| Reasonable agricultural land zoning not only to realize efficient land use, but also to promote a healthy circulation of ecosystem and stable social development. Urban areas of Beiing-Tianjin region manifest diversified and complicated agricultural land use resulted from evident topographical and economic location differentiation, which also embrace all the conflicts between development and conservation, economy and environment, and urbanization and food security. As a result, researches on the feasibility of zoning in lessening and solving the conflicts in these areas is worthwhile. Based on the theories like regional differentiation, landscape ecology, industrial structure evolution, sustainable development and agricultural location theory and so forth, this article comprehensively analyzed the relationship between topography and agriculture to illustrate the agricultural land use pattern and traits in each topographical area. Furthermore, agricultural land zoning was conducted in urban areas of Beiing-Tianjin region to designate the dominant function and utility direction of each zone. Finally, countermeasures and proposals were put forward to the implementation of agricultural land zoning rehabilitation mode selection. And the main conclusions are drawn as follows:(1) Topography determines the basic pattern of agricultural land use. With the help of mathematical statistics and spatial analyst extension of ArcGIS, soil property data from typical soil samples in different topographical areas and relevant polygon data were analyzed to uncover the impacts of altitude, slope, soil, hydrology and so forth, on the conditions needed by plant growth, like temperature, farming system, soil fertility, rooting condition, agricultural mechanization, probability of irrigation and salinization, which further outlined the general stand conditions of each geographical area. The natural suitability assessment results of agricultural land indicate that borders of each natural suitability grade and that of geographical areas manifest generalized overlaying. Higher mountainou areas was constrained by the high altitude, steep slope and shallow soil in cultivation condition, there are limited agricultural land use, in which woodland accounts for the dominant part. Low mountain and hill areas own moderate limitation in relief and soil condition,which are agriculturally medium suitable. Alluvial plains show highest agricultural suitability nearly without any natural constraint. Diversified agricultural activities exist in these areas and convert into each other frequently. The salinization in coastal alluvial plain areas abates the suitability, in which farmland and other agricultural land make up the most part. The agricultural land use pattern recognizes the similar distribution trend as topography differentiation.(2) Based on the land use data status quo in2004and2012, traits of agricultural land use changes in different area with different natural suitable level were discussed on the support of ArcGIS and Fragstats software. It can be clearly seen that during the progress of urbanization, high quality farmland reduced sharply by766.35km. However, the enhancement of irrigation and drainage infrastructures promote the increase of medium suitable agricultural land. The amount of medium suitable land was increased by507.60km2from2004to2012. Furthermore, culturable wasteland development added329.06km2more low suitable level agricultural land. Low comparative benefits are the main driving force for the shrinkage and conversion of agricultural lands. From the land use structure, it can be seen that without the natural constraints, high suitable land area manifests highest frequency of agricultural land use conversion. The medium suitable land area shows stable landscape structure; and fewer changes occurred during this period. Low suitable land area indicates marked "belt" characteristics for the limitation of natural conditions. All the analyses set forth above reflect socioeconomic factors also drive agricultural land use presented to the market demand and economic transformation-oriented features.(3) The indicator system of development pressure evaluation was established considering economic location, population and income aspects, under the background of macro-socioeconomy. Further evaluation of development and pressure faced by agricultural land in urban areas was performed. And farmland spatiotemporal changes were discussed. From the results we can see that development and pressure levels reflect donut-shaped distribution. There is positive relationship between the shrinking amount of farmland and development pressure, where the closer to central urban area the bigger development pressure is, and resulting quicker farmland shrinkage, and vice versa. The reasons to the shrinkage of farmland are agricultural structure adjustment and encroachment by urbanization, which recognizes that comparative benefit is the dominant driving force. Newly added farmland is from agricultural adjustment and culturable wasteland development. However, this farmland is of ecological fragility, and culturablly farfetched.(4) Five agricultural zones were divided, taking into account the environmental problems, topography, natural suitability and economic Location conditions. And dominant functions utility direction, rehabilitation modes were put forward accordingly.(5) American land capacity classification and FAO land evaluation are suitable evaluation approaches of traditional agriculture based on natural resource characteristics. However, the improvement of science and technology offset the physical constraints. Land evaluation shall embrace the social and economic conditions around as well, especially in urban areas. Natural condition like altitude and landform is still the basic constraint confronted by modern agriculture.Coupled with the tenet, the partition method of agricultural land based on the natural suitability evaluation and economic location superimposed development pressure assessment, it was suggested that arrang basic farm land between Beijing and Tianjing as urban growth boundary, plant grain crops surrounding the two central cities, and develop the facility agriculture such as greenhouse in the coastal plain saline. This land use layout might be the best choice of developing modern agriculture in metropolitan region. |
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