土壤水盐空间变异性指示克立格阈值及其与有关函数的关系

本文以内蒙古河套灌区土壤水盐空间变异性为案例，分析了指示克立格(IK)法阈值与指示概率函数和指示变异函数的关系。探讨了指示阈值的选择原则。认为从提高概率预测精度考虑，水分指示阈值应选择低于中位数的偏小阈值；盐分指示阈值应选择高于中位数的偏大阈值。通过单阈值IK法与普通克立格(OK)法、反距离加权平均法的估计效果比较，发现单阈值IK法可用于具有一定风险条件下的区域性土壤水盐空间插值，该法无需处理特异值，可直接进行估计，估值效果明显优于传统反距离加权平均法，对OK法的平滑效应也有一定改进。

Cutoff value of indicator Kringing method and the relationships between cutoff value and relative functions in expressing spatial variability of soil and salt

The cutoff value of indicator Kringing (IK) method and the relationships between cutoff value and indicator probability function as well as function of indicator variogram for describing the spatial variability of soil and salt in the Hotao irrigation district of Inner Mongolia are analyzed. The principle for selection of cutoff value is investigated. It is found that from the view point of improving the precision of probability prediction, the selected cutoff value of water should be lower, but the selected value of salt should be higher than the intermediate value of data. The comparison among the results of single threshold Kringing value method, ordinary Kringing method and inverse distance weighting (IDW) method shows that the single threshold Kinging value method is suitable to the spatial interpolation of regional water and soil under the condition of specific risk. The method can be used directly and no analysis on outlier is necessary. Its precision of estimation is better than that of traditional IDW method, the mean effect of ordinary Kringing method is also improved.