Estimation of soil salinity in a drip irrigation system by using joint inversion of multicoil electromagnetic induction measurements

Low frequency electromagnetic induction (EMI) is becoming a useful tool for soil characterization due to its fast measurement capability and sensitivity to soil moisture and salinity. In this research, a new EMI system (the CMD mini-Explorer) is used for subsurface characterization of soil salinity in a drip irrigation system via a joint inversion approach of multiconfiguration EMI measurements. EMI measurements were conducted across a farm where Acacia trees are irrigated with brackish water. In situ measurements of vertical bulk electrical conductivity (sigma(b)) were recorded in different pits along one of the transects to calibrate the EMI measurements and to compare with the modeled electrical conductivity (sigma) obtained by the joint inversion of multiconfiguration EMI measurements. Estimates of sigma were then converted into the universal standard of soil salinity measurement (i. e., electrical conductivity of a saturated soil paste extract - ECe). Soil apparent electrical conductivity (ECa) was repeatedly measured with the CMD mini-Explorer to investigate the temperature stability of the new system at a fixed location, where the ambient air temperature increased from 26 degrees C to 46 degrees C. Results indicate that the new EMI system is very stable in high temperature environments, especially above 40 degrees C, where most other approaches give unstable measurements. In addition, the distribution pattern of soil salinity is well estimated quantitatively by the joint inversion of multicomponent EMI measurements. The approach of joint inversion of EMI measurements allows for the quantitative mapping of the soil salinity distribution pattern and can be utilized for the management of soil salinity.