A comparison of salinity measurement methods based on soil saturated pastes

Abstract

Soil salinization is of great concern in the irrigated arid and semi-arid western U.S. due to its threat to sustainable agricultural productivity and thus is closely monitored. The measurement of electrical conductivity in saturated paste extracts (ECe) is the standard to which other salinity estimation methods are referenced. Since this method is laborious, the preparation of saturated pastes subject to bias, and salinity estimates by electrical conductivity (EC) subject to chemical artifact, numerous other methods have been proposed. These include EC measurements in diluted saturated paste extracts (ECed), direct measurement of EC in soil pastes (“Bureau of Soils Cup” method, ECcup), and EC based on electromagnetic induction (ECH25ECe). The main objective of this paper is to compare these four saturated paste-related methods of estimating salinity with respect to specific soil management goals. Comparison of the methods across six soil depths and three textural groups demonstrates that estimates of salinity are significantly influenced by the method, depth of sampling, and soil texture. Whereas ECe and ECcup estimates differed significantly from each other and from those of the other methods, ECH25ECe and ECed estimates were similar. In addition, high correlations between estimates of salinity by ECH25ECe and ECe indicate their similarity and suggest the suitability of the ECH25ECe method as a reference parameter for monitoring salinity. Thus, the suitability of the ECH25ECe method is drawn from its similarity to 1) the superior ECed method, which corrects for salinity underestimation due to ion pair formation, and 2) the ECe method, which is the standard method against which other salinity estimates are traditionally compared. This finding was consistent across all depths, the three texture groups, and the combinations of method and depth or texture groups. The high coefficient of variation in ECe and ECcup highlights the subjectivity of these methods and raises questions about the choice of ECe as standard for salinity estimates. These results therefore suggest that the ECH25ECe method (which requires few collocated but representative ECe measurements) be used to rapidly and reliably monitor salinity in calcareous soils of arid and semiarid regions.