| Baicheng lies in the northwestern part of Jilin Province, west of Nenjiang plain and it is located in the confluence of Horqin grassland and the great plain of Songliao. It concludes Taobei district, Taonan city, Da'an city, Tongyu county and Zhenlai county, and it is an important grain and animal husbandry base of Jilin Province.Baicheng Prefecture has prominent regional advantages, convenient traffic and abundant land resources. It belong to the temperate continental monsoon climate, and the light and heat conditions is superior. Its water area is broad, and water resource is suitable to develop agriculture. Agricultural irrigation source of water of Baicheng Prefecture is mainly groundwater, and the sources of area which is close to surface are rivers and bogs.There are a lot of problems in the agricultural production of Baicheng Prefecture. The regional natural calamity is comparatively frequent, and natural calamity such as drought, waterlogging, wind, frost and hail often occurs in this area. By the way, the drought among them is primary natural calamity of this area. In addition, because of historical reason, cultivating and herding excessively for a long time, the phenomenon such as the farmland invade and occupy the grassland, sand blown by the wind invade and occupy the farmland, grassland degradation, land desertification, soil salinization and alkalization and land degradation become severe increasingly. It result in that the physical and chemical properties of soil become bad, the organic content of tilth soil drops, and the agricultural ecosystem is destroyed seriously. The environmental pollution arising from population growth and industrial development also brings certain influence to agricultural production.Taking into account the status above, we account the service value of agricultural ecosystem and assess ecosystem health, which can find out existing problems of agricultural ecosystem, and understand fundamentally, assess scientifically, controll rationally and utilize continuously the service value of agricultural ecosystem, and offer the theoretical foundation for the scientific management of agricultural ecosystem and the ecological security study of farmland. It will make the agricultural ecosystem offer greater utility for human existence and sustainable development.I adopt in Baicheng Prefecture's statistical data, assay data and Landsat7 satellite TM image data (1989,2000,2004) which are interpreted by our group, and take market value assessment method, substitution engineering method, shade price method and substitute economics method and opportunity cost method, etc.. Aiming at agricultural ecosystem of Baicheng Prefecture, I accout the function values of products, climate regulating, water resource conservation, nutrients circulation and environment depuration, then calculate the total service value of Baicheng Prefecture.By calculation, in Baicheng Prefecture, the service value of agricultural ecosystem service in 1989, 2000 and 2004 are respectively 993,080,000 yuan, 1,889,860,000 yuan and 2,405,180,000 yuan, which had increased by 1.42% during 1989-2004. Among 15 years, the service value of the agricultural ecosystem rised gradually. The value of service of products and environment depuration showed a tendency to rise, and the function of water resource conservation had rised slightly, and the regulating function of gas had rised after reducing. The function value of material circulation presented the downward trend year by year, which was reduced to 117,570,000 yuan in 2004 from 150,800,000 yuan in 1989, and reduced by 22.04%. The considerable growth of the service value of products explains the increase of the agricultural output, which relates to the increase of farmland area for over ten years, but the unit area of agricultural output in Baicheng Prefecture is dropping. The value of nutrients circulation represents the ability that the tilth soil offer nutrient for crops to a certain extent, and its reduction explains the decline of soil fertility. Because wind erosion and the man-made estrepement and uncontrolled grazing, the physical and chemical properties of soil become bad, and the content of soil nutrients drops.During 1989-2004, the proportion of the service value of non-products to the total value had dropped from 60.89% to 25%. It was obvious that people ignored the environmental service function of the agricultural ecosystem while increased grain yields blindly. So, we should also pay more attention to the indirect value of the agricultural ecosystem.The author set up an index system of agricultural ecosystem assessment, it concludes water, soil, economy and society, biology and climate sub-systems. I use the analytic hierarchy process (AHP ) for the determination of weighting coefficient, and the multi - level fuzzy comprehensive evaluation to evaluate health level. The result indicates that the health level in Baicheng degraded in general. The degradation of agricultural ecosystem health level is related to the increase of saline land and soil land, the degradation of the soil quality and the mode of cultivation.Among the county-level cities and counties in Baicheng Area, the ecosystem health of Taobei is the best, In 1989, the health level isâ…¡, in 2000, it degraded toâ…¢, and it lasted to 2004. the ecosystem health in Daan is the worst, it degraded toâ…¤fromâ…£. The ecosystem health level in Taonan degraded toâ…£fromâ…¢. The level in Zhenlai isâ…£between 1989 and 2000, and it recovers toâ…¢in 2004.According to the results of service function and the health of the agricultural ecosystem, In allusion to the questions of Baicheng Area, I have proposed adjusting the agricultural structure, intercropping, crop rotation, water conservation, Improving the efficiency of water utilization, develop new water resourse, returning farmland to forest or grassland. In conclusion, comprehensive administration of the agricultural ecological environment of this district, we must arrange for the proportion of agriculture, forestry and animal husbandry appropriately, adjust the agricultural production structure, strengthen the management of grassland, resume grassland ecosystems, control the population growth rate, improve the quality of environment protection consciousness of the residents. Only in this way can the agricultural ecosystem of Baicheng develop better and more rapidly. |
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