The physical and chemical properties of a soil depend largely on its mineralogical constitution. Even over short horizontal distances, spatial variability may be high, and are best described by classical descriptive statistics associated with geostatistics. The objective of this study was to characterize the spatial variability of clay mineralogical properties of soils from the Guabirotuba formation, in the metropolitan region of Curitiba (PR), by classical descriptive statistics (especially coefficient of variation - CV) and geostatistics to propose more adequate sampling standards for these soils. The B horizon samples were collected at the intersection of a georeferenced grid at regular intervals of 30 m, plus 10 % additional randomly located points to reduce the nugget effect (135 total samples). For the description of dispersion and variability of the data analysis classical descriptive statistics was used (mean, median, maximum, minimum, standard deviation, coefficient of variation, skewness, kurtosis and Shapiro-Wilk test) and to characterize spatial variability geostatistics were used to establish semivariograms. The CV of the kaolinite contents was low (10.8 %), but spatial variability was high, with a reach of only 22.4 m. The property with the highest CV was the ratio amorphous Fe/crystalline Fe (94.6 %), indicating a wide dispersion of the values in relation to the mean but its reach was 64.6 m, indicating medium to low spatial variability. A pure nugget effect was only observed for isomorphic Fe substitution by Al in hematite. Crystalline Fe was the property with the highest reach, with a value of 625 m. However, when analyzing the contents of hematite and goethite separately, the spatial variability was wider.
Geostatistics; kaolinite; gibbsite; goethite; hematite
