Abstract
Soil water content (SWC) monitoring is often used to optimize agricultural irrigation. Commonly, capacitance sensors are used for this task. However, the factory calibrations have been often criticized for their limited accuracy. The aim of this paper is to test the degree of improvement of various sensor- and soil-specific calibration options compared to factory calibrations by taking the 10HS sensor as an example. To this end, a two-step sensor calibration was carried out. In the first step, the sensor response was related to dielectric permittivity using calibration in media with well-defined permittivity. The second step involved the establishment of a site-specific relationship between permittivity and soil water content using undisturbed soil samples and time domain reflectometry (TDR) measurements. Our results showed that a model, which considered the mean porosity and a fitted dielectric permittivity of the solid phase for each soil and depth, provided the best fit between bulk permittivity and SWC. Most importantly, it was found that the two-step calibration approach (RMSE: 1.03 vol.%) provided more accurate SWC estimates compared to the factory calibration (RMSE: 5.33 vol.%). Finally, we used these calibrations on data from drip-irrigated almond and apple orchards and compared the factory calibration with our two-step calibration approach.
Highlights
Efficient irrigation management is essential for reducing water consumption
The results show that the use of a universal instead of a sensor-specific sensor response permittivity (SRP) model in combination with the complex refractive index model (CRIM)-4 model resulted in a small difference in soil water content (SWC) predictions with an root mean square error (RMSE) of 0.25 vol.% and a mean difference of 0.24 vol.%
The different SWC prediction variants based on the two-step calibration approach that were considered are: (i) sensor-specific SRP models combined with the Complex Refractive Index Model 4 (CRIM-4) model, (ii) a universal model combined with the CRIM-4 model, (iii) a universal SRP model obtained14with
Summary
Efficient irrigation management is essential for reducing water consumption. To this end, real-time monitoring of soil water content (SWC) is essential to optimize the amount and timing of water irrigation [1,2]. One the solution to of compensate forcontent this effect would beifto calibrate each sensor which accuracy the soil water measurements thisdirectly is not considered [12,13] This is time each consuming oftenwith not solution to compensate for this[14]. Use of TDRusing measurements calibration accounting for avariations in key soil properties can the be established a limited should be preferred because of its ability to directly provide dielectric permittivity and the number of soil samples. To this end, we carried out sensor-specific calibrations with 10HS sensors using reference media media with well-known dielectric properties and determined permittivity-SWC reference with well-known dielectric properties and determined permittivity-SWC relationships relationships using undisturbed soil samples and TDR measurements.
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