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United States Department of Agriculture

Agricultural Research Service

Title: International Soil Moisture Sensor Comparison

Author
item Evett, Steven

Submitted to: Soil Water Monitoring
Publication Type: Book / Chapter
Publication Acceptance Date: January 1, 2005
Publication Date: April 1, 2005
Citation: Evett, S.R. 2005. International soil moisture sensor comparison. In: Charlesworth, P. editor. Soil Water Monitoring. Irrigation Insights No. 1, 2nd edition. Braddon, Australia: Land & Water Australia. p. 68-71.

Interpretive Summary: A four-year effort to compare and test soil moisture sensors is drawing to a close. The cooperative research project was sponsored by the International Atomic Energy Agency (IAEA) and included scientists from Australia, Austria, France, Tunisia, and the United States. The laboratory and field comparisons were desired by the IAEA to find if technologies existed that could replace the neutron thermalization method for soil profile water content estimation. Neutron thermalization measurements are done with the neutron moisture meter (NMM), a device invented 50 years ago for measurements at any depth(s) desired within an access tube placed vertically in the soil. Accurate profile water content measurements are crucial to determination of crop water use and irrigation infiltration, and thus are key to studies of crop water use efficiency and irrigation efficiency ' two important elements in the goal of producing more crop per drop in our increasingly water-short world. Soon after its invention the NMM was shown to be superior to standard gravimetric sampling due to its repeatability and large soil volume measured. The comparison studies focused on devices that measure soil electrical properties, which are related to the amount of water in the soil. Results revealed that there is not yet a suitable replacement for the NMM for soil water balance studies. Some alternative devices are too sensitive to soil temperature. Most produce highly variable readings in the field. Also, the alternative devices are difficult to field calibrate.

Technical Abstract: A four-year effort to compare and test soil moisture sensors is drawing to a close. The cooperative research project was sponsored by the International Atomic Energy Agency (IAEA) and included scientists from Australia, Austria, France, Tunisia, and the United States. The laboratory and field comparisons were desired by the IAEA to find if technologies existed that could replace the neutron thermalization method for soil profile water content estimation. Neutron thermalization measurements are done with the neutron moisture meter (NMM), a device invented 50 years ago for measurements at any depth(s) desired within an access tube placed vertically in the soil. Accurate profile water content measurements are crucial to determination of crop water use and irrigation infiltration, and thus are key to studies of crop water use efficiency and irrigation efficiency ' two important elements in the goal of producing more crop per drop in our increasingly water-short world. Soon after its invention the NMM was shown to be superior to standard gravimetric sampling due to its repeatability and large soil volume measured. Alternative devices studied all respond to soil electrical properties, which are response to water content. In general, the comparison studies revealed that there is not yet a suitable replacement for the NMM for soil water balance studies. Some alternative devices are too sensitive to soil temperature. Most measure such small volumes that they produce highly variable readings in the field, probably because they are sensing volumes smaller than the representative elemental volume for soil water content. Similarly, they are rendered sensitive to soil disturbance or voids caused by access tube installation. Also, the alternative devices are difficult to field calibrate.

Last Modified: 10/23/2014
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