Spatial Variation Mechanism, Evaluation And Application Of Soil Quality At Different Scales

Through sampling,materials collectiong and field investigation,based on the result of spatial variability of soil fertility factors and heavy metals in rapid industrialization and urbanization areas,this research systematically evaluated soil quality in the study area,and applied it and spatial stability fators to the implementation evaluation and management of basic farmland,high quality prime farmland and cropland requisition-compensation balance; Furthermore,in view of macroscopic soil quality evaluation result not suitable for mountain areas,this study undertook soil fertility quality and its prediction in mountain area.The main objectives were:(1) systematically and globally evaluating soil quality in county(municipal) area by integrating multi-source data for providing the framework of soil quality evaluation in large scale districts;(2) on the basis of the soil quality result,analyzing and revealing changes of soil quality and cropland quality in urbanization to establish the foundation for land planning;(3) aiming at complicated terrain areas,obtaining the spatial prediction method of soil fertility for precision management.The main results,understandings and conclusions of the dissertation were summarized as follows:(1) Basically constructing of the framework of soil quality evaluation of county (municipal) area in fast industrialization and urbanizationFirstly,the research analyzed spatial variability of soil fertility factors and heavy metals, their spatial patterns,soil pollution and pollution sources by geostatistics and mutual information.Secondly,based on spatial distribution of soil quality indicators,the research evaluated soil qualtiy in study area and the mechanism of soil quality affected by industrialization and urbanization through the minimum data set related to geology,soil types and land use.Soil quality indices were divided into four grades according to the classification of region type and fertility of cultivated land in China.Without considering soil environmental factors,the first grade of soil resource accounted for 31.36%of the total area, and mainly located in the northwestern and central region of the study area;The second grade lied at the south and east of the area accounting for 34.34%;The third and fourth grade located in the region from northwest to middle,and accounted for 22.51%and 11.79%, respectively.If considering influence of soi heavy metals,the results showed that soil quality state in every town was the same as previous results and only changed in area.Soil quality index was high for 0.50-0.90 in polluted areas by soil Cd;Soil quality index was higher in combined pollution areas than that in single-factor pollution areas,and its average exceeded 0.78.(2) The method of mutual information combined of decision tree See 5.0 was found for quantitily studying the effect of natural and human factors on soil qualitySoil quality was affected by not only natural factors including parent material,soil type, terrain and etc,but also human activities,especially urbanlization.It was showed that factors affecting soil quality were mainly distance to town,distance to water,altitude,distance to road and distance to industry.In addition,in determining the process of the influence of these factors on soil quality by decision tree,it was suggested that the accuracy based on factors chosen by mutual information was higher than thatbased on all factors.(3) It was suggested that cultivated land quality should be applied to basic farmland, high quality prime farmland and cropland requisition-compensation balance-based on soil quality evaluating result and spatial stability factorsFor basic farmland,the area polluted by soil Cd was 6.22%of total basic farmland area. In soil quality,the first and second soil resources all exceeded 50%of basic farmland,but soil quality of remaining 45%in basic farmland was medium or low,which should be reconstructed.Furthermore,it was showed that more than 80%of the first basic farmland located in the region less than 1km from industry and road.This result suggested that basic farmland near industry are probably replaced by construction land.For high quality prime farmland,the area polluted by soil Cd was 3.69%of the total area. Soil quality of high quality prime farmland dominated by the second and third grade.It was statistically showed that spatial stability risk index was more than 0.80 in 74.24%of high quality prime farmland,the distance of 70%of which to industry and road was less than 1km, and the distance of 30%of which to town less than 2km.The result indicated that high quality prime farmland lying in these regions are easily polluted by soil heavy metal and easily transformed to construction land.For requisited cropland from the year 1996 to 2004,the area polluted by soil Cd was 4.14%of the total area.From view of soil quality,most of requisited cropland from the year 1996 to 2004 belonged to the first grade accounting for 48.05%;But the first grade only had 23.89%in compensated cropland from the year 1996 to 2004.In compensated cropland,the area of spatial stability risk index more than 0.80 accounted for 61.75%,the distance of 28.97%of which to town was in less than 2km,and the distance of more than 60%of which to industry and road was all less than 1km.Compensated cropland in these regions not only were replaced by construction land,but also polluted by industrial waste.(4) Based on tea in Fuyang county,this research chose optimally environmental factors affecting soil fertility quality in tea and the optimal estimation method of soil fertility quality. At last,management zones of tea soil were determined with the map of soil fertility quality interpolated.With topographical factors,NDVI,latitude and longitude as independent variables,this study analyzed and compared different variable selection methods(correlation coefficient method,principal component method,stepwise regression method and mutual information theory) and spatial interpolating methods(stepwise regression,ordinary kriging,co-kriging, regression kriging,generalized neural network and BP neural network ).The result showed that the method of BP neural network combined of mutual information was the best in prediction accuracy,and the factors affecting soil fertility quality in tea plantation mainly included latitude,longitude,altitude and tangential curvature.Scientific and reasonable soil management zoning is the effective means of variable rate fertilization in precision agriculture.Fuzzy c-means clustering algorithm was used to delineate management zones.It was found that through testing of the fuzzy performance index (FPI),classification entropy(MPE) and separate distance(S),optimal clustering exponent and number of classes were 2.0 and 4.0,respctively.To estimate the validity of zoning result, the general statistics analysis on the data was carried out.The zoning statistics showed that soil properties differed sharply between management zones.