Spatial Variability of the Granulometric Composition within an Arable Field on Soddy–Podzolic Soil.

The spatial variability of the content of granulometric fraction d > 0.25 mm in the arable layer of soddy–podzolic cultivated soil on an area of 18 hectares was studied. The soil formed on the loesslike loam, underlain by moraine deposits. Samples were taken from the upper (0–10 cm) and lower parts of the arable layer (10–20 cm) following a random-stratified sampling scheme. The total number of samples was 350 cores. The average fraction content was about 22%, the coefficient of variation was 39–41%, and the distributions were approximated by a logarithmically normal distribution. The Spearman correlation coefficient between values at different depths was 0.87. Cartograms of spatial distribution were constructed by the ordinary kriging method using a spherical variogram model. It is shown that preliminary censoring of high sample values (quantile 0.95) yields better results when constructing a cartogram than removing a linear spatial trend and logarithm of the original data. Spatial structures with reduced and increased values were found on the site, the average linear sizes of which was about 100 m. Presumably, they were associated with the heterogeneity of soil-forming material. [ABSTRACT FROM AUTHOR]