TN-56 : Resistivity techniques for monitoring soil salinity

Abstract

Soil salinity problem in agricultural fields arises due to excessive soluble salts present in the soil, the inorganic electrolytes in the soil solution being the major contributors. Conventionally the salinity of the soil is measured in the laboratory for which soil and/or soil water samples may be collected and analysed in different ways, which involves much labour, time and expenses. For these reasons, a rapid, inexpensive in-situ or remotely sensing method which makes use of the spatially varying soil salinity-bulk electrical conductivity relation, will be of great help in modern agriculture. The resistivity method, which has served the groundwater exploration purposes for nearly a century has been proved to be of much use in establishing the soil salinity-electrolytic conduction relation.

In this report the relationship between conductivity and soil salinity, why and how the soil resistivity is convert ed into the conductivity values, the advantages of the field techniques over the laboratory techniques are presented. Various methods applicable for in-situ measurement of soil salinity have been briefly discussed. For the bulk soil conductivity sensors, the basic concepts, theory and principles, effects of water content and entrapped air on electrical conductivity-salinity relationship, the various calibration procedures and field application of four-electrode method have been comprehensively reviewed. Light has also been thrown upon the new techniques such as Electro Magnetic (EM) induction method and Time Domain Reflectometry (TDR) method with their advantages and disadvantages outlined. Finally a comparison of various methods for measuring salinity intrinsically, has also been made.