Use of an electromagnetic technique to determine sodicity in saline‐sodic soils

Abstract

Soil sodicity is an increasing problem in arid‐land irrigated soils that decreases soil permeability and crop production and increases soil erosion. The first step towards the control of sodic soils is the accurate diagnosis of the severity and spatial extent of the problem. Rapid identification and large‐scale mapping of sodium‐affected land will help to improve sodicity management. We evaluated the effectiveness of electromagnetic induction (EM) measurements in identifying, characterizing and mapping the spatial variability of sodicity in five saline‐sodic agricultural fields in Navarre (Spain). Each field was sampled at three 30‐cm soil depth increments at 10–30 sites for a total of 267 soil samples. The number of Geonics‐EM38 measurements in each field varied between 161 and 558, for a total of 1258 ECa (apparent electrical conductivity) readings. Multiple linear regression models established for each field predicted the average profile ECe (electrical conductivity of the saturation extract) and SAR (sodium adsorption ratio of the saturation extract) from ECa. Despite the lack of a direct causal relationship between ECa and SAR, EM measurements can be satisfactorily used for characterizing the spatial distribution of soil sodicity if ECe and SAR are significantly auto‐correlated. These results provide ancillary support for using EM measurements to indirectly characterize the spatial distribution of saline‐sodic soils. More research is needed to elucidate the usefulness of EM measurements in identifying soil sodicity in a wider range of salt and/or sodium‐affected soils.

Soil Salinity of an Urban Park after Long‐Term Irrigation with Saline Ground Water

“…Nonetheless, the significant positive correlation between EC a and soil properties indicated that an electromagnetic induction survey is an effective technique to capture the geospatial variability in the soil properties. Our findings of a strong correlation between EC e and SAR in soils of arid regions have also been reported by several other authors (Corwin et al, 2003;Amezketa, 2007;Ganjegunte et al, 2014). In areas where salts in the soil are accumulated due to evapo-concentration, EC e and SAR were strongly correlated because of the selective precipitation of Ca minerals in the concentrated soil solution, especially if there are considerable amounts of carbonates.…”

“…In recent years, the EC e Sampling Assessment and Prediction (ESAP) model, developed by the U.S. Department of Agriculture's Salinity Laboratory, is gaining popularity and has been successfully used for delineating the spatial distributions of soil properties from EC a survey data (Lesch, 2006;Ganjegunte and Braun, 2011;Ganjegunte et al, 2013). A strong correlation (e.g., 0.89 in Ganjegunte et al (2013) between EC e and sodium adsorption ratio (SAR) observed in many arid regions indicate that EMI data can also be used to determine spatial distribution of sodicity (Amezketa, 2007).…”

“…The park is divided into 64 irrigation zones and had been irrigated since 1970 with ground water drawn from a low-lying saline aquifer at a rate of 1300 mm yr -1 (Alejandro Tapia, park superintendent, personal communication, 2016). Grab samples of irrigation water were collected at the time of this study and analyzed for pH, salinity, major anions, and cations using the methods described by American Public Health Association (APHA, 2005). The SAR values of water samples were determined using the empirical equation described in Essington (2003).…”

Using Electro‐Magnetic Induction to Determine Soil Salinity and Sodicity in Turf Root Zones

“…A strong correlation between EC e and SAR explained the significant positive relationship between EC a and SAR. Other researchers have also found strong correlations between EC a readings and SAR (Nelson et al, 2002;Corwin and Lesch, 2005b;Corwin et al, 2006;Amezketa, 2007). The coefficients of determination for EC e and SAR were significant; however, due to the sandy loam texture of the soil present in this study, the proportion of the variability explained by the models was not as high as R 2 reported for fine-textured soils (Ganjegunte and Braun, 2011;Ganjegunte et al, 2013).…”

“…Although EC a is generally used for measuring soil salinity, it can also be used to determine spatial distribution of SAR, if there is a strong correlation between EC e and SAR (Amezketa, 2007). Currently, information is lacking whether or not remote sensing EMI technology can be used to track soil salinity in landscape areas that are irrigated with saline water.…”