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Field Calibrations of Soil Moisture Sensors in a Forested Watershed
Natural Resources and Environmental Management Department, University of Hawaii-Manoa, Honolulu, HI 96822, USA
* Author to whom correspondence should be addressed.
Received: 28 April 2011; in revised form: 20 May 2011 / Accepted: 7 June 2011 / Published: 16 June 2011
Abstract: Spatially variable soil properties influence the performance of soil water content monitoring sensors. The objectives of this research were to: (i) study the spatial variability of bulk density (ρb), total porosity (θt), clay content (CC), electrical conductivity (EC), and pH in the upper Mākaha Valley watershed soils; (ii) explore the effect of variations in ρb and θt on soil water content dynamics, and (iii) establish field calibration equations for EC-20 (Decagon Devices, Inc), ML2x (Delta-T-Devices), and SM200 (Delta-T-Devices) sensors to mitigate the effect of soil spatial variability on their performance. The studied soil properties except pH varied significantly (P < 0.05) across the soil water content monitoring depths (20 and 80 cm) and six locations. There was a linear positive and a linear inverse correlation between the soil water content at sampling and ρb, and between the soil water content at sampling and θt, respectively. Values of laboratory measured actual θt correlated (r = 0.75) with those estimated from the relationship θt = 1 − ρb/ρs, where ρs is the particle density. Variations in the studied soil properties affected the performance of the default equations of the three tested sensors; they showed substantial under-estimations of the actual water content. The individual and the watershed-scale field calibrations were more accurate than their corresponding default calibrations. In conclusion, the sensors used in this study need site-specific calibrations in order to mitigate the effects of varying properties of the highly weathered tropical soils.
Keywords: variable soil properties; soil water content; sensor field calibration; tropical soils
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Cite This Article
MDPI and ACS Style
Abbas, F.; Fares, A.; Fares, S. Field Calibrations of Soil Moisture Sensors in a Forested Watershed. Sensors 2011, 11, 6354-6369.
Abbas F, Fares A, Fares S. Field Calibrations of Soil Moisture Sensors in a Forested Watershed. Sensors. 2011; 11(6):6354-6369.
Abbas, Farhat; Fares, Ali; Fares, Samira. 2011. "Field Calibrations of Soil Moisture Sensors in a Forested Watershed." Sensors 11, no. 6: 6354-6369.