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Title: Apparent electrical conductivity (ECa) as a surrogate for neutron probe counts to measure soil moisture content in heavy clay soils (Vertosols)
Contributor(s): Stanley, John (author); Lamb, David (author); Falzon, Gregory (author)orcid ; Schneider, Derek (author)orcid 
Publication Date: 2014
DOI: 10.1071/SR13142
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Abstract: Site-specific measurements of the apparent electrical conductivity (ECa) of soil using the EM38 were correlated with near-simultaneous neutron probe readings over periods of moisture extraction by an irrigated cotton crop. Thirty sites were monitored from three ECa zones within a 96-ha field of grey Vertosol soil 30 km west of Moree, New South Wales, Australia. This study differs from previous approaches by reporting the effect on ECa of a wetting front (irrigation) reaching a single ECa measurement point in a field and by using polyethylene neutron probe access tubes so that the EM38 could be operated directly over the same site measured by a neutron probe. We report strong correlations (r = 0.94) between neutron probe counts (CRR) averaged to a depth of 40 or 60 cm and ECa from an EM38 held in the vertical mode 20 cm above the soil surface. All combinations of EM sensor height (0-1.2 m) to neutron probe measurement depth (0.2-1.4 m) returned correlations >0.85. The relationship between CCR and ECa was linear for the purposes of estimating water content over a range of background ECa levels. More critical modelling suggested a slight curve (logarithmic model) fitted best. The range of surface-surveyed ECa from the start of irrigation (refill point) to fully irrigated (full point) was ~27mSm⁻¹ for this Vertosol, where surface ECa readings typically ranged from 50 to 200mSm⁻¹. We suggest that the calibration of ECa to CRR might be effected by a two-point measurement of the soil, namely at both upper (field capacity) and lower (wilting point) ECa values, and a site-specific calibration template generated by extending these point measures to whole-field surveys.
Publication Type: Journal Article
Source of Publication: Soil Research, 52(4), p. 373-378
Publisher: CSIRO Publishing
Place of Publication: Australia
ISSN: 1838-675X
Field of Research (FOR): 070104 Agricultural Spatial Analysis and Modelling
040401 Electrical and Electromagnetic Methods in Geophysics
Peer Reviewed: Yes
HERDC Category Description: C1 Refereed Article in a Scholarly Journal
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Appears in Collections:Journal Article
School of Environmental and Rural Science

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