Articles
WET-SENSOR PORE WATER EC CALIBRATION FOR THREE HORTICULTURAL SOILS
Article number
691_97
Pages
789 – 796
Language
English
Abstract
The WET-sensor is a frequency domain dielectric sensor that measures permittivity, conductivity and temperature, which can be used for monitoring soil water content and electrical conductivity in horticulture.
By using a specific model it measures pore water conductivity as well.
However, under practical circumstances, large errors have been observed using the existing model.
The purpose of this study was to obtain a empirical correction for this model and to investigate the nature of the errors, so horticultural growers can use the WET-sensor to measure pore water EC in-situ.
Using 36 potted samples of sand, clay and peat, the relation between permittivity, bulk EC and pore water EC was studied in a laboratory over a temperature range from 19-22 oC and a pore water EC range from 4 12 mS/cm.
This resulted in an adaptation of the constant in the existing model and an extra second order polynomial correction factor.
After temperature correction, an overall linear fit with a coefficient of 0.9948 was found at a reasonable correlation (0.79). Errors may occur up to ±40%, but for permittivity values larger than 20, errors have a maximum of ±15%. The overall standard deviation is 15%, which is in accordance with simulated results.
For growers using relatively wet soils at water contents above 20%, the WET-sensor can be used to measure pore water EC in situ with a reasonable accuracy.
Further study is needed to explore this correction at larger temperature ranges and for more soil types.
By using a specific model it measures pore water conductivity as well.
However, under practical circumstances, large errors have been observed using the existing model.
The purpose of this study was to obtain a empirical correction for this model and to investigate the nature of the errors, so horticultural growers can use the WET-sensor to measure pore water EC in-situ.
Using 36 potted samples of sand, clay and peat, the relation between permittivity, bulk EC and pore water EC was studied in a laboratory over a temperature range from 19-22 oC and a pore water EC range from 4 12 mS/cm.
This resulted in an adaptation of the constant in the existing model and an extra second order polynomial correction factor.
After temperature correction, an overall linear fit with a coefficient of 0.9948 was found at a reasonable correlation (0.79). Errors may occur up to ±40%, but for permittivity values larger than 20, errors have a maximum of ±15%. The overall standard deviation is 15%, which is in accordance with simulated results.
For growers using relatively wet soils at water contents above 20%, the WET-sensor can be used to measure pore water EC in situ with a reasonable accuracy.
Further study is needed to explore this correction at larger temperature ranges and for more soil types.
Authors
J. Balendonck, M.A. Bruins, M.R. Wattimena, W. Voogt, A. Huys
Keywords
agriculture, soil, electrical conductivity, frequency domain, dielectric sensor
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