| Soil plays a crucial role in the terrestrial ecosystem which is supported by the following statements. On the one hand, soil provides nutrients for animals’ and plants’ growth; on the other hand, soil is the place where waste in the atmosphere and hydrosphere is filtered and circulated; on the third hand, soil is the largest terrestrial carbon stock. As we all know, soil quality is the combination of fertility quality, environment quality and health quality. Since its crucial role, study in the variation of soil quality can help understand global environmental change and currently is the core of contemporary soil science.As sustainable development accepted universally, the world pays more attention to agriculture and food security. Considering that farmland, the carrier of agriculture, is decreasing in quantity and degrading in quality, which is caused by industrialization, urbanization and natural disaster, unreasonable human activity, it is very necessary to conduct deep study in farmland soil quality. The basic function of farmland soil is production, that is the ability of providing nutrients for crops, so we place particular emphasis on fertility quality of farmland soil quality.Yixing County, located in the developed Yangtze River Delta region, south of Jiangsu Province, has excellent location and convenient transportation. The north of the county, river plain region, is one of the important bases for commodity grain production in Taihu Lake region; the southwestern county is generally in the part of Tianmu Mountain; east is close to Taihu Lake. So the county has diverse landform types. Spatial characteristics of soil quality in Yixing were studied in this article. The purpose was to master the variation and causes of soil quality, so as to give suggestions to exploit farmland reasonably, efficiently and sustainably.There were three aspects of this study, as showed following:firstly, by methods of traditional statistics and geostatistics, soil quality indicators were classified and evaluated, and their spatial variation were analyzed; secondly, by method of fuzzy mathematics, soil comprehensive quality was evaluated; thirdly, by certain models of quantitative geography, spatial distribution of soil quality was analyzed. The results are as follows:(1)Farmland soil elements of Yixing County were abundant in OM and N, but were lacking in P and K; for medium-trace elements, except Mo, all were sufficient; Ca and Se were asymmetrically distributed relatively.(2)Results of geostatistics showed that, variation characteristics of all indicators were different in every direction; every indicator presented spatial autocorrelation to some extent. Nugget/Sill of Na was0.2362, which referred to strong spatial correlation; others presented medium spatial correlation, and their spatial variability was caused by structural and random factors, containing local micro-climate, geological background, soil parent material, industrial and agricultural activities, and so on.(3)Through approved Principle Component Analysis (PCA), five indicators were chosen to construct the Minimum Data Set (MDS). These five indicators explained74.7%of all variance. In this article, we found that Fuzzy Mathematics could be well applied in the evaluation of farmland soil quality. In the end, Soil Quality Index (SQI) was calculated by model of weighted sum, and the SQI was classified into five grades. The evaluation showed that, farmland soil fertility was in high quality, shown in details as the ratio of first and second grade reached28.64%and the third grade reached50.88%. These results were in accordance with the abundant single indicators.(4)Based on the comprehensive evaluation, with the method of quantitative geographical models, spatial pattern of farmland soil quality was analyzed. It was showed that, soil in river plain for farmland in the north and in cluster of farmland in the west was in high quality, so in these two regions, high-quality farmland should be protected; soil in hills and mountains region in southwest and cluster of construction land in the middle was in low quality, so in these two regions, low-quality farmland should be prevented from further deteriorating.(5)In the end, reasons causing spatial variability of soil quality were discussed. It was proposed that, combination of landform factors and soil types factors was the basic reason for variability; on the other hand, human factors, such as land use and land planning made the variability more complicated. In the end, for the purpose of capital farmland construction, suggestions were proposed for the utilization of land resources in both zones of capital farmland and non-capital farmland. |
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