Evaluation and analysis of different regression models for estimation of ECe from EC_1:5—With a case study from Buin‐Zahra, Iran*

Abstract

Soil salinity is an important parameter in irrigation, drainage, and environmental studies. Determining the electrical conductivity of soil saturated paste extract (ECe) is a well-known method, but its use is limited because its production process is time-consuming and difficult. The 1:5 solution electrical conductivity (EC 1:5) is an alternative simplified method. The aim of this study was to evaluate ECe-from-EC 1:5 conversion models. A total of 123 samples from 3 soil layers were analysed. The research was planned in two phases: 1) model evaluation in soil layers, 2) model evaluation in ECe categorized data. Results show that the linear model was the best model in the second layer (R 2 = .66, mean absolute percentage error [MAPE] = 0.058), and the exponential model was the best in the other layers (R 2 = .65 to 0.67, MAPE = 0.085 to 0.060). Also, exponential and linear regressions were the best ECe estimation models in the ECe < 4 and ECe > 4 categories, respectively. In addition, the conversion factor (f) for converting ECe and EC 1:5 was obtained as 3.7-13.9, 2.8-5.0, and 3.4-5.8 for three soil layers, respectively. Results show that the use of general recommendation tables for f will lead to considerable error, and the factor must be determined specifically for each region.

Relationships between saturated paste and 1:1 or 1:5 soil/water extract sodium adsorption ratios

“…The above-mentioned results confirm previous research studies about the strong linear relationships of EC e -EC 1:1 and EC e -EC 1:5 for soils from different areas of the world (Aboukila & Norton, 2017;Chi & Wang, 2010;Datta et al, 2019;Hassannia et al, 2020;Kargas et al, 2018;Sonmez et al, 2008;Zhang et al, 2005). However, the slope of the linear relationships appears to be significantly affected by the soil texture, as well as the calcium carbonate and gypsum content for the same method of obtaining the 1:1 and 1:5 extracts and the same range of EC e values.…”

Soil Salinity Type Effects on the Relationship between the Electrical Conductivity and Salt Content for 1:5 Soil-to-Water Extract

“…The influence of salinity on plant growth is mainly based on ECe, so it is necessary to convert EC 1:5 to ECe in order to assess plant response. When there are no available or limited data on soil EC (extract, 1:1, 1:2) and TDS for a given investigated region, then as an initial step or for approximate computation, the obtained relationships from the current study (EC (1:5) = a ×TSS, Table 3) could be used to establish numerous relationships between EC and TDS (or TSS) and between EC and typical salt type from semi-arid and arid regions, for planning of management and irrigation and reclamation strategy [18,20,21,23,27,31,32].…”

“…Many studies assessed the linear relationships between (i) ECe and EC (1:1, 1:2, 1:5); ECe = a × EC + b, (ii) EC and total dissolved salts (TDS, mg L −1 ) concentration: TDS = a × ECe, and (iii) EC and solution ion components (Na + , Ca 2+ , Mg 2+ , HCO 3 − , Cl − , SO 4 2− ): EC = a × Ion (concentration) + b, yet the coefficients and intercepts (a and b) of the linear relationships for the similar studies varied between the regions [2,18,22,23]. The difference between the coefficients was associated along with the soil type, texture, presence of carbonate and gypsum, organic matter content, the method used for extract preparation, and the ratio of exchangeable cations and salinity chemistry [21,[24][25][26][27][28][29][30][31]. Nevertheless, the relationship between EC of various soil/water extract ratios (1:1, 1:2, 1:2.5, 1:5) and particularly the use of EC (1:5) for quantifying soil salinity (TDS) is considered as an alternative simplified method commonly used in many countries [10,23,32].…”

Hydrochemical and radiometric study of groundwaters from serra negra spa, São Paulo State, Brazil

“…Therefore, it has been frequently described in the literature a significant number of correlations between EC and TSD, as well as between EC and concentration of several ions in solution such as Na + , Ca 2+ , Mg 2+ , HCO 3 − , Cl − , and SO 4 2− [13][14][15][16][17][18]. Some of the differences found between the parameters considered have been attributed to soil type, texture, presence of carbonate and gypsum, organic matter content, method used for the sample preparation for analysis, proportion of exchangeable cations, and chemical composition of salinity [18][19][20][21].…”