基于方差四叉树法的滨海盐土电导率采样布局研究

利用土壤空间变异特性和空间分布特征进行采样设计是当前土壤采样研究的重要内容。采用方差四叉树法（Variance quad-tree method，简称VQT），结合半方差函数，设计滨海盐土采样的最优布局。并利用普通克立格法对传统网格采样法与方差四叉树采样法所得到的不同的样点数目进行插值，计算估值误差并进行精度比较。结果发现，同样的样本数目，利用方差四叉树法得到的克立格估值误差明显地较利用网格采样法得到的克立格估值误差小，其采样效率提高约16％一25％。该方法的优势在于，可设计在土壤特性变异大的区域密集采样而在变异较小的区域稀疏地采样，从而在有效表达土壤空间变异性的同时，提高了采样效率，减少了采样成本。

SPATIAL SAMPLING SCHEME FOR COASTAL SALINE SOIL BASED ON THE VARIANCE QUAD-TREE (VQT) METHOD

Sampling designing based on spatial distribution and variability of soil properties is an important issue in recent studies on soil sampling.In the present study,the variance quad-tree method(VQT),combined with the semivariogram function,was used to design an optimal sampling scheme in a field of coastal saline soils.The ordinary kriging method was adopted to interpolate the sampling points fixed with the regular grid method and the VQT method,respectively,and their prediction errors were subsequently calculated for accuracy comparison. Results reveal that with the same size of samples,the VQT sampling scheme was much smaller than the grid one in prediction error,and hence its sampling efficiency was improved by 16% to 25%.The advantage of the VQT method is that this scheme samples sparsely in fields relatively even in soil properties and more intensively in fields varying sharply.Thus it not only characterizes variability within the sampling area,but also improves sampling efficiency,and hence saves sampling cost.