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United States Department of Agriculture

Agricultural Research Service

Research Project: IRRIGATION MANAGEMENT AND AUTOMATION FOR INCREASED WATER USE EFFICIENCY

Location: Soil and Water Management Research

Title: Comparison of soil water sensing methods for irrigation management and research

Authors
item Evett, Steven
item Howell, Terry
item Tolk, Judy

Submitted to: Proceedings of the Central Plains Irrigation Conference
Publication Type: Proceedings
Publication Acceptance Date: February 16, 2007
Publication Date: February 27, 2007
Citation: Evett, S.R., Howell, T.A., Tolk, J.A. 2007. Comparison of soil water sensing methods for irrigation management and research. In: Proceedings of the Central Plains Irrigation Conference, February 27-28, 2007, Kearney, Nebraska. p. 1-19.

Interpretive Summary: As irrigation water resources decrease and deficit irrigation becomes more common across the Great Plains, greater accuracy in irrigation scheduling will be required. New management practices for deficit irrigation will require more accurate assessments of soil water content if success is to be ensured. This study compared several commercial soil water sensing systems, four of them based on the electromagnetic (EM) properties of soil as influenced by soil water content, versus the venerable neutron moisture meter (NMM). The NMM is not practical for on-farm irrigation management due to cost and regulatory issues. Unfortunately, our studies indicated that the EM sensors were not useful for irrigation management due to inaccuracy and excessive variability of readings. A new generation of EM sensors should be developed to overcome the problems of those currently available. Scientists and engineers of the Soil and Water Management Research Unit are currently engaged in development and testing of new sensors.

Technical Abstract: As irrigation water resources decrease and deficit irrigation becomes more common across the Great Plains, greater accuracy in irrigation scheduling will be required. Researchers investigating deficit irrigation practices and developing management practices must also have accurate measures of soil water content – in fact, the two go hand-in-hand. New management practices for deficit irrigation will require more accurate assessments of soil water content if success is to be ensured. This study compared several commercial soil water sensing systems, four of them based on the electromagnetic (EM) properties of soil as influenced by soil water content, versus the venerable neutron moisture meter (NMM). The EM sensors were all less precise and less accurate in the field than was the NMM. Variation in water contents from one measurement location to the next was much greater for the EM sensors and was so large that these sensors are not useful for determining the amount of water to apply. The NMM is still the only sensor that is suitable for irrigation research. However, the NMM is not practical for on-farm irrigation management due to cost and regulatory issues. Unfortunately, our studies indicate that the EM sensors are not useful for irrigation management due to inaccuracy and variability. A new generation of EM sensors should be developed to overcome the problems of those currently available. In the meantime, many farmers are successfully using irrigation scheduling based on crop water use estimates from weather station networks and reference ET calculations. When used in conjunction with direct field soil water observations to avoid over irrigation, the ET network approach has proved useful in maximizing yields.

Last Modified: 4/17/2014
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