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United States Department of Agriculture

Agricultural Research Service


Location: Agroecosystems Management Research

Title: FDR probe structure influence on the soil dielectric spectrum measurement

item Xu, Jinghui
item Ma, Xiaoyi
item Logsdon, Sally
item Horton, Robert

Submitted to: Transactions of the Chinese Agricultural Machinery
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2014
Publication Date: 4/28/2014
Citation: Xu, J., Ma, X., Logsdon, S.D., Horton, R. 2014. FDR probe structure influence on the soil dielectric spectrum measurement. Transactions of the Chinese Agricultural Machinery. 45(1):102-107.

Interpretive Summary: Irrigation efficiency can be improved by only watering when the soil is dry. Soil water sensors could be used to automatically trigger the start of irrigation when the soil is dry, but the sensors are expensive. The cost of the sensors could be reduced by using the dielectric spectrum, but the senor response is affected by needle length and spacing. The sensor accuracy could be improved by using short needles. This information is of interest to researchers and companies who develop soil water sensors for use with irrigation equipment. As the sensors become further developed, producers would benefit by using less irrigation water.

Technical Abstract: The soil dielectric spectrum are related to the soil physical properties, and those are affected by the structure of the probe too. In order to determine how the probe structure influence the soil dielectric spectrum measurement, the two kinds of soils were measured at four water content level by 10 mm and 14 mm spacing needle at 28 mm probe length,28 mm and 45 mm length needle at 10 mm spacing. It has been confirmed that the probe spacing has no effect on the soil dielectric spectrum measurement above 31. 2 MHz by comparing the dielectric spectrums, and the length of the probe can affect the real or imaginary part of the soil dielectric spectrum in the range of 0.001 ~ 3 GHz. The research shows that the spacing of needle is not the key factor to the soil dielectric property measurement within a certain spacing, and the length of the probe has a greater influence on the soil dielectric property measurement. The smaller of the probe length, the larger of the dielectric relaxation frequency. Therefore, the probe length is the important factor that affect soil dielectric measurements. The FDR probe should be shorter, it is good to improve the measurement accuracy and environmental adaptation.

Last Modified: 06/23/2017
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