Measuring peat moisture content using the dual-probe heat pulse technique

The dual-probe heat pulse (DPHP) technique for measuring soil volumetric moisture content (theta(v)) is evaluated for use in peat soils with very high organic matter contents. The method has a greater sensitivity in peat soils compared with mineral soils and excellent resolution is possible, even at moisture contents as high as 90% by volume. Advantages of the DPHP technique are that sensors are simple to construct from inexpensive parts and calibration is not required since the method is based on a physical model of radial heat flow in soil. A multiplexer method was developed to allow multiple probes to be deployed in the field. DPHP measurements of theta(v) for small peat samples compared closely to reference measurements made using the gravimetric method, and in the field were similar to results obtained using a time domain reflectometry (TDR) method. Peat soils display a high level of spatial variation in theta(v) at the scales of both DPHP and TDR probes, so that multiple probes of each type are required for adequate spatial sampling of theta(v). Rapid changes in peat moisture content were recorded following rainfall infiltration events yet moisture storage did not remain elevated following rainfall, even for peat that was very dry.