| Urban Agriculture (UA) must be Sustainable, and Ecological Agriculture (EA) should be become the development direction of UA, which is the common understanding now. UA should strengthen study on direction, resource utilization, leading industry, and evaluation indicators system. On those things this article starts.The main characteristic of UA is its high intensive on input, so it has produced serious pollution to environment. In water use: the ratio for agriculture of Beijing UA was high, mostly of ground water, resulted in underground tundishes and water pollution. The virtual water contained in the agricultural products in 2003 of Beijing was 8.779 billion m3, mostly of creatural products; There would be 227.4 billion m3 virtual water to reach the well-to-do standard. On land resource: Nowadays, with the decreasing of agricultural land, the dosage of fertilizers is increasing, the fertility and yields are improved together with the pollution. The correlation coefficient of total N between 0-20cm and 20-50 on soil section has reached 0.9703. The demand for ecological footprint of Beijing in 2003 was 2.30507, but the ecological carrying capacity only reached 0.26715. Those things have threatened the sustainable development.Owing to its special position, the leading industry of UA is different from general agriculture, and so can not be made at will. It was blindness of Beijing to make vegetable & stockbreeding as the UA support industries without any consideration of the water using and the possible serious non-point pollution especially.About the case study, Shunyi district is the representation of developed agriculture region in Beijing suburb. The nutrition of almost all the land using types is assembling now using the model NUTMON. Miyun district is the lagging representation whose economic development has conflicts with environment protection. The unwanted nitrogen in the year 2003 was 2891 t and redundant phosphorus was 384 t. The definition of Ecological Capital (EC) was given. The total value of EC of Miyun (forestry, water and air were concluded) now is 10.741 billion RMB yuan. In the analysis of Green GDP of Miyun district, the decreasing and deterioration of environment from 2001 to 2003 accounted for 0.01%-1.78% of GDP.On the research of UA's function, the approach to develop EA was brought forward for Beijing UA, but one new form - SEEA-the Ecological Agriculture to use agricultural Substances circularly (including agricultural trash), to use Energy contained in the agricultural substances fully. On the theory of comparative and competitive advantage, the leading industry of Beijing EA was made, i.e. the industry collection on agricultural products production, processing, transport and service of organic horticulture (vegetable, fruits, flower) and stockbreeding (sheep, dairy, poultry, cattle and other stockbreeding) with top grade and Biomass Utilization. And a new form of SEEA named "hand-in-hand agriculture" was advanced by the author, which involves ten different forms, i.e., pet agriculture, game agriculture, drift agriculture, and virtual agriculture, and so on.The sustainable development of UA should need inspection and evaluation. A new UA Sustainability Indicators System was constructed, including 13 indicators on ecosystem undegradable, economically viable, and socially acceptable, the exponential function was engaged to resolve the subjective prefer in establishment of indicator weight, and the total calculation and analysis method were also proposed. And another new indicators system-IESIS (Inf-Exergy Sustainability Indicators System Framework) -to inspect the status of the sustainability of social development was also designed.
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