不同尺度网格膜下滴灌土壤水盐的空间变异性分析

进行土壤水盐空间变异性的研究对于膜下滴灌取样设计和抑盐效果的评价有实际参考价值。在新疆玛纳斯县进行了0.5m,5m和50m3个尺度网格田间土壤水盐取样，分别采用经典统计、地质统计及分形理论对土壤水盐的空间变异性进行了分析。传统统计分析表明，3个尺度网格下土壤含水量均具有中等偏弱变异特征且服从正态分布，而土壤含盐量具有中等偏强变异特征且服从对数正态分布。地质统计分析表明，在不同尺度和方向上，土壤含水量和含盐量的半方差函数大多可采用球状模型模拟，其变程随尺度增加而增大，土壤含水量显示出更强的块金效应。采用套合模型可精确描述土壤水盐的总体空间结构。0.5m尺度土壤水盐等值线图沿滴灌带分布，但其它2尺度下此趋势消失。基于半方差函数的土壤含水量和含盐量分形维数(D)在3个尺度和5个方向下有所不同但差异不大，表明土壤水盐性质存在一定范围的自相似结构。分形维数D与半方差函数的参数(基底方差与基台值之比)具有较好的线性关系。

Spatial variability of soil moisture and salt content at different sampling grid scales under plastic mulch drip irrigation

The study on spatial variability of soil moisture and soil salt content is important to sampling design and evaluation of the effectiveness of salinization prevention for under plastic mulch drip irrigation.Field samples were collected at 3 scales of sampling grid (0.5m×0.5m, 5m×5m, 50m× 50m) in Manasi County, Xijiang Autonomous. Spatial variability of soil moisture and soil salt content were analyzed using classical statistics, geostatistics and fractal theory. The result of classical statistics analysis shows that the soil moisture has moderate variability with normal distributions for all 3 scales of sampling grid, and salt content has stronger variability with lognormal distributions. The result of geostatistics analysis indicates that for different scales and directions, most of the semi-variograms of soil moisture and salt content can be simulated by spherical models. The variation ranges of the models increase with the increase of the grid scale, and the distribution of soil moisture exhibits a stronger nugget effect than that of salt content. The whole spatial structures of soil moisture and soil salt content can be accurately described by the nested models. At grid scale 0.5m × 0.5m, the contour maps of soil moisture and salt content distribute along the trickle lines, but no such obvious trend is observed at other two grid scales. The fractal dimensions of soil moisture and salt content obtained from the semi-variogram models in 3 grid scales and 5 directions are slightly different. It implies that a self-similar structure exists at a certain range. A well linear relationship exists between fractal dimension and parameters of semi-variogram.