Evaluation of temperature and bypass flow sensitivity of tensiometers in a field soil

Field tensiometry is used to estimate the energy status of soil water. Due to the recent availability of accurate pressure transducers and data loggers, matric potential data can be obtained with high temporal resolution. To reassess the accuracy of tensiometer readings, we investigated the effect of temperature and bypass flow along the tensiometer wall on matric potential estimates in the field with tensiometers using different tube materials and with varying wall thicknesses and lengths. Temperature changes introduced errors of the same magnitude as the mean measured matric potential values. These errors did not depend on the length of the tensiometer tube protruding out of the soil, but on the material used for the tubes. Bypass flow along tensiometer tubes was significant for long and intense rain showers. Horizontally oriented tensiometers which were protected with polystyrene plates against the weather were least influenced by temperature and bypass flow. We recommend to insulate vertically installed tensiometers against temperature and radiation or to take readings during the night.