GEOSTATISTICAL ANALYSIS OF SOIL PROPERTIES OF MID-WEST TAIWAN SOILS

Analysis and interpretation of soil survey data are very important for effective management of agricultural fields. In this study, kriging a nd 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-km(2) area divided into 250 m x 250 m node intervals. The soil properties examined included the ext ractable P, Ca, Mg, and Fe contents, the sum of exchangeable bases (SE E), %sand, %silt, and %clay. The sum of exchangeable bases and particl e-size distribution were regarded as the primary and auxiliary variabl es, respectively, in the cokriging procedure. The ratio of nugget to t otal variation was about 57 to 80%, indicating that the spatial correl ation of the tested soil properties at the large scale was moderately (cross-)dependent. The estimated spatial distributions of the soil pro perties by kriging, under decreasing sampling densities, all correlate d significantly (P < 0.1%) with those obtained from original data. Fur thermore, with the over-sampled particle-size distribution, the overal l estimation of SEE quality by cokriging was superior to that by krigi ng. The results suggested that by kriging and cokriging, the existing sampling density could be decreased under the large-scale sampling int erval by nearly half and that sufficient spatial information about the soil properties could still be retained. The information obtained cou ld be used to improve the long-term sampling designs of soil surveys i n Taiwan. It also may be useful for identifying the appropriate sampli ng densities for these scales of soil surveys.