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United States Department of Agriculture

Agricultural Research Service

Research Project: IRRIGATION MANAGEMENT AND AUTOMATION FOR INCREASED WATER USE EFFICIENCY Title: An overview of soil water sensing technologies and problems

item Evett, Steven

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2007
Publication Date: March 1, 2007
Citation: Evett, S.R. 2007. An overview of soil water sensing technologies and problems. International Soil Moisture Sensing Technology Conference: Current and future research directions in soil moisture sensing, March 19-21, 2007, Honolulu, Hawaii.

Technical Abstract: An expert group from five nations and three continents did comparative trials of soil water sensing methods under laboratory and field conditions for the International Atomic Energy Agency. Important conclusions of the expert group include: 1) The field-calibrated neutron moisture meter (NMM) remains the most accurate and precise method for soil profile water content determination in the field and is the only indirect method capable of providing accurate soil water balance data with a minimal number of access tubes; 2) Those electromagnetic (EM) sensors known as capacitance sensors exhibit much more variability in the field than either the NMM or direct soil water measurements; and they are not recommended for soil water balance studies due to the impractically large numbers of access tubes and sensors required,and because they are rendered inaccurate by changes in soil bulk electrical conductivity (including temperature effects) that often occur in irrigated soils, even when using soil-specific calibrations; 3) All sensors must be field calibrated in order to obtain reasonable accuracy; 4) The one exception to conclusion three is conventional time domain reflectometry (TDR, with waveform capture and graphical analysis); 5) With the possible exception of tensiometers and the granular matrix resistance sensors, none of the sensors studied is practical for on-farm irrigation scheduling; they are either too inaccurate (capacitance sensors) or too costly and difficult to use (TDR and NMM); and 6) For research studies, only the NMM, conventional TDR and direct measurements have acceptable accuracy. With the problems well understood, research and development of new sensor systems to overcome these problems can proceed.

Last Modified: 10/23/2014
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