Simultaneous use of newly adopted simple sensors for continuous measurements of soil moisture and salinity

Abstract

Methods available to measure salinity and moisture content in arid and semi-arid regions are limited because of the high salinities and very wide range of water contents (i.e. from saturation near the water table to air dry in the evaporation front). This paper is focused on the instrumentation employed in monitoring salt and moisture profiles in a column study which has wide applicability in salinity research. Experiments were conducted in a specially designed evaporation chamber which provided high evaporative demand as experienced in arid and semi-arid regions. Intensively instrumented soil columns with a constant shallow saline water table were used. Moisture content was measured by thermal conductivity and salinity by 4-electrode probe. In each case, instruments were manufactured specifically for the purpose in order to provide the desired degree of spatial resolution. Two soil types, sandy loam and clay loam, were used. Results indicated that thermal-conductivity probes measured water content over a wide range from saturation to 0.16 m³/m³ for clay loam and to 0.09 m³/m³ for sandy loam soil with great sensitivity (R² > 0.95) and were unaffected by salt accumulation. The 4-electrode probes provided reliable measurements (R² > 0.95) of the salinity of the soil solution for the range relevant to agricultural application. However, the accuracy of the probe decreased with the decreases in the water content after permanent wilting point.