscissa and annual accumulated temperature (Σø) as the ordinate, Ren and colleagues (1980) have developed a key chart that indicates the "classes" of China's grasslands. Given the annual precipitation and annual accumulated temperature, any grassland can be assigned a location on this chart. For example, the Yongfeng grassland in Tianzhu County has Σø = 1331°C and r = 441 mm, placing it in zone 42 on the chart, a "cold-temperate, humid" grassland, or alpine meadow.
This key chart shows fundamental soil and vegetation characteristics and can be used to estimate the primary biomass of grasslands (Ren, unpublished data, 1980). It also facilitates the study of relationships between classes and prediction of how the development of a particular grassland might be affected by climatic change. Ren's classification system has been used to study animal distribution and ecology, and ecological amplitudes of Xinjiang merino and Tan sheep have been located on the key chart (Xia, 1983; Hu et al., 1984).
Lu et al. (1984) compared Ren's moisture index with Bailey's moisture model and Holdrige's potential evapotranspiration ratio and found that they are highly correlated and simple to compute. An application of these three models in Gansu Province has produced similar results and shown that they can be used to classify natural landscapes. Using the moisture index, Ren et al. (1984) divided the arid regions of northwest China into three categories: semiarid, arid, and superarid, based on K values of 0.85–1.18, 0.28–0.83, and <0.28, respectively.
Using fuzzy mathematical expression, Ge and Chen (1984) derived a binary index for each grassland. These indices reflect the water-temperature features for range sites and describe the sites in the fuzzy spectrum of rangeland ecosystems. Thus, the typical characteristics of each "class" and the relationship between the "classes" can be determined quantitatively and calculated easily. Fuzzy mathematical expression has made Ren's classification system more applicable.
In this and other areas, Ren Jizhou has sought to establish new standards or modes of analysis that will lead to better rangeland management. In a 1978 study, for example, Ren and colleagues analyzed the grassland production process and proposed a program of seasonal animal husbandry. In this work, the authors divided the energy flow of grassland production into six stages: solar energy to plant biomass, plant biomass to available forage, available forage to forage intake, forage intake to digestible nutrients, digestible nutrients to animal biomass, and animal biomass to available animal productivity. They calculated energy conversion efficiency at each stage and concluded that available animal productivity can vary from 0 to 16% of net primary productivity. To maximize animal productivity, the energy conversion efficiency must be increased at each stage, particularly the last. As an alternative to established livestock practices, Ren et al. (1978) proposed a new method based on the seasonal availability of forage. In this method, herders should: (1) increase the number of reproductive females in the flock; (2) fully utilize the forage in summer pastures by herds made up of greater numbers of newborn and young animals, which should be sold in early winter to reduce the requirements for winter forage or stored feed; and (3) cull less productive (old and weak) animals to alleviate grazing pressure in winter and to reduce weight loss and death in the rest of the flock. In 1979, experiments at GGERI's Tianzhu grassland research station realized a fourfold increase in animal productivity by using this system (Anonymous, 1979a). Recently, the system has been adopted by state ranches and individual herdsmen in many parts of China (Li, 1990a).
Again, Ren and others (1980) challenged the existing practice of measuring productivity of the grasslands in terms of number of animals, which in their view had led to overstocking and overgrazing, by proposing a different standard—namely, the Animal Product Unit (APU): 1 APU is equivalent to a 1-kg gain of body weight of grazing beef cattle under moderate conditions. That represents 26.5 therms of digestible energy, 22.5 therms of metabolic energy, and 13.9 therms growth in net energy. The number of APUs of other animal products can be obtained by calculating the energy required to produce them. Using similar methods, Hu (1979) calculated the APU values of various animal products. Ren and his colleagues warned that unless some new standard replaced the current reliance on animal numbers, overstocking would increase, while the grasslands and the quality of livestock that depend on them would continue to deteriorate. Recently, the APU has been accepted as the official standard and is now listed in China's Dictionary of Standards.
