MAPPING SALINITY USING RESISTIVITY AND ELECTROMAGNETIC INDUCTIVE TECHNIQUES

Abstract

The Wenner array and two terrain conductivity meters (EM31 and EM38) were used to demonstrate their potential for mapping field scale salinity. The Wenner configuration of electrodes (four probes) measured soil resistivity (inverse of conductivity) while the two terrain meters used electromagnetic inductive currents to measure conductivity directly. All instruments gave a clear delineation between areas of high and low salt content; this distinction could not be obtained from aerial photographs. The continuous recording EM31 conductivity meter proved to be the most rapid method for mapping saline areas, but could not be used to obtain detail on salt distribution with respect to depth. The shallower sensing EM38 gave a rapid response, but the prototype used was sensitive and required frequent scale adjustment. The assembled Wenner four-probe array was a bulky piece of equipment to handle and poor soil contact was experienced occasionally in drier soils. Resistance readings with the Wenner array were time-consuming, but the technique did offer the attractive advantage of measuring salt distribution with depth.