Evaluation of temperature and bypass flow sensitivity of tensiometers in afield soil

Field tensiometry is used to estimate the energy status of soil water. Due to the recent availability of accurate pressure transducers and data logger s, matric potential data can be obtained with high temporal resolution. To reassess the accuracy of tensiometer readings, we investigated the effect o f temperature and bypass flow along the tensiometer wall on matric potentia l estimates in the field with tensiometers using different tube materials a nd with varying wall thicknesses and lengths. Temperature changes introduce d errors of the same magnitude as the mean measured matric potential values . These errors did not depend on the length of the tensiometer tube protrud ing out of the soil, but on the material used for the tubes. Bypass flow al ong tensiometer tubes was significant for long and intense rain showers. Ho rizontally oriented tensiometers which were protected with polystyrene plat es against the weather were least influenced by temperature and bypass flow . We recommend to insulate vertically installed tensiometers against temper ature and radiation or to take readings during the night. (C) 1999 Elsevier Science B.V. All rights reserved.