Geostatistical analysis of soil properties of mid-west Taiwan soils.

摘要

Kriging and cokriging methods were applied to estimate the spatial distribution of soil properties from available large-scale survey data of Taiwan. The data were derived from soils in a 10-km2 area divided into 250 m X 250 m node intervals. The soil properties examined included the extractable P, Ca, Mg, and Fe contents, the sum of exchangeable bases (SEB), %sand, %silt, and %clay. The sum of exchangeable bases and particle-size distribution were regarded as the primary and auxiliary variables, respectively, in the cokriging procedure. The ratio of nugget to total variation was ?7 to 80%, indicating that the spatial correlation of the tested soil properties at the large scale was moderately (cross-)dependent. The estimated spatial distributionsof the soil properties by kriging, under decreasing sampling densities, all correlated significantly (P<0.1%) with those obtained from original data. Furthermore, with the over-sampled particle-size distribution, the overall estimation of SEB quality bycokriging was superior to that by kriging. The results suggested that by kriging and cokriging, the existing sampling density could be decreased under the large-scale sampling interval by nearly half and that sufficient spatial information about the soilproperties could still be retained. The information obtained could be used to improve the long-term sampling designs of soil surveys in Taiwan. It also may be useful for identifying the appropriate sampling densities for these scales of soil surveys.