GRASSLAND AGRICULTURAL SYSTEM
In the early 1980s, GGERI's Qingyang [County] Loess Plateau Experimental Station (QLPES) launched a project to develop a Grassland Agricultural System, whose purpose was to repair the damage caused by the reclamation of
land and the extension of agriculture in this region. This system used grasses and legumes as the key elements in soil conservation and rehabilitation, and sought to improve efficiency by combining agriculture and animal husbandry into an agroecosystem (Ren, 1985). More than 50 researchers in six disciplines from different institutions, including the Gansu Institute of Social Sciences, have taken part in the project. Results of this research include papers on loess plateau farming systems; the introduction and evaluation of forage grasses; nitrogen fixation characteristics of legumes; agricultural economics; ruminant nutrition; plant pathology; plant community ecology; and surveys of forage resources, human behavior, rodents, and insects (Gao et al., 1987).
In 1982, the year the QLPES Grassland Agricultural System was established, the area planted in grain decreased by 17%, the area of legume plants such as alfalfa and sainfoin was expanded 167%, and improved breeds of ruminants were introduced and their numbers increased. Four years later, solar energy use efficiency had increased by 33% to nearly twice the local average. The content of organic matter, nitrogen, and phosphorus in the soil increased by 22.6, 6.2, and 102%, respectively. Production increases per unit area were 62% for protein, 58% for energy, and 60% for grain. Total production increases were 37% for grain, 62% for grain stalk, and 178% for forage. Although a severe natural disaster occurred in 1985, the average grain yield per unit area was 3.3 times higher than the local average. Total agricultural output doubled in four years, while the share occupied by animal husbandry increased from 15.9 to 56.8%, and land use efficiency increased 168% (Ren and Ge, 1987). Ge and Gao (1985) have shown that between 1982 and 1984, the share of total agricultural output occupied by animal husbandry increased from 15.9 to 47.2%.
Lu Shengli et al. (1987) reported on an investigation of 24 households that participated in the QLPES Grassland Agricultural System experiments. They found that as a result of the increase in area sown in alfalfa, solar energy use efficiency increased 29.4%, and the amount of nitrogen fixed was 13 kg per mu (15 mu equals 1 hectare), which was two to three times the nitrogen removed from the soil by non-nitrogen fixing crops. Consequently, grain production per unit area increased 184% from 1982 to 1984, which was 47% above the national average. Soil runoff from grasslands (12 degree slope) was equivalent to 26% of runoff from cropland (2 degree) and to 4.4% of runoff from bare hillsides (9 degree). Owing to the application of more animal manure, greater nitrogen fixation by legume crops, and the reduction of soil erosion, soil organic matter increased 23%. With the development of animal husbandry, annual income per household increased 56% in two years, and the proportion of income from animal products reached 42.3%. The average income of 58 families in one village, Xiazui, exceeded by 50% the average household income in Gansu as a whole. Increases in animal production also contributed to the development of small-scale industries, such as food and fur processing.
The Grassland Agricultural System developed at GGERI's Jingtai [County] Experimental Station produced similar results. He and Ge (1990) have shown that in this case, when corn was intercropped with beans and sweet clover, the production of grain, crude protein, and energy—and the economy as a whole—increased significantly in comparison to areas devoted to monoculture. In addition, the occurrence of crop diseases was drastically reduced (Ge Wenhua, personal communication).
As described by Ren and Shen (1990), the Grassland Agricultural System has four production levels: preprimary production (recreation, soil conservation); primary production (crops, forage, medicinal herbs); secondary production (animals and animal products); and postsecondary production (processing and commodity circulation). Organized in this way, the agrosystem can operate more efficiently, while causing less environmental damage. Forage plants play a key role in this system by preventing soil erosion and enriching the soil. Agricultural by-products, which represent 75% of the plant matter not directly consumed by people, can be converted to animal products. Animal manure is used to improve soil fertility. Unlike traditional agriculture in which the farming season ends with the last harvest, in the Grassland Agricultural System, forage production begins before planting and continues after the harvest.
RECLAMATION OF SALINIZED LANDS
Establishment of the Grassland Agricultural System has been accompanied by reclamation of salinized agricultural lands, which can be reseeded in grass. In the past, reclamation of saline land relied on an engineering approach, which has been found to be too expensive. With the help of Wu Qingnian of the Jilin Academy of Agricultural Sciences, a group of researchers introduced to the Hexi Corridor several salt-tolerant perennial species of the genus Puccinellia, most notably P. chinampoensis.
