| Cultivated land is an important resource to support the development of social economy.It guarantees the security of ecological and food for human beings and builds the foundation and lifeline for the development and modernization construction of agriculture.The scientific evaluation of the quality for cultivated land is the prerequisite for the double management.Also it is great valuable for the Government's scientific decision-making to master the changes of the spatial-temporal pattern of cultivated land.Nancheng County is well-known with the reputation of "Gan-Fu granary".In this paper,we take Jiangxi province Nancheng County as the research area.We do the research mainly from three points such as the land productivity,the land fertility,the sustainable development and so on.Then construct the appraisal model based on the genetic algorithm(GA)and support vector machine(SVM).Finally the cultivated land quality in Nancheng County from year 2012 to 2016 is evaluated on the basis of GIS spatial analysis techniques.This paper discusses the changes of cultivated land quality and the characteristics of spatial differentiation from the changes in the quality of the detached arable land,the changes quality of arable land,and the concentration of arable land,in order to build foundations for government planning and decision-making.The key works and conclusions were listed as following:(1)Thirteen factors such as the natural conditions,the landscape patterns and the area conditions are selected as the evaluation indicators.Support vector machine(SVM)and genetic algorithm(GA)are applied to construct a farmland quality assessment model named GA-SVM.(2)The GA-SVM model is used to evaluate the cultivated land quality and the study area is divided into five grades ranging from grade one to five.In 2012,the arable land area was 18516.24 hectares,5333.06 hectares,184.18 hectares,511.56 hectares and 558.76 hectares;in 2016,the other five arable lands were 18417.02 hectares,5327.71 hectares,211.87 hectares,566.96 hectares and 599.49 hectares.(3)From 2012 to 2016,Grade of cultivated land overall decline 0.01.the arable land loss in the irrigated arable land was mainly concentrated in urban area of Nancheng County.It mainly reflects on the reduction of high-quality arable land,and the most of new arable land were poor.For the county-level changes in the cultivated land quality,the shift of mass center is mainly based on the fourth and fifth grades,among which the geocentric shift distance for fourth is 2513 m,and fifth is 2511 m.In terms of spatial changes for the land quality in townships,the shifts range from high to low are: 5176 m for the fourth grade in Rita town,4542 m for the fifth grade in Longhu Town,2687 m in the third grade in Xujia Township,1117 m for the second grade in Xujiaxiang Township and 823 m for the first grade in Suixi Township.(4)During the period from 2012 to 2016,the space Gini coefficient for Nancheng County was increased with a trend of aggregation for the fourth grade.On the contrary,the other grades were not.After further global and local autocorrelation analysis,the index of Nancheng County was increased year by year;the LL type of Nancheng County has increased from 12 in year 2012 to 13 in 2016,and the HH model increased from 7 in year 2012 to 9 in 2016. |
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