Time Domain Reflectometry Field Measurements of Soil Water Content and Electrical Conductivity

Abstract

Simultaneous measurements of volumetric water content and bulk electrical conductivity were made using time domain reflectometry (TDR) with a single parallel transmission line (PTL) imbedded in the soil. Sixty PTL's were installed at five depths in 12 existing lysimeter plots, irrigated with different amounts of water at two salt concentrations (1.3 and 3.1 dS/m). The water content measurements obtained with TDR showed a good relationship to gravimetric determinations (r2 = 0.84) and were comparable to neutron probe measurements. The TDR measurements of bulk soil electrical conductivity were similar to the measurements of the same soil physical property measured with the four-probe electrode technique. The relation between bulk soil electrical conductivity and the conductivity of the soil solution is discussed. The importance of measuring both soil water content and salinity in a nondestructive manner on the same sampling volume, enabling repeated in situ measurements is stressed.