Several years of field trials have shown that Puccinellia is well adapted in slightly to medium-saline soil and can survive in heavily saline soil in some circumstances. The salt dynamics of the saline land and the ecophysiology of Puccinellia and other salt-tolerant species (Phragmites communis, Agropyron cristatum, Achnatherum splendens, Calamagrostis epigojos, and Hordeum brevisubulatum) have been studied and the results reported in a special issue of Pratacultural Science of China (1988). The findings of this project include the following: (1) Under field conditions, Puccinellia can tolerate a salinity of 2.4% in a 45-or 60-cm soil profile. (2) Puccinellia seedlings are less tolerant of high salt content; therefore irrigation must be applied at an early growing stage. (3) Puccinellia can desalinize salt-affected land in two to three years, bringing salinity down from 2–3% to 0.2–0.4% in a 30-cm soil profile. (4) After the establishment of Puccinellia, there is little seasonal or annual fluctuation of soil salinity (Zhu et al., 1988). (5) Three years after Puccinellia was established,
various crops (wheat, barley, alfalfa, sugar beets, and corn) were planted on the previously saline land (Zhu et al., 1988), and production of these crops reached the local averages. (6) Puccinellia is a valuable forage crop with an average production of 3–7.5 tons (air dry) per hectare (Mao et al., 1988).
The mechanism by which Puccinellia desalinizes the soil is not well understood. Some evidence suggests that Puccinellia canopy can reduce evaporation, allowing less salt to accumulate in the upper soil profile (Wan and Zou, 1990a). Others point out that Puccinellia sward can improve soil structure and the water penetration rate, favoring the salt-leaching process (Yan et al., 1990). When grown on salt-affected soils, Puccinellia also tends to concentrate soluble sugar in the leaf tissue, lowering the plant water potential and facilitating the movement of water from the soil to the plant (Wan and Zou, 1990b). The objective of the saline land reclamation program is to establish artificial Puccinellia pastures in the Hexi Corridor. In the future, young animals will be brought to the valley from the mountain grassland to be fattened on the spring and summer growth of these pastures.
PRODUCTIVITY AND NUTRIENT CYCLING
There have been several reports on the primary productivity and biomass of alpine grasslands in Gansu, and Qinghai provinces (Yang et al., 1981; Hu and Mu, 1982; Lang et al., 1984; Zhou and Zhang 1986; Hu et al. 1988a,b, 1989; Wang et al., 1988a; Yang, 1988; Xia, 1988). Growth patterns, phenological and physiological characteristics of forage species have also been studied (Shi et al., 1988; Wang et al., 1988b; Zhang Shuyuan et al., 1988). The Kobresia meadow in Qinghai has a primary productivity (190–340 g/m2 dry matter per year), similar to that of alpine grasslands in Gansu (Yang et al., 1981; Hu et al., 1988a). According to Hu et al. (1989), when Kobresia meadow is fenced and irrigated, its primary productivity can be doubled; if the meadow is further plowed to grow oats (Avena sativa) and bromegrass (Bromus inermis), a fivefold increase in forage productivity can be realized. In the meantime, root/shoot ratios show a steady decline from the native Kobresia meadow to the hay pastures, suggesting that the establishment of artificial hay pastures may help solve the problem of shortage of winter feed.
The nitrogen circulation pattern and animal production in alpine grassland ecosystems have been studied by Wang (1982), Ren (1984), Meng (1988), Wang Zuwang (1988), and Fu et al. (1989). These studies show that heavy losses of energy and nitrogen usually occur in winter, leading to animal weight loss of up to 25% (Anonymous, 1979b). The current level of hay supplement is barely enough to avoid starvation. Optimum stocking rates and carrying capacities in the Qinghai alpine grasslands have been studied by Zhou et al. (1986) and Shen (1985). Research on energy metabolism of ruminants has been carried out by Pi (1981) and Zhao and Pi (1986). Forage intake of
grazing sheep has been studied by Liu (1979), Zhu and Wang (1980), and Pi (1981).
