Abstract
An in situ field test on nine commonly-used soil water sensors was carried out in a sandy loam soil located in the Potato Research Center, Fredericton, NB (Canada) using the gravimetric method as a reference. The results showed that among the tested sensors, regardless of installation depths and soil water regimes, CS615, Trase, and Troxler performed the best with the factory calibrations, with a relative root mean square error (RRMSE) of 15.78, 16.93, and 17.65%, and a r2 of 0.75, 0.77, and 0.65, respectively. TRIME, Moisture Point (MP917), and Gopher performed slightly worse with the factory calibrations, with a RRMSE of 45.76, 26.57, and 20.41%, and a r2 of 0.65, 0.72, and 0.78, respectively, while the Gypsum, WaterMark, and Netafim showed a frequent need for calibration in the application in this region.
Highlights
In the past few decades, a great number of automated techniques for point measurement of soil water content have been developed and tested because of the important role soil water content plays in guiding the management of irrigation and drainage [1,2,3]
Domain Reflectometry (TDR), measuring soil water content through measuring the travel time of an electromagnetic pulse along the metal rods of the waveguide, the time is determined by the soil bulk electrical permittivity which is strongly influenced by soil water, and (b) frequency domain reflectometers (FDR), similar to TDR but relying on reflected pulse reaching a set voltage rather than waveform analysis in TDR [5]; (vi) neutron method, consisting of a radioactive fast neutron source probe and a helium-3 detector, estimating soil water by the recorded count of thermal neutrons which are thermalized by the hydrogen present in the soil [3]
The neutron method was found to perform better than the dielectric methods in previous research [8] and was suggested that a local soil type-based calibration of the neutron method could make this approach appealing [3], our research indicated that this method performed well but not as good as some of the dielectric methods such as CS615 and Trase
Summary
In the past few decades, a great number of automated techniques for point measurement of soil water content have been developed and tested because of the important role soil water content plays in guiding the management of irrigation and drainage [1,2,3]. A certain amount of testing is normally conducted during the development of each sensor or some lab calibration is done by end users, due to the differences in design and functionality, each sensor may perform differently when used in real measurement operations in a specific region The reliability of those tests is limited by specific lab configurations and soil types [5,6,7]. Leib et al [8] did a similar field comparison of several soil moisture sensors including Irrometer Watermarks (The Irrometer Co., Riverside, CA, USA), EnviroScan
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