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[Estimation on value of water and soil conservation of agricultural ecosystems in Xi' an metropolitan, Northwest China].

With the urban eco-environment increasingly deteriorating, the ecosystem services provided by modern urban agriculture are exceedingly significant to maintain and build more suitable environment in a city. Taking Xi' an metropolitan as the study area, based on remote sensing data, DEM data and the economic and social statistics data, the water and soil conservation service of the agricultural ecosystems was valued employing the remote sensing and geographic information system method, covering the reduction values on land waste, soil fertility loss and sediment loss from 2000 to 2011, and analyzed its changes in time and space. The results showed that during the study period, the total value of water and soil conservation service provided by agricultural systems in Xi' an metropolitan was increased by 46,086 and 33.008 billion yuan respectively from period of 2000 to 2005 and from 2005 to 2011. The cultivated land (including grains, vegetables and other farming land), forest (including orchard) and grassland provided higher value on the water and soil conservation service than waters and other land use. Ecosystem service value of water and soil conserva- tion provided by agriculture was gradually decreasing from the southern to the northern in Xi' an metropolitan. There were significantly positive relationship between the ecosystem service value and the vegetation coverage. Forest, orchard and grassland distributed intensively in the southern which had higher vegetation coverage than in northern where covered by more cultivated land, sparse forest and scattered orchard. There were significantly negative correlation between the urbanization level and the value of water and soil conservation. The higher level of urbanization, the lower value there was from built-up area to suburban and to countryside within Xi' an metropolitan.