单种复合类型单元土壤全量元素空间变异的幅度效应

Scale Effect on Spatial Variability of Soil Total Elements in Single Complex Type Unit of Land Use-Soil Type

土壤属性变异性的幅度效应研究对土壤数字制图、土壤调查及农业生产均具有重要意义。针对江西东乡县研究区域水田—中潴灰鳝泥田(土种)一种土地利用与土壤的复合类型单元,设定了8个土壤采样幅度研究区,并利用多层次嵌套布点方法在每个采样幅度区分别布设60个采样点,共采集337个样点的土壤表层(0~20cm)样品;运用多种函数拟合分析手段,揭示单种复合类型单元(水田—中潴灰鳝泥田)土壤全氮、全磷、全钾含量的空间变异性随采样幅度的变化特征。结果表明,土壤全量元素的空间变异性均具有明显的幅度效应特征,全氮、全磷、全钾含量的变异系数均随采样幅度的拓展而逐渐增加,而增加趋势则逐渐变缓。不同土壤全量元素空间变异性体现出不同的幅度效应特征,土壤全氮、全磷变异系数(%)的幅度效应刻画函数为CV=b×Da(R2>0.87,p<0.001),土壤全钾为CV=e(a/D+b)(R2>0.93,p<0.001),D为幅度表征指标(km);不同土壤全量元素变异系数随采样幅度快速与缓慢变化的幅度分界点位置存在明显差异,表明基于复合类型单元的土壤多属性调查采样布点与分析策略需要统筹考虑。研究结果对于红壤丘陵区县域土壤调查样点合理布设具有重要的启示和参考价值。

[Objective] Effects of sampling scale on spatial variabilit significance to soil digital mappings, soil survey, and agricultural production. y of soil properties are of great So, in this study, a tract of the grey eel-mud field （Soil Species ） , a special land use--soil type complex unit （Lu-SoTy） , in Dongxiang County, Jiangxi Province, a hilly red soil region in South China was selected as an object. Using the multi- level nesting sampling protocol to ensure that the total number of soil sampling points remains unchanged whatever sampling scale is used, the study is to exposit characteristics of spatial variability of soil total element concentrations with soil sampling scale and provide important implications and scientific references for rationalizing layout of sampling points based on Lu-SoTy. [ Method] In the light of spatial distribution of soil sampling points, eight soil sampling scales （ from the smallest to the largest is coded in turn as A1 - A8 ） were designed with smaller scales located inside larger ones. By taking into full account vastitude and uniformity of spatial distribution of the sampling points, each soil sampling scale had 60 points distributed evenly. Using the multi-level nesting sampling protocol, 337 sampling points were laid out across the County. In December 2014 after the crop .of late rice was harvested, soil samples were collected from the 0 - 20 em topsoil layer at all the sampling points for analysis of soil total element concentrations. Scale characterization indices were calculated using ArcGIS 10.2.2, variability characterization indices using SPSS 20.0, and regression fitting analysis of scale characterization indices and variability characterization indices, using SPSS 20.0. Based on the level of significance and RE of the regression, the best characterization indices and the best fitting functions were screened out. [ Result] Results show that the scale effects on spatial variation of soil total elements are obvious; and coefficients of variation （ CV ） of TN, TP and TK go up with expansion of the sampling scale, but the increasing rates display a decreasing trend; the scale effects on the spatial variability differed with soil total element： the best fitting function for charactering the scale effects onCV （%） isCV =bxDaforTN andTP （Rz〉0.87, p〈0.001） , andCV =e（-D＋b） （R2〉 0.93, p 〈 0.001 ） for TK （D is a scale index of sampling points; namely： average distance to the nearest one point or maximum distance （ km ） of all the sampling points ） ; the shifting points of scale effects between rapid and slow changes of CV varied with soil total element, for example, the shifting point of TN, TP and TK is Do = 6.756 km, Do = 9.061 km and Do = 3.408 km, respectively （at this point, the angle between the tangent to the curve and the horizontal axis is about 30°） . All the findings demonstrate that independent sampling protocols and analysis skills need to be considered in studying spatial distribution of different soil total elements. [ Conclusion ] The scale effects characteristic of spatial variability of soil total elements in soil of a special complex Land Use-Soil Type unit, could provide important implications and scientific references for laying sampling points at county scale soil surveys in hilly red soil regions.