| Mu Us sandland, a very important ecological barrier and a representative region of coupling development between farming and stockbreeding, locates in the Farming-Pastoral ecotones of north China. Because it locates in forest-grass-desert juncture area, and be affected by the low vegetation coverage, the loose land surface composition, the susceptible human disturbance, and so on, its ecosystem shows the strong frangibility, sensitivity and instability, so the human unreasonable production and management activities easily cause ecological environment degradation rapidly. Thus, it has very important theoretical value and practical significance to research the agroecosystem of Mu Us sandland. This paper, in the 50 years time scale, at the regional, county and indoor domain spatial scale, specially selects Yuyang district in farming-dominant zones and Wushen banner in grazing-dominant zones of Mu Us sandland for the comparative study object, at the same time, uses the study methods of combining regional investigation and field verification, combining qualitative analysis and quantitative study, combining dynamic evaluation and static analysis and combining induction and deduction, and deeply studys the coupling principle and mechanism, coupling environment, coupling effects, harmonious development status in Mu Us sandland coupling agroecosystem, etc, moreover, puts forward the optimization model system and sustainable development mechanism of coupling agroecosystem. The main conclusions of this study are as follows:(1)Before human economic and social activities, through water resource distribution and availability, the grassland, oasis and desert in Mu Us sandland interacted, and then formed a natural coupling ecosystem. The systemic disturbances, agricultural social and economic activities at foundation of human exploitation and utilization natural resources, speeded exchange and circulation of energy flow, material flow and information flow among every agricultural subsystem, consequently, its agriculture and husbandry system, agricultural products processing industry system and outside systems realized coupling. At the same time, on the condition of breaking administrative separatist, ideal coupling pattern of Mu Us sandland agroecosystem is a semienclosed zone spectrum of system coupling, there is a main city group, such as Taole, Yinchuan, Yongning, Lingwu, Yanchi, Dingbian, Jingbian, Hengshan, Yuyang, Shenmu, Fugu, etc. the city group plays a extremely important role of radiating dirve.(2)During near 50 years, the climate of Mu Us sandland tends to more warm and humid gradually, because it has the relative matching light-temperature-water in year, at the time of rationally developing summer crops, this place should develop the planting of artificial grass, accordingly, the advantage of centralized climatic resources in summer and autumn can be used adequately. Though research, we found 6 counties of Mu Us sandland southeastern margin are all highly suitable regions, Shenmu is the best one and Dingbian is the worst one; all of counties possesses abundant heat and sunlight quantity, but all short of precipitation, Dingbian lacks precipitation badly; the evaluation result of climatic function is Shenmu>Fugu>Jingbian>Yuyang=Hengshan>Dingbian, totally, the higher climatic function in the northeast and the lower climatic function in southwest of Mu Us sandland. Precipitation is the uppermost restrained factor on exertion of the climatic function of pasture stockbreeding system.(3)The serious contradiction of relationship between human and land is the internal origin, decisive factor and direct driving force of desertification in Mu Us sandland, despite of looking from time and spatial view, the desertification is in the reversed stage wholly. We found, in the desertification natural and social factors, that farmland area, evaporation capacity and strong wind days can cause stronger influence on desertification in Yuyang district than in Wushen banner, the agricultural population, livestock amount and precipitation can cause stonger influence on desertification in Wushen banner than in Yuyang district, and agricultural population is the largest desertification factor in this two counties; the combined force of human desertification factors increases continuously, moreover, desertification contribution ratio of human factors is larger in Wushen banner than in Yuyang district, so the human factors is the main force that cause desertification in this two counties; the comprehensive effect of desertification factors banner is more serious in Wushen than in Yuyang district, on a long view, the driving force and the possibility of desertification development are all stronger and higher in Wushen banner than in Yuyang district.(4)The structural characteristics of regional soil water is the basic factor about landscape formation in Mu Us sandland. From the view of field landscape, evaporations during a day and a year in barefield is much more than in cropfield, the evaporation in barefield is affected by dry sand layer and only shows change of single-peak curve; the acute change layer of soil water content exists in cropfield during corp growth period, furthermore, water amount in barefield is better than in cropfield; seepage amount of field water is about 141.25mm, maize transpiration is about 175.3mm, potato transpiration is also about 183.91mm, moreover, the evapotranspiration or the water-consumption of corps in field of maize and potato is about 306.48mm and 303.29mm respectively. From the view of agricultural industrial structure, in Yuyang district, farming is the dominant industry, stockbreeding is the most potential industry, so well dealing with relationship between farming and stockbreeding, properly controling scale, emphasizing the development of herbivorous animal husbandry and reasonably decreasing grain-consumption pig husbandry are very important; in Wushen banner, stockbreeding is the mainstay industry of national economy development, farming and stockbreeding are both in the developing stage, so strengthening the improvement and optimization of animal variety, enhancing the transformation and utilization ratio of forage grass and feed and appropriately developing special livestock breeding will play a very important role; forestry and fishery still have larger development space.(5)Because of the impact on land use change causing by great ecological engineering, the ecosystem service value shows as follows, in Yuyang district, that woodland and grassland are the main components of total value, the values of various land use type manifest the two stage characteristics of rapid change period and slow change period; the total value and the value of woodland, garden land and traffic land all show the evolvement from rapid increase to slow increase along time, and the value of farmland, grassland and idle land show the evolvement from rapid decrease to slow decrease along time; the total ecosystem service value increases about 0.19×109 RMB, the increasing value of unit area land is about 254 RMB; the counties in increase on ecosystem service value mostly distribute in southeast and north, and the counties in decrease on ecosystem service value mostly distribute in middle and west of Yuyang district, furthermore, the distribution of total value and unit area value in every village show the characteristic of large in northern part of the Great Wall and small in southern part of the Great Wall.