Spatial distribution of prime farmland based on cultivated land quality comprehensive evaluation at county scale

Abstract: For the cultivated land quality comprehensive evaluation there have been relatively abundant research results at present, but most of them tend to judge the suitability of spatial distribution of cultivated land and prime farmland without taking sufficient attention to the ecological security. The cultivated land quality comprehensive evaluation plays an important part as prerequisites and groundwork in demarcating of prime farmland and high-standard prime farmland construction. On the basis of dissecting the concept and method of cultivated land quality evaluation, the paper constructed a cultivated quality comprehensive evaluation system by way of selecting relevant indicators from the natural quality, site conditions, spatial pattern and ecological security of cultivated land through referring to agricultural land classification, agricultural land gradation, cultivated land scale operation and its ecological security. The study aimed at meeting the inner demands for demarcating of prime farmland and made up for the deficiency in the present related researches, then achieved quantitative analysis of various indexes and calculation on the cultivated land quality comprehensive index with the help of GIS. On the above basis, the study divided 5 916 cultivated land parcels into 4 different types according to the similarity theory in Pinggu district: 1) The first one, named as the prior planning type, was up to 4 325.29 hm2 and accounted for 35.06% of regional total cultivated land area, distributed mainly in the western, southern and southwest plains of Pinggu district, mainly in the town of Donggaocun, followed by the towns of Yukou and Mafang, which showed comprehensive optimum in the natural quality, site conditions, ecological security and spatial pattern of cultivated land as the preferred object to be prime farmland or high-standard prime farmland. This type became the core part of cultivated land protected in Pinggu district. 2) The second one, named as the suitable addition type, was 3511.84 hm2 and accounted for 28.47% of regional total cultivated land area, distributed in the west, south and southwest plains of Pinggu district, especially in the towns of Donggaocun, Mafang and Machangying, which showed a sign of cultivated land landscape fragmentation without any restriction in the other three aspects. This kind of cultivated land's quality comprehensive index decreased mainly due to the spatial fragmentation caused by carving up and occupation from the construction land, which weakened the scale effect of modern agriculture. It was effectual to take action of land consolidation or parcel spatial adjustments to promote the concentration and connectivity for the cultivated land of suitable additional type as the object of the prime farmland or high-standard prime farmland. 3) The third one, named as the main regulation type, was 2 606.45 hm2 and accounted for 21.13% of regional total cultivated land area, whose spatial distribution presented shifting trend from plains to semi-mountainous regions and their restrictive factors were complicated. The changing slope, weakening location advantage and fragmentation were the main reasons for the decrease of some cultivated land's quality comprehensive indices, which could improve the quality to be prime farmland by diversified means such as land leveling project, soil improvement, spatial adjustment of cultivated land parcel and so on. As for the other one that the quality comprehensive index decreased caused by restriction of ecological security pattern, to improve the comprehensive quality was harder than the former one and whether or not to become the prime farmland depended on the coordinated control between the productive and ecological function of cultivated land. 4) The last one, named as the removal quitting type, was 1 892.12 hm2 and accounted for 15.34% of regional total cultivated land area. This kind of cultivated land was not suitable as the prime farmland because of the intense restriction from the natural quality, site conditions, spatial pattern and ecological security of cultivated land. Those ones in mountainous area should bring about the ecological restoration; meanwhile, the other ones in plains should act as the urban greening function with other prime farmlands. The study results reflect the comprehensive quality of regional cultivated land, which have practical and guidance roles in planning method of the county prime farmland protection zone and high-standard prime farmland construction. Simultaneously, the classification of cultivated land can provide a reference for the functional zoning and regulation of cultivated land, the differential construction and management of prime farmland and the transformation of agricultural modernization.