Multiple linear modelling of electrical conductivity at a subsurface drainage site in Haryana using EM technique

Abstract

Electromagnetic measurements (EM) have proved its usefulness in the investigation of the soil salinity that provides electrical conductivity (EC) values using an EM probe in both horizontal and vertical modes quickly. Such measurements are useful for assessing the impact and management of farm practices on soils and crops. However, the values of EC measured by the EM probe do not always match to that of the true values of electrical conductivity of saturation paste extract (ECe) and also it varies with the moisture content of soil. The present study was conducted to model the salinity of a subsurface drainage project installed in Rohtak district of Haryana using the apparent electrical conductivity (ECa) values provided by the EM probe (EM38). The soil samples collected at 0-15, 15-30, 30-60 and 60-90 cm depths were analyzed to determine the ECe, electrical conductivity of 1:2 soil solution (EC2), pH of saturated paste (pHs), pH of 1:2 soil solution (pH2), HCO3-, CO3--, Cl-, Ca++ + Mg++, Na+, K+ and the Sodium Adsorption Ratio (SAR). The observed values obtained by the EM38 for apparent electrical conductivity (horizontal) [ECa (H)] and apparent electrical conductivity (vertical) [ECa(V)] were modelled using linear and multiple linear regression (MLR) for determining ECe as dependent parameter. The modelled values of the ECe were correlated with the observed values. The coefficient of determination (R2) varied from 0.7 to 0.95 for the MLR model fitted among the ECa(H), ECa(V) and ECe. The MLR was also fitted along with the observed soil moisture content, ECa(H) and ECa(V). MLR model with soil moisture content was found to be better (R2=0.71 to 0.99) predictor of ECe with combination of ECa(H), ECa(V). The estimated ECe at different depths were mapped in the form of iso-haline contours using Surfer software which described the spatial distribution of soil salinity in the area and may help in quick selection of management and cultural practices.