(6)During near 27 years, grain production in primary production occupies a decisive function in Yuyang district, grass production in primary production is the uppermost part in Wushen banner, all these expressly explain what is the farming-dominant and grazing-dominant model of farming-stockbreeding coupling development; food-consuming animals culture, such as pigs, poultry, will be the dominant industry in Yuyang district, and herbivore livestock production will be the dominant industry in Wushen banner; agricultural and animal husbandry production system in Yuyang district is more open than in Wushen banner, so in Yuyang district, its energy flow, material flow and information flow with outer systems'exchange frequently, system control intensity is also stronger, accordingly, system output is also higher; the emergy transformity between farming and stockbreeding district is higher in Yuyang, additionally, more reasonable animal variety structure in stockbreeding, more rapid replacement and update speed of animal variety, all of above bring the higher system coupling degree, however, the development potential of farming-stockbreeding coupling is enormous in Wushen banner.(7)As the most basic production unit, eco-economy systems of farming and grazing households are of significance to the implementation and outcome of national policies. The eco-economy systems of farming and grazing households were studied by emergy theory and emergy analysis methods. The emergy input and output structure of different industrial models in Wushen banner and Yuyang district have been compared and analyzed, the result shows us that the input of nonrenewable industrial subsidiary energy occupies a leading position in farming-dominant zones, but the input of renewable organic energy occupies a leading position in grazing-dominant zones of Mu Us sandland. The total characteristics of pattern and development of typical eco-economy systems of farming and grazing households are described and compared quantitatively by net emergy output ratio, emergy investment ratio, environmental loading ability, emergy power density, productivity of unit acreage, emergy cost per capita, emergy possession per capita, system production priority, system stability index and sustainability index. the study could help to provide strategies for development and optimization of farming and grazing household industrial models in farming-dominant zones and grazing-dominant zones of Mu Us sandland.(8)According to theory of harmonious development, the models of development degree, carrying capacity, harmonious development degree and integrated determinant criterion are established, and then, are used in Yuyang district in farming-dominant zones and Wushen banner in grazing-dominant zones of Mu Us sandland. Results show:①the development degree, carrying capacity and harmonious development degree in these two regions have increased during near 27years;②the types of harmonious development between SE and REn also have gone to higher levels gradually;③the structures of agricultural industry have changed from resources-intensive industry, whose development mainly relys on consuming resources and environment, to technology-intensive industry, whose development mainly depends on using capital and technology, inchmeal;④due to influences of intensity on mankind activities and openness in agroecosystem, the carrying capacity and development degree of SEREn system in Yuyang district and Wushen banner have happened evolutional characteristics along time sequence, and status of harmonious development between SE and REn also have had changes correspondingly. Therefore, the earlier development of agroecosystem with samller population in Mu Us sandland farthest depended on the cost of consuming the carrying capacity of REn, the fragile entironment, restricted resource and laggard SE badly confined the building of harmonious development of SEREn system, besides, the development model of saving the carrying capacity of REn was confronted with restrictions, such as technology, capital and market. After the middle of 90s, with the construction of entironment and the optimization of agricultural economic structure, the satisfactory situation appeared in SEREn system gradually, the harmonious development of REn and SE have evolved into higher level step by step. Through integrated determination on status of harmonious development between SE and REn, we want to find the key factors, which can synchronously meet the demand on development of SE and conditions of REn in a certain period, at the same time, the exploitation and utilization of resources and environment can accelerate the development of society and economy, conversely, the development of society and economy can provide more supports on protection and restoration of resources and environment. We hope our study could help to provide references on method and theory for building resource-saving, environment-friendly agricultural SE system, and impeling the harmonious development of SE and REn to go higher levels.(9)Optimization models of agricultural ecosystem has played an important role in smooth running of fragile agriculture ecosystem. Based on an analysis of the environmental background and systematic limitation of Mu Us sandland in the northern part of China, a new point of view was proposed in this paper for the model optimization of sandland coupling agroecosystem. Namely, the industrial structure has to be modified so as to make a functional integration of different parts of the whole system, according to the theories of ecological recovery, ecological engineering, the high efficient utilization of resource and complementary industry, and to design the ecology structure of defense, the planting structure of saving water, the pasturage structure of stabilization and industrial structure of benefit when to pay attention to functional availability of agricultural ecosystem, which is feasible on condition that reasonably dealing with the relationships of agriculture and stockbreeding, forestry, energy-industry, and so on. It is important that ecosystem models can be harmonized, integrated and coupled efficiently. We are looking forward to giving academic gist and technical support at model optimization for similar coupling agroecosystem in the adversity.
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