Heat‐Pulse Method for Soil Water Content Measurement

The heat‐pulse method measures soil volumetric water content (θ) based on the linear relationship between soil volumetric heat capacity ( C ) and θ. Previous work suggested that this method was more appropriate for determining change of θ rather than its absolute value. In this study, we demonstrate that the heat‐pulse method can give accurate θ estimation when values for the specific heat of the soil solids ( c s ) are determined using the heat‐pulse method. Heat‐pulse measurements were performed on packed columns of three soils with a wide range of bulk density (ρ b ) and θ. When the commonly used c s value (0.725 kJ kg −3 K −1 ) was used, the heat‐pulse method overestimated θ by 0.052 m 3 m −3 on average. However, when c s values determined from heat‐pulse measurements on oven‐dried soil were used, the heat‐pulse method provided accurate θ results (−0.006 m 3 m −3 average error). Using soil‐specific, heat‐pulse determined c s values also reduced the average root mean square error (RMSE) in θ for the three soils from 0.061 to 0.039 m 3 m −3