Calibration of Electromagnetic Induction Device (EM38) for Soil Salinity Assessment

Electromagnetic induction tools are extensively applied worldwide for rapid evaluation of spatial variability in soil salinity. This study was conducted in pistachio orchards of Chah Afzal area of Yazd Province for assessment of soil salinity using electromagnetic induction (EM38) device in two plots of 45 and 40 ha with clay loam soils and average moisture contents of 25 and 35 percents, respectively. A systematic sampling grid with the size of 20×80m was established. At each grid point two EM38 readings were taken in horizontal (EMh) and vertical (EMv) orientations. Different calibration equations were employed for conversion of the readings to electrical conductivity of the saturation paste and the best method was selected. Results of this study showed that the best calibration method was multiple linear regression equations fitted to the field data. It was also found that more reliable regression equations could be derived at 35% moisture content in comparison with 25% moisture content between soil salinity at different depths of soil and horizontal/vertical readings, with correlation coefficients (R2) of 0.67 to 0.85, respectively. Consequently, soil salinity maps of different depth intervals and also soil salinity profile maps at upstream and downstream of the field borders were generated and interpreted.