TN-31 : Application of resistivity method for moisture estimation in top soil layer

Abstract

Use of resistivity method is well established in ground water exploration. Studies of unsaturated zone are important because they can provide information about soil moisture content in the subsurface. Soil moisture measurements play vital role for studies in the field of hydrology, Meteorology and agriculture etc. The occurrence of soil water in the root zone is important for optimum crop production. Conventional instruments for resistivity surveys are quite common and are already available. Though the nuclear techniques such as neutron probe are better suited for soil moisture studies, however, the costs and risks involved my somewhat limit their use for field studies on a wider scale. For general field use, resistivity techniques could provide a versatile approach, if, their applicability in soil moisture estimation could be established. The report also discusses various conventional and geophysical (Including nuclear) methods, and their usefulness in soil moisture studies.

Electrical properties of water such as conductivity and dielectric constant which form basis of a number of electrical and electronic moisture meters are defined. Resistivity investigations were carried out using Megger at the Campus of National Institute of Hydrology, Roorkee. Electrode separation of 0. 25 -2. 5 meter was taken in electrical soundings with Wenner Configuration. Soil moisture measurements were taken by Neutron moisture probe. An attempt was made to study the effect of climatic conditions on moisture and resistivity of the soil layers and develop a strategy for employing electrical methods for estimating soil moisture.

Results obtained during the course of these investigations indicate that the electrical methods could be used for estimation of soil moisture. Soil moisture measurements carried out using neutron probe and electrical resistivity meter have also been correlated. These investigations indicate an inverse relationship between soil moisture content and corresponding soil resistivity observations. However, further studies on these lines on a comprehensive basis would be necessary, for arriving at definite conclusions.