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Performance of a Capacitance‐Type Soil Water Probe in a Well‐Drained Sandy Soil
Author(s) -
Bandaranayake W. M.,
Parsons L. R.,
Borhan M. S.,
Holeton J. D.
Publication year - 2007
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2006.0282
Subject(s) - soil water , capacitance probe , soil science , water content , environmental science , entisol , bulk density , field capacity , capacitance , porosity , fertigation , irrigation scheduling , hydrology (agriculture) , irrigation , chemistry , geology , geotechnical engineering , electrode , agronomy , biology
Most soils in the Central Florida Ridge (CFR) area are Entisols that contain >95% sand, <3% clay, and <2% organic matter. Field capacity (θ fc ) is commonly ∼0.08 m 3 m −3 Therefore, accurate estimation of soil water content (θ v ) is important in these soils. The objective of this study was to evaluate the performance of ECH 2 O probes when estimating θ v for scheduling irrigation in CFR soils. Probes were tested for (i) probe‐to‐probe output variability, (ii) soil volume sampled, (iii) sensitivity to salinity, temperature, and air pockets close to the sensor surface, (iv) pockets of very dry soil close to the sensor surface, and (v) performance after installation in the field. According to the calibration, a 1% change in water content corresponds to a probe output of 17 mV. Laboratory testing suggested that output variability from probe to probe can be a problem in these soils. The sampling volume of the probe was within 1.5 cm from either side of the sensor surface. Salinity induced during fertigation increased the output by about 200 mV, and for each 1°C drop in temperature, the sensor output dropped by 2.3 mV. When the bulk density was changed from 1.56 to 0.94 Mg m −3 , the output decreased by 3.5 MV for each 1% drop in air‐filled porosity. When very dry soil lenses with <0.01 m 3 m −3 θ v were associated with the probe surface, the probe failed to sense the wet soil even 1 cm away from the sensor surface. Sensor failure was common due to water leaking into the circuit when sealing material deteriorated or casing material was damaged by insects. These issues need to be addressed before the probes can be considered reliable to estimate θ v or used in automated irrigation.