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United States Department of Agriculture

Agricultural Research Service

Research Project: MANAGING AGRICULTURAL WATER QUALITY IN FIELDS AND WATERSHEDS: NEW PRACTICES AND TECHNOLOGIES Title: Measurement of soil water content with dielectric dispersion frequency

Authors
item Xu, Jinghui -
item Logsdon, Sally
item Ma, Xiaoyi -
item Horton, Robert -
item Han, Wenting -

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 11, 2014
Publication Date: N/A

Interpretive Summary: A device was built to measure soil water content that would be accurate even in dry or salty soil, that cause problems with other soil water probes. The device was accurate for a range of temperatures as well. At first the information is primarily of interest to scientists. As the device is perfected and cost is reduced, the information would be of interest to consultants who monitor soil water for irrigation timing, crop productivity, appropriate pesticide function, survival of beneficial and test mesofauna, etc.

Technical Abstract: Frequency domain reflectometry (FDR) is an inexpensive and attractive methodology for repeated measurements of soil water content (SWC). Although there are some known measurement limitations for dry soil and sand, a fixed-frequency method is commonly employed using commercially available FDR probes. The purpose of our study was to determine if the soil dielectric spectrum could be used to measure changes in SWC. A multi-frequency FDR probe was constructed with a 6mm diameter and the soil dielectric spectrum was obtained. Using the dielectric spectrum, the dielectric dispersion frequency (DDR) was determined. It was discovered that changes in DDR were highly correlated with changes in the SWC and a polynomial equation was developed describing the relationship. The effectiveness of DDR for SWC measurement was evaluated for three soils and a sand over a range of SWC. The effects of soil temperature and soil salinity were also evaluated. Accurate measurements of SWC were obtained even in dry soil and sand. Soil temperature and soil salinity had no measureable effects on SWC determination. The use of DDR for SWC determination should be an effective and accurate methodology especially when dry soils, soil temperature, and/or soil salinity could potentially cause problems with the SWC measurements.

Last Modified: 7/28/2014
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