Abstract
Non-destructive soil water content determination is a fundamental component for many agricultural and environmental applications. The accuracy and costs of the sensors define the measurement scheme and the ability to fit the natural heterogeneous conditions. The aim of this study was to evaluate five commercially available and relatively cheap sensors usually grouped with impedance and FDR sensors. ThetaProbe ML2x (impedance) and ECH2O EC-10, ECH2O EC-20, ECH2O EC-5, and ECH2O TE (all FDR) were tested on silica sand and loess of defined characteristics under controlled laboratory conditions. The calibrations were carried out in nine consecutive soil water contents from dry to saturated conditions (pure water and saline water). The gravimetric method was used as a reference method for the statistical evaluation (ANOVA with significance level 0.05). Generally, the results showed that our own calibrations led to more accurate soil moisture estimates. Variance component analysis arranged the factors contributing to the total variation as follows: calibration (contributed 42%), sensor type (contributed 29%), material (contributed 18%), and dry bulk density (contributed 11%). All the tested sensors performed very well within the whole range of water content, especially the sensors ECH2O EC-5 and ECH2O TE, which also performed surprisingly well in saline conditions.
Highlights
Non-destructive soil water content determination is a fundamental component of agricultural applications such as precision agriculture and irrigation scheduling [1,2]
Some of the values of a1 were outside of the commonly obtained range of values. This is supported by higher values of Root Mean Square Error (RMSE) for most of the water content data based on our own two-point calibrations (Table 3)
This was evident for sensors divided into two groups: (i) sensors operating at a frequency of 70 MHz
Summary
Non-destructive soil water content determination is a fundamental component of agricultural applications such as precision agriculture and irrigation scheduling [1,2]. Several techniques exist for automated continuous point-scale soil water content measurements. This study is focused on techniques based on dielectric characterization of the soil. Two publications related to sensors and their calibration and measurement accuracy for different soil conditions and influence of organic matter content were presented in 2016 [14,15]. Of these two methods, FDR is the more recent method and offers relatively accurate measurements for reasonable
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