Topsoil texture maps based on calibration of soil electrical conductivity with soil datasets varying in size

The purpose of the study was to verify the possibility of creation of reliable soil texture class (STC) maps of a topsoil based on a linear calibration of shallow (0-30cm) soil electrical conductivity (ECsh) with small datasets of soil samples with laboratory determined STC . 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 all ST data available (33-38 points) were also tested. For one field, the calibration with ECsh quartiles produced STC maps with greater agreement with field's status than the complete dataset of laboratory results. Although, the root mean square errors and mean absolute errors were greater for quartiles than for the other datasets. The ECsh values depended on the content of fine soil (<2 mm) fractions to a depth of 90 cm, so ECsh measurements are efficient in mapping the topsoil texture of fields with relatively uniform texture in subsoil. The datasets, which produced lower values of errors did not always permit to prepare more accurate STC maps.