TOPSOIL TEXTURE MAPS BASED ON CALIBRATION OF SOIL ELECTRICAL CONDUCTIVITY WITH SOIL DATASETS VARYING IN SIZE

Abstract

The purpose of the study was to verify the possibility of creation of reliable soil texture class (STC) maps of a topsoil based on calibration of shallow (0–30 cm) soil electrical conductivity (ECsh) with small datasets of soil samples with laboratory determined STC. The study was per-formed in three fields located in different regions of Poland: Pomerania (glacial soils), Mazovia (alluvial soils) and Lower Silesia (soils formed from loess-derived sediments over glacial mate-rials). ECsh values were calibrated against four datasets of soil samples. The smallest datasets (5–6 soil samples per field) were selected: 1) in an arbitrary way; or 2) based on the quartiles of ECsh values. A dataset of an intermediate size (11–17 points) and a full dataset of data available (33–38 points) were also tested. The equations used for calibration of ECsh values with fine soil fractions contents were most frequently non-linear. For the fields with smaller ST variation to a depth of 90 cm, such calibration produced STC maps with agreement of more than 90% of area with respective calibration of all data available. The ECsh values depended on the content of fine soil (<2 mm) fractions to a depth of 90 cm, so ECsh measurements can be efficient in mapping the topsoil texture of fields with relatively small texture changes in subsoil. The areas with the same STC obtained using the greatest reference dataset and the smallest dataset are a better indicator of STC assessment quality than the values of assessment errors.