Measuring unsaturated hydraulic conductivity (K(ψm)) of the F and H soil organic layers at small matric potential (ψm)

Wilske, B. and Johnson, E. A. 2011. Measuring unsaturated hydraulic conductivity (K(ψm)) of the F and H soil organic layers at small matric potential (ψm). Can. J. Soil Sci. 91: 965–968. K(ψm) of the soil organic layers is a key parameter to assess water redistribution in cold-climate forests. This study tested the twin suction disc apparatus (TSD) as a new method to measure K(ψm) of the F and H layers directly. We compared the results to two studies. One represents a large data base, the other used similar sample locations; but both derived K(ψm) from combining two methods, i.e., pressure plate measurements combined with the instantaneous profile technique or the constant head approach. The TSD data are consistent with previous results considering the large variability in K(ψm) from the combined methods. This suggests that the TSD method represents an alternative to determine K(ψm) of the soil organic layer.

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Physical properties of the mor layer in a Scots pine stand I. Hydraulic conductivity

Canadian Journal of Soil Science ◽

10.4141/s95-002 ◽

1997 ◽

Vol 77 (4) ◽

pp. 627-634 ◽

Cited By ~ 16

Author(s):

A. Laurén ◽

J. Heiskanen

Keyword(s):

Hydraulic Conductivity ◽

Pinus Sylvestris ◽

Scots Pine ◽

Hydraulic Properties ◽

Matric Potential ◽

Unsaturated Hydraulic Conductivity ◽

Undisturbed Samples ◽

Constant Head ◽

Humified Peat ◽

Properties Of Soil

Hydraulic conductivity in the mor layer of a Scots pine (Pinus sylvestris L.) stand was measured in undisturbed samples using the constant-head permeameter and instantaneous-profile method. Saturated hydraulic conductivity (Ks) averaged 2.9 × 102 m d−1. With a decrease in matric potential (ψ) from −4 kPa to −70 kPa the unsaturated hydraulic conductivity (K(ψ)) decreased from 3.1 × 10−3 to 1.1 × 10−8 m d−1. Ks and K(ψ) were similar to those reported in the literature for low-humified peat. The variation in hydraulic conductivity within a stand of Scots pine at a given matric potential was large, ranging from one to two orders of magnitude. Key words: F horizon, humus, hydraulic properties of soil

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Measurement of unsaturated hydraulic conductivity using tension and drip infiltrometers

Soil Research ◽

10.1071/sr99136 ◽

2001 ◽

Vol 39 (4) ◽

pp. 823 ◽

Cited By ~ 9

Author(s):

N. J. McKenzie ◽

H. P. Cresswell ◽

H. Rath ◽

D. Jacquier

Keyword(s):

Hydraulic Conductivity ◽

Soil Cores ◽

Matric Potential ◽

Constant Flux ◽

Tension Infiltrometer ◽

Unsaturated Hydraulic Conductivity ◽

Wide Range ◽

Constant Potential ◽

Potential Methods ◽

Large Decline

We investigated differences between constant flux and constant potential methods for determining unsaturated hydraulic conductivity in the laboratory. A cheap and robust method was required. The constant flux drip infiltrometer has been used with large intact cores on a wide range of Australian soils. However, the method can be simplified by replacing the drip infiltrometer with a constant potential tension infiltrometer (disc permeameter). We conducted a series of measurements using 9 soil cores to determine whether the measured hydraulic conductivity differed with each method at matric potentials of –10, –20, or –50 mm. Hysteresis effects were also examined because tension infiltrometer measurements are usually made on the adsorption curve of the hydraulic conductivity and matric potential [K(Ψ)] relationship. Drip infiltrometer measurements are often made on the desorption curve. The reproducibility of measurements on a single core was also examined. A large decline in K(Ψ ) was observed on some cores with repeated measurements and this effect was larger than differences between the methods. In the absence of evidence of slaking or dispersion, the suspected cause of the decline in K(Ψ) was clogging of pores from accumulation of microbial biomass and their by-products. The results support the view that K(Ψ) in some soils is a dynamic property. There were consistent differences between the constant flux and constant potential methods on those soil cores not exhibiting a large decline in K(Ψ) (the others were omitted from the method comparison). The tension infiltrometer method indicated greater hydraulic conductivity in soils with well-developed macrostructure when matric potential was greater than –50 mm. Hysteresis effects were significant with both methods and measurements made on desorption and adsorption curves are not considered comparable. Overall, we concluded that the tension infiltrometer method was more suited than the drip method for routine processing of large numbers of samples at low cost.

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A sensitivity analysis of the Jackson method of predicting unsaturated hydraulic conductivity

Soil Research ◽

10.1071/sr9920285 ◽

1992 ◽

Vol 30 (3) ◽

pp. 285 ◽

Cited By ~ 1

Author(s):

HP Cresswell

Keyword(s):

Sensitivity Analysis ◽

Hydraulic Conductivity ◽

Water Content ◽

Volumetric Water Content ◽

Small Range ◽

Matric Potential ◽

Unsaturated Hydraulic Conductivity ◽

Moisture Characteristic ◽

Intended Use ◽

Water Contents

An assessment is made of the sensitivity of the unsaturated hydraulic conductivity predictions from the Jackson model to changes in the measured moisture characteristic and matching factor hydraulic conductivity inputs. The model is shown to be sensitive to the volumetric water content corresponding to the matching factor hydraulic conductivity as well as to the 0 to -1.0 kPa matric potential section of the moisture characteristic input. The significance of this sensitivity is dependent on intended use of the data. Where accurate conductivity prediction is required over a small range of water contents near saturation, the moisture characteristic input used with this model should include measured points between 0 and 1.0 kPa matric potential.

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