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Open AccessFeature PaperArticle

The Effect of Soil Iron on the Estimation of Soil Water Content Using Dielectric Sensors

1
Laboratory of Agricultural Hydraulics, Department of Natural Resources Management and Agricultural Engineering, Agricultural University of Athens, 75 Iera Odos, PC 11855 Athens, Greece
2
Laboratory of Economic Geology and Geochemistry, Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, PC 15784 Athens, Greece
3
Laboratory of Soil Science and Agricultural Chemistry, Department of Natural Resources Management and Agricultural Engineering, Agricultural University of Athens, 75 Iera Odos, PC 11855 Athens, Greece
*
Author to whom correspondence should be addressed.
Water 2020, 12(2), 598; https://doi.org/10.3390/w12020598
Received: 21 November 2019 / Revised: 18 January 2020 / Accepted: 20 February 2020 / Published: 22 February 2020
(This article belongs to the Special Issue Study of the Soil Water Movement in Irrigated Agriculture)
Nowadays, the estimation of volumetric soil water content (θ) through apparent dielectric permittivity (εa) is the most widely used method. The purpose of this study is to investigate the effect of the high iron content of two sandy loam soils on estimating their water content using two dielectric sensors. These sensors are the WET sensor operating at 20 MHz and the ML2 sensor operating at 100 MHz. Experiments on specific soil columns, in the laboratory, by mixing different amounts of water in the soils to obtain a range of θ values under constant temperature conditions were conducted. Analysis of the results showed that both sensors, based on manufacturer calibration, led to overestimation of θ. This overestimation is due to the high measured values of εa by both sensors used. The WET sensor, operating at a lower frequency and being strongly affected by soil characteristics, showed the greatest overestimation. The difference of εa values between the two sensors ranged from 14 to 19 units at the maximum actual soil water content (θm). Compared to the Topp equation, the WET sensor measures 2.3 to 2.8 fold higher value of εa. From the results, it was shown that the relationship θma0.5 remained linear even in the case of these soils with high iron content and the multi-point calibration (CALALL) is a good option where individual calibration is needed. View Full-Text
Keywords: apparent dielectric permittivity; soil water content; dielectric sensor; specific calibration apparent dielectric permittivity; soil water content; dielectric sensor; specific calibration
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MDPI and ACS Style

Kargas, G.; Londra, P.; Anastasatou, M.; Moustakas, N. The Effect of Soil Iron on the Estimation of Soil Water Content Using Dielectric Sensors. Water 2020, 12, 598.

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