Using electrical conductivity data (EC_a) in soil survey is popular because it is related to several soil properties and is less expensive to collect than numerous soil samples. Theoretically sound reasons exist to explain such relationships but they vary spatially making interpretation of EC_a data difficult and some have looked at relationships for which there is no basis in theory. McBratney et al. (2005) suggested that relationships developed between high frequency devices like time-domain reflectometers can be used to inform interpretation of the lower frequency EC_a data and presented a three part theory, where, depending on certain conditions EC_a is measuring salinity, soil depth or variations in clay and moisture content.

Soil data and EC_a measurements from several fields were used to determine whether this model provides insights into the causes of variations in EC_a. The conditions met in each field were determined and geostatistically mapped. Moving correlations were used to determine the relationship between EC_a and soil properties around each data point. Results suggest that EC_a can indicate variation in different soil properties depending on location in a field but surveyors need to be able to know what EC_a is measuring without collecting numerous soil samples. Is this possible?

Reference

McBratney, A. B., Minasny, B. & Whelan, B. M. (2005) Obtaining ‘useful' high-resolution soil data from proximally-sensed electrical conductivity/resistivity (PSEC/R) surveys. In: J. V. Stafford ed. Precision Agriculture '05. p. 503-511. Wageningen Academic Publishers, Wageningen, Netherlands.