PESTS AND PATHOLOGY
Rodent community and control research has been conducted in a wide range of grassland ecosystems (Song and Liu, 1984; Song et al., 1984). Cheng (1987) investigated rodent population distribution in eastern Gansu and found that the average density was 5.6 per hectare for 27 species. Song and Liu (1984) found 11 species of rodents in the Hexi Corridor; Meriones unguiculatus had the largest population. The rodent population in the desert grassland was 2.5 times greater than in the farmland. Kong et al. (1990) successfully controlled Ochotona curzoniae and Meriones unguiculatus by setting up stands to attract birds of prey, such as Buteo hemilasius and Felco cherrug . Their research has shown that 75% of food intake by the birds was rodents. The area controlled has been as large as 33,000 hectares, with considerable economic returns and great advantages over chemical control. Liang (1982) evaluated the population density changes of plateau pika and common Chinese zokor (Myospalax baileyi) after the application of chemical controls, and found that the density of the pika would return to pretreatment levels in one year. The relationship between the density of plateau zokor and the severity of damage to the vegetation of the Haibei alpine meadow was systematically studied by Liu et al. (1982) and Fan et al. (1989). Zhong et al. (1986) investigated the influence of heavy snow on the population density of the plateau zokor, plateau pika, and root vole in Haibei alpine meadow. The energy requirements during pregnancy and lactation in the root vole (Microtus oeconomus) were studied by Wang et al. (1982).
Insect pest problems in Gansu Province were reported by Feng (1989) and Lu Ting (1984a, 1987). From 1972 to 1988, Feng collected 25,000 insect samples and identified 367 species. He and his coworkers also investigated spider population dynamics in forage crop fields (Feng and Ma, 1988; Feng and Li, 1989). Lu Ting (1984b) studied the alpine relationships between the locust population and different compositions of vegetation. Lu Ting et al. (1987a) found that the average density of locusts was 8/m2 in the southern Gansu grasslands and could reach 30/m2 in some years. In Xiahe County of Gansu Province, 20,000 hectares of grasslands were infected with locust each year. Aerial application of chemicals to heavily infected grasslands has been a common management practice in these areas. Various pest control techniques have been reported by Lu and Cao (1986) and Lu et al. (1986). Lu Ting et al. (1987b) have compared mixed pastures to monocultures and shown that in the former the quantity of dominant species in the insect pest community (especially ground pests) is much lower and the quantity of preying insects higher. The population of insect pollinator species was largest in alfalfa-sainfoin fields.
Forage pathology studies have focused on major diseases and fungi infecting alfalfa and other forage species (Liu, 1984; Liu and Hou, 1984; Nan 1985, 1986; Hou et al., 1984; Liu and Nan, 1987). Liu and Hou (1984) reported more than 100 fungal diseases infecting the legume family in northern China. Liu and Nan (1983) studied major forage diseases in the Hexi Corridor. The Peronospora aestivalis disease of Trigonella ruthenica was intensively studied by Liu (1976, 1978, 1989). Nan (1990) investigated the fungal diseases of cultivated grasses and forage legumes in the loess plateau of eastern Gansu, and evaluated disease resistance of various forage varieties. He also studied Uromyces striatus disease of Medicago sativa (Nan, 1987a); the effect of Uromyces orobi on the growth and nutritive value of Vicia sativa (Nan, 1987b); and Erysiphe folygoni, a disease of Melilotus officinalis, in Qingyang (Nan, 1987c). Nan (1986a,b) demonstrated that the occurrence of Pseudopeziza medicaginis and U. striatus of alfalfa was reduced 27.7–76.2%, and Botrytis fabae and Stemphylium botryosum of sainfoin 18–85% in mixed as compared to monocultural pastures.
Based on results achieved with the Grassland Agricultural System, efforts have been made to build optimization models for the Hexi Corridor. Using IBM modeling, Jiang (1988) suggested that population control combined with the proper integration of desert, oasis, and mountain grasslands could transform the corridor into a base for grain and meat production. Zhang and Ge (1990) developed an optimization model for the agrosystem in the desert-oasis grassland of Jingtai County, which emphasized the importance of small ruminants. An optimization model for the Linze County agrosystem is currently being developed.
