Evaluating methods for measuring the mean soil temperature

Measurements of temperatures that are averaged or integrated over long time spans are needed for a variety of purposes such as soil resource inventory and climate studies. Mean temperatures usually are obtained in a two-step process of observation and numerical integration of periodic values. Pallmann introduced a technique using a temperature driven chemical reaction to integrate temperature over a period time. In this research, we illustrated the field application of the Pallmann method to measure mean soil temperature in a long-term climate change investigation project. The accuracy and consistency of the Pallmann method were evaluated by comparing two other temperature measurement methods: thermistor sensor and diffusion-cell method. The consistency of the Pallmann method is quite good. On average, the mean annual soil temperatures measured by the Pallmann method were 0.27 °C lower than those measured by the diffusion-cell method and were 0.64 °C higher than those measured by the thermistor sensor method. While statistical analysis showed that there was significant difference between the means of these three methods, the Pallmann method may better reflect the real ecological processes in soil in comparison with the arithmetic-mean temperature measured by the thermal sensors. It is an ideal method for studying the spatial variation in soil temperature and long-term climate changes.