Some field instruments suitable for the automated measurement of thermal and hydraulic properties of soil

Abstract

SUMMARYThree types of field instrument are described that are suitable for the automated and replicatedin situmeasurement of the soil properties: temperature, thermal conductivity and water pressure. Novel aspects of their design and construction are discussed, as are details of their installation and precautions necessary for successful use in the field. The principle of operation of each type of instrument is described and the method of controlling several instruments of the same type via a computer-based data acquisition system is indicated. Their accuracy and performance under field conditions are shown to be very adequate. Determination errors are approximately 0·1 K in the range 0–35 °C for temperature, 6–8% for thermal conductivity, and 1 mm water for water pressure, with a time constant of about 2 sec in a silty clay loam soil; reliability is measured as two sensor failures out of 236 over an operating period of several months. Examples are given of data collected during their deployment in an experiment to determine the physical effects of tillage on soil.