Soil Profile Water Content Determination: Sensor Accuracy, Axial Response, Calibration, Temperature Dependence, and Precision

ABSTRACT TDR-probes are widely used to monitor water content changes in a soil profile (ΔW). Frequently, probes are placed at just three depths. This raises the question how well such a setup can trace the true ΔW. To answer it we used a 2 m deep high precision weighing lysimeter in which TDR-probes are installed horizontally at 20, 60 and 120 cm depth (one per depth). ΔW-data collected by weighing the lysimeter vessel were taken as the true values to which ΔW-data determined with the TDR-probes were compared. We obtained the following results: There is a time delay in the response of the TDR-probes to precipitation, evaporation, transpiration or drainage, because a wetting or drying front must first reach them. Also, the TDR-data are more or less point measurements which are then extrapolated to a larger soil volume. This frequently leads to errors. For these reasons TDR-probes at just three depths cannot provide reliable data on short term (e.g. daily) changes in soil water content due to the above processes. For longer periods (e.g. a week) the data are better, but still not accurate enough for serious scientific studies.

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Setpoints for Potato Irrigation in Sandy Soils Using Real-Time, Continuous Monitoring of Soil-Water Content in Soil Profile

Journal of Crop Improvement ◽

10.1080/15427520701885311 ◽

2008 ◽

Vol 21 (2) ◽

pp. 117-137 ◽

Cited By ~ 5

Author(s):

A.K. Alva

Keyword(s):

Water Content ◽

Soil Water ◽

Real Time ◽

Soil Water Content ◽

Soil Profile ◽

Continuous Monitoring ◽

Sandy Soils

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Water Content Determination in Biodiesel: Optimization of Methodology in Coulometric Karl Fischer Titration

Biofuels ◽

10.1520/stp49342s ◽

2011 ◽

pp. 42-42-9

Author(s):

M. P. Vicentim ◽

M. V. Barreto Sousa ◽

V. Fernandes da Silva ◽

V. Lionel Mateus ◽

J. M. Rodrigues ◽

...

Keyword(s):

Water Content ◽

Karl Fischer Titration ◽

Karl Fischer ◽

Content Determination ◽

Coulometric Karl Fischer Titration

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Comparison of travel time analysis and inverse modeling for soil water content determination with time domain reflectometry

Water Resources Research ◽

10.1029/2001wr000259 ◽

2002 ◽

Vol 38 (6) ◽

pp. 13-1-13-8 ◽

Cited By ~ 27

Author(s):

J. A. Huisman ◽

A. H. Weerts ◽

T. J. Heimovaara ◽

W. Bouten

Keyword(s):

Water Content ◽

Travel Time ◽

Soil Water ◽

Soil Water Content ◽

Time Domain ◽

Inverse Modeling ◽

Time Domain Reflectometry ◽

Time Analysis ◽

Content Determination

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Development of calibration algorithms for selected water content reflectometry probes for burned and non-burned organic soils of Alaska

International Journal of Wildland Fire ◽

10.1071/wf07175 ◽

2010 ◽

Vol 19 (7) ◽

pp. 961 ◽

Cited By ~ 8

Author(s):

Laura L. Bourgeau-Chavez ◽

Gordon C. Garwood ◽

Kevin Riordan ◽

Benjamin W. Koziol ◽

James Slawski

Keyword(s):

Soil Moisture ◽

Moisture Content ◽

Water Content ◽

Soil Profile ◽

Soil Moisture Content ◽

Mineral Soil ◽

Organic Soil ◽

Organic Content ◽

Organic Soils ◽

Probe Type

Water content reflectometry is a method used by many commercial manufacturers of affordable sensors to electronically estimate soil moisture content. Field‐deployable and handheld water content reflectometry probes were used in a variety of organic soil‐profile types in Alaska. These probes were calibrated using 65 organic soil samples harvested from these burned and unburned, primarily moss‐dominated sites in the boreal forest. Probe output was compared with gravimetrically measured volumetric moisture content, to produce calibration algorithms for surface‐down‐inserted handheld probes in specific soil‐profile types, as well as field‐deployable horizontally inserted probes in specific organic soil horizons. General organic algorithms for each probe type were also developed. Calibrations are statistically compared to determine their suitability. The resulting calibrations showed good agreement with in situ validation and varied from the default mineral‐soil‐based calibrations by 20% or more. These results are of particular interest to researchers measuring soil moisture content with water content reflectometry probes in soils with high organic content.

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Modelling leaching and recharge in a bare transitional red-brown earth ponded with low salinity water in summer

Australian Journal of Experimental Agriculture ◽

10.1071/ea9941085 ◽

1994 ◽

Vol 34 (7) ◽

pp. 1085 ◽

Cited By ~ 1

Author(s):

L Cai ◽

SA Prathapar ◽

HG Beecher

Keyword(s):

Hydraulic Conductivity ◽

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Soil Profile ◽

Soil Surface ◽

Saturated Hydraulic Conductivity ◽

Rate Dependent ◽

Water And Salt Movement ◽

Winter Fallow

A modelling study was conducted to evaluate water and salt movement within a transitional red-brown earth with saline B horizon soil when such waters are used for ponding in summer. The model was calibrated using previously published experimental data. The calibrated model was used to evaluate the effect of depth to watertable, saturated hydraulic conductivity, and ponding water salinity on infiltration, water and salt movement within the soil profile, and recharge. The study showed that when initial soil water content and the saturated hydraulic conductivity (Ks) are low, infiltrating water will be stored within the soil profile even in the absence of a shallow watertable. Once the soil water content is high, however, recharge will be significant in winter, even if there is no net infiltration at the soil surface. Infiltration rates depend more on Ks than the depth to watertable if it is at, or below, 1.5 m from the soil surface. When Ks is high, recharge under ponding will be higher than that under winter fallow. Subsequent ponding in summer and fallow in winter tend to leach salts from the soil profile, the leaching rate dependent on Ks. During winter fallow, due to net evaporation, salts tend to move upwards and concentrate near the soil surface. In the presence of shallow watertables, leached salts tend to concentrate at, or near, the watertable.

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