Harmonization of the Results of Soil Salinity Chemical Study

Abstract

Soil salinization is one of the main environmental factors that limits the growth and productivity of many plants. Soil salinity is assessed by different methods in various countries of the world: by the method of water extracts in Russia and a number of other countries and by electrical conductivity of extracts from soil pastes all over the world. These methods are time consuming, thus short-cut methods are used for mass analysis. For example, the salt status of soils is often assessed by the leading toxic ion (chlorine or sodium) in Russia or by electrical conductivity for different soil to water ratios (1 : 1, 1 : 2.5, 1 : 5, and 1 : 10) in a number of other countries. In this work, we compare different methods to substantiate the use of electrical conductivity measured in a suspension 1 : 5. The following approaches are analyzed: 1—determination of the specific electrical conductivity in water suspension (1 : 5); 2—measurement of pNa and pCl in water suspension (1 : 5) by ion-selective electrodes; and 3—determination of sodium in water extract (1 : 5) by atomic absorption spectrometry. Salinization is evaluated in samples of light clay soils of the dry steppe zone mainly of chloride-sodium salinity. The results show the strongest correlation between measurements of the specific electrical conductivity (by conductometer) and sodium activity (by ion-selective electrodes). A rather close relationship between the specific electrical conductivity and the content of sodium ions in water extract has been revealed, and a conversion function of these parameters has been obtained: ЕС_1 : 5 = 0.213Na_1 : 5 + 0.17 (with a free term) and ЕС_1 : 5 = 0.23Na_1 : 5 (without a free term). It is proposed to use the following criteria to assess the salinity by electrical conductivity (dS/m) in water suspension (1 : 5): 0–0.4, nonsaline; 0.4–0.6, slightly saline; 0.6–1, medium saline; 1–1.9, strongly saline; and >1.9, very strongly saline. The comparison of different gradations of soil salinity by cross tables, using the chi-square test and the Kappa index, shows statistically significant correlation, which enables the use of various analytical methods to assess soil salinity.