Evaluation of a line heat dissipation sensor for measuring soil matric potential

The accuracy and operational limits of a new heat dissipation sensor for measuring soil matric potential are evaluated. The measurement is based on the rate of temperature rise from a line heat source embedded in a cylindrical porous ceramic that is in equilibrium with soil water. Different heating currents or times can be accounted for by basing calibration on sensor thermal conductivity rather than temperature rise. Six sensors were calibrated against pressure plate and psychrometer measurements of matric potential. Inverse of sensor thermal conductivity was linearly related to the logarithm of matric potential between - 10 and - 1200 J kg(-1). This range of measurable matric potentials is much larger than previous heat dissipation sensor designs. The heat dissipation sensor was accurate to within 20% of the independently measured matric potential. Normalizing sensor readings by sensor thermal conductivity after oven drying results in a calibration that accounts for between-sensor variability. In a growth chamber experiment with fluctuating soil temperatures, heat dissipation sensor estimates of soil matric potential compared favorably with tensiometer and psychrometer measurements. Heat dissipation sensors based on this design appear useful when a wide range of matric potentials needs to be studied.