|Evett, Steven - Steve|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 2/7/2007
Publication Date: 2/1/2008
Citation: Laurent, J., Evett, S.R. 2008. Trime® FM3 moisture meter and T3 access tube probe. In: Evett, S.R., Heng, L.K., Moutonnet, P., Nguyen, M.L., editors. Field Estimation of Soil Water Content: A Practical Guide to Methods, Instrumentation, and Sensor Technology. IAEA-TCS-30. International Atomic Energy Agency, Vienna, Austria. ISSN 1018-5518. p. 91-100.
Interpretive Summary: A major user of soil water estimation methods for agricultural research and development is the joint division of the United Nations Food and Agriculture Organization and the International Atomic Energy Agency. At the invitation of the joint division, the Soil and Water Management Research Unit of the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas, guided research in Texas, California and Austria aimed at comparing and quantifying the performance of currently available soil water sensing methods. This chapter details the theory and application of a soil water sensor that relies on the electrical properties of soil as they are influenced by its water content. The sensor is used by lowering it into a plastic tube that has been inserted into the soil, taking readings every six inches. The accuracy of the sensor was determined to be less than that available from direct measurements involving soil sampling and drying, but the sensor took less time and labor than direct sampling. The sensor was found to be influenced by salts in irrigated soils, by clay content and type, and by soil temperature. Guidance is given for field calibration to overcome some of these problems. Directions for installation of the plastic tubes in hard soils are given, as are directions for taking readings and reducing the data to useful estimates of soil water content.
Technical Abstract: An expert group from five nations and three continents did comparative trials of soil water sensing methods under laboratory and field conditions at the behest of the joint division of the International Atomic Energy Agency and FAO, resulting in a nine-chapter guide to field estimation of soil water content. Chapter 6 gives a detailed look at the Trime T3 access tube probe, which relies on time domain reflectometry (TDR) in so far as it injects a fast rise time electrical pulse into a waveguide that is placed at user-chosen depths within a plastic access tube in the soil. The probe was found to be a quasi-TDR device because it does not completely capture the reflected wave form, nor does it apply complete graphical analysis as does conventional TDR. The authors conclude that this is why the sensor was found to be greatly influenced by salts in soils, by clay content and type, and by soil temperature. Guidance is given for field calibration to overcome some of these problems. Directions for installation of the plastic tubes in hard soils are given, as are directions for taking readings and reducing the data to useful estimates of soil water content. Examples of calibrations in clay soils compared with the factory calibration show that factory calibrations cannot be used with confidence.