SOIL SALINITY AND SODICITY APPRAISAL BY ELECTROMAGNETIC INDUCTION IN SOILS IRRIGATED TO GROW COTTON
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In the Far West Texas region in the USA, long-term irrigation of fine-textured valley soils with saline Rio Grande River water has led to soil salinity and sodicity problems. Soil salinity [measured by saturated paste electrical conductivity (ECe)] and sodicity [measured by sodium adsorption ratio (SAR)] in the irrigated areas have resulted in poor growing conditions, reduced crop yields, and declining farm profitability. Understanding the spatial distribution of ECe and SAR within the affected areas is necessary for developing management practices. Conventional methods of assessing ECe and SAR distribution at a high spatial resolution are expensive and time consuming. This study evaluated the accuracy of electromagnetic induction (EMI), which measures apparent electrical conductivity (ECa), to delineate ECe and SAR distribution in two cotton fields located in the Hudspeth and El Paso Counties of Texas, USA. Calibration equations for converting ECa into ECe and SAR were derived using the multiple linear regression (MLR) model included in the ECe Sampling Assessment and Prediction program package developed by the US Salinity Laboratory. Correlations between ECa and soil variables (clay content, ECe, SAR) were highly significant (p005). This was further confirmed by significant (p005) MLRs used for estimating ECe and SAR. The ECe and SAR determined by ECa closely matched the measured ECe and SAR values of the study site soils, which ranged from 047 to 987dSm-1 and 227 to 274mmol1/2L-1/2, respectively. High R2 values between estimated and measured soil ECe and SAR values validated the MLR model results. Results of this study indicated that the EMI method can be used for rapid and accurate delineation of salinity and sodicity distribution within the affected area. 2012 John Wiley & Sons, Ltd.
