Electrolytic Conductivity of Semiarid Soils (Southeastern Spain) in Relation to Ion Composition

Abstract

Salt-affected soils are frequent in arid and semiarid regions, where the resulting ill-effects on plant growth and the difficulties for proper soil management make knowledge of the total soil salt content essential. In this study, the relation between the electrolytic conductivity (EC) soil saturation and the 1:1 soil:solution extracts, the salt content, and various saline parameters were analyzed. Ionic characterization data referring to agricultural soils from a semiarid zone (Murcia, southeastern Spain) were used to study the relationship between EC and ion composition. Sixty samples per depth (0–30 cm, 30–60 cm and 60–90 cm) were taken in two years. EC, and Na+, K+, Ca2+, Mg2+, Cl−, NO3 − and SO4 2−concentrations were measured in both extracts. Total dissolved salts (TDS), sodium adsorption ratio (SAR), and total anions and cations were calculated from the relevant data to determine any correspondences among them using Spearman rank correlations. The mean EC values ranged from 0.56 to 0.93 S m−1 and the TDS values from 173 mmolc L−1 to 288 mmolc L−1 in the soil saturation extract and from 0.49 to 0.75 S m−1 and 153 to 233 mmolc L−1, respectively, in the 1:1 soil extract. The correlation coefficient between EC and NO3 −, K+ and Ca2+ (r < 0.70) was lower than between EC and Na+, Mg2+, Cl−, and SO4 2− (r > 0.85) in the saturation extract, in which a strong influence of the ionic ratios (SO4 2−/Cl−, Ca2+/Na+ and Mg2+/Na+) were evident. Increased concentrations of Mg2+, Ca2+ and SO4 2− were not always matched by increases in EC values, suggesting that the measurement of EC in the saturation extract was a good saline content indicator only when the salt content was low, but was less suitable in the presence of high Cl− or Na+ concentrations. The behavior of the ions in the 1:1 soil:solution extract was the same. The best correlation model between the EC values measured in the saturation and 1:1 extracts was a third order polynomial, although good results were obtained with linear and quadratic models.