A LABORATORY EVALUATION OF WATERMARK ELECTRICAL-RESISTANCE AND CAMPBELL-SCIENTIFIC-229 HEAT DISSIPATION MATRIC POTENTIAL SENSORS

There is much interest in continuous recording of soil matric potentia l with porous matrix sensors for irrigation scheduling purposes. Water mark electrical resistance and Campbell Scientific 229 heat dissipatio n matric potential sensors were simultaneously tested in a modified pr essure chamber. Both sensors are suitable for automatic recording of c hanges in soil water content or matric potential. Initial indications are that individual sensor calibration will be unnecessary for irrigat ion scheduling purposes. The electrical resistance measurement was sho wn to be affected by soil salinity and temperature and to be dependent on wetting history. Moderate hysteresis of hear dissipation sensors w as recorded. Both the electrical resistance and the heat dissipation m easurement provided reliable estimates of soil matric potential in the range from -100 io 0 J.kg(-1) at various salinity levels. A minimum r eading interval of 3 min is recommended for the heat dissipation senso r to allow the block temperature to re-equilibrate.