Other modelers have followed a different path. Ai and Gu (1984) and Gu et al. (1984) have used models of agroclimatic suitability analysis to study bioclimatic zonation of the Gansu loess plateau and concluded that most of the investigated areas belong to the steppe or arid steppe. They pointed out the significance of grass planting in protecting the fragile ecosystems from further deterioration. Using the Integrated Rate Methodology (IRM) modeling of farming ecosystems, Li (1987) showed that as the proportion of grasslands in the rolling hills and slopeland of the loess plateau increases, grain production per capita will show a slight decline in the first five years but will increase thereafter. When the grassland area reaches 50% of total agricultural land, per capita energy production will be much greater than under any other pattern of land use.
Ecological modeling has aroused great interest among Chinese scientists in recent years. Chen et al. (1981) built mathematical models for the retrogression of populations of three steppe species (Stipa breviflora, Agropyron cristatum, and Artemisia frigida) under grazing conditions in Gansu. Liu et al. (1986)
studied the interaction between wild rye (Elymus nutans) and the plateau pika (Ochotona curzoniae, Hodgson) in the Haibei alpine meadow station in Qinghai using simulation models. Quantitative studies of vegetation succession on the abandoned arable land of the subalpine meadows in southern Gansu have been carried out by researchers from the ecology lab of Lanzhou University. These include analysis of community compositions (Zhang Dayong et al., 1988), classification and ordination (Du and Wang, 1990), and succession of the artificial grassland (Zhang, 1990). Two of these papers were published in one of the leading journals in this field, Ecological Modeling (Zhang, 1988, 1989).
System dynamics and systems analysis have become popular tools in agroecosystem studies. Yang and Hardiman (1987) developed an interesting bioeconomic model of the farming system in the southern tableland of the Oingyang loess plateau. A simulation model of animal population dynamics and herd structure in the southern Gansu grasslands was developed by Lu and Song (1988). The model attempted to predict the future animal population and the impact of these animals on the grasslands of that region. Lu Shengli et al. (1987) used linear programming to analyze the Qingyang County loess grassland agroecosystem. The same method was employed by Cui et al. (1988) to optimize the structure of livestock in Jingtai County, Gansu, and by Li and Nie (1984) to evaluate the grazing system of that province. Lu et al. (1990) also developed a dynamic model for a grassland agroecosystem.
Since 1988, GGERI and Colorado State University have undertaken cooperative research on ecological modeling of the alpine grazing system. The simulation model devised in this project accurately predicts aboveground primary production of various vegetation types in the Yongfeng grassland of Gansu and agrees with the current understanding of factors controlling plant production in that system (Swift et al., unpublished results, 1990). A linear programming model of the Yongfeng grassland has also been developed (Bartlett et al., unpublished results, 1990) and refined to determine critical factors in the production of sheep and yak. In the future, this model will be used to ascertain possible solutions to limiting factors. Through such collaboration, Chinese scientists have learned to apply simulation modeling and linear programming to grazing systems, and are extending these techniques to study other Chinese grassland ecosystems.
FORAGE AND FEED
Forage study focuses on the introduction, improvement, and nutritive value of forage crops. Lucerne and sainfoin are the major legume species in the Gansu loess plateau region. There were 226,700 hectares of lucerne (Medicago sativa, M. falcata, M. media) in Gansu Province in 1983, which was 23.7% of the lucerne planted throughout China (Wu and Zhang, 1988a). In 1988, the acreage of sainfoin (Onobrychis sativa) was more than 20,000 hectares. From
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
Gansu had been seeded aerially by 1981 (Zhao et al., 1988). Forage production normally increased 2 to 10 times in the seeded areas, whereas surface runoff and soil erosion were reduced by 56 and 97%, respectively, by two-year-old Astragalus adsurgens pasture established aerially (Liang et al., 1987). Soil organic matter more than doubled, five years after A. Adsurgens was seeded (Li, 1990b).
Some new concepts and theories have been introduced by younger Chinese scientists. Fuzzy mathematic theory has been applied to study the retrogressive succession stages of the Stipa steppe in southern Gansu (Zhao et al., 1982) and to evaluate the function of grassland farming ecosystems (Li et al., 1984). Grey system analysis was used by Duan and Li (1990) to study the Grassland Agricultural Systems of Gansu.
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