Transducer for in situ measurement of soil water conductivity.

Abstract

In recent years, several attempts have been made to develop instrumentation to aid in the measurement of soil water electrical conductivity. Each of the instruments have specific limitations. This dissertation discusses the available methods of measuring this parameter and indicates the limitations of the transducers which have been described in the literature. Also, discussed are the basic theories of operation of these transducers and definitions related to soil salinity in general. The major objective of this research was to develop a new transducer which would be a significant improvement over existing types of instrumentation. It is believed that this research has led to the development of two transducers of different geometries which can assess the soil water conductivity over a wider range of matric potential just as rapidly and accurately as the next best unit. At the same time the new transducers incorporate automatic temperature compensation which has not been done by any other field instrumentation of its type. Also presented, is the application of heat transfer theories to the diffusion of ions from the transducer to the surrounding environment, Application of this theory allows one to predict how the transducer will respond to a step change in ion concentration in an unsaturated soil system where the only process involved is diffusion. Good agreement between experimental measurements and predicted response indicates that the model may also be useful in further refinements of the transducer.