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Spatial Variability Analysis of Some Soil Properties Using Geostatistical Techniques
Thesis Abstract:
Geostatistical techniques, specifically the semivariogram and kriging, were applied to characterize the spacial variability of soil properties.
Data on percent sand, percent silt, perecent clay, percennt organic matter, ppm potassium (K), and ppm phosphorus (P) from soil samples collected by regular grid sampling schemes, which converts about 9,000 hectares or sugarland in Negros Occidental, was used in this study.
For each soil property, a semivariogram was calculated. A spherical model equation was found fitted to each semivariogram and the parametric coefficients of the equation were identified as nugget variance, sill, and range.
The structure of the semivariograms revealed a strong degree of spatial dependency of the measured soiI properties. However, ppm K and ppm P tended to ahve value of nugget variance approaclnng the value silt. This indicated the tendency of these properties to vary consideranly at shorter distances. A sampling distance of 300 meters was optimal.
The fitted spherical model equation of each semivariogram was used in the kriging process or in interpolating unknown values of kriged values. A kriged value is a weighted moving average value of known neighborhood values. The precision of the kriged value was tested by a self-validation technique known as "jackknifing."
Jackkniffing showed insignificant differences between kriged and measured values of the same point using t-test at five percent level, indicating that the kriged values were optimal. Using the measured and kriged values, contour maps for percent organic matter, percent sand, percent silt, percent clay, and ppm K of the topsoil were drawn.
