Unsaturated Hydraulic Conductivity: Laboratory Tension Infiltrometer

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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Unsaturated hydraulic conductivity of conventional and conservation tillage soils in southern Alberta

Canadian Journal of Soil Science ◽

10.4141/s97-061 ◽

1998 ◽

Vol 78 (4) ◽

pp. 643-648 ◽

Cited By ~ 15

Author(s):

J. J. Miller ◽

N. J. Sweetland ◽

F. J. Larney ◽

K. M. Volkmar

Keyword(s):

Hydraulic Conductivity ◽

Conservation Tillage ◽

Geometric Mean ◽

Conventional Tillage ◽

Canadian Prairies ◽

Tension Infiltrometer ◽

Unsaturated Hydraulic Conductivity ◽

Significant Difference ◽

Southern Alberta ◽

Nonlinear Regression Method

Conservation tillage is increasing on the Canadian prairies and its long-term effect on soil physical properties warrants investigation. Tension infiltrometer measurements were conducted on conventional tillage (CT), minimum tillage (MT) and no-till (NT) loam to clay loam soils in southern Alberta to determine if 26 yr of conservation tillage (MT, NT) modified the unsaturated hydraulic conductivity, K(ψ), relative to CT. Tillage of CT and MT plots was performed using a wide-blade cultivator. Measurements were performed on tillage treatments that were replicated on two adjacent parcels of land, with readings taken at the west parcel (Site 1) in 1993 and at the east parcel (Site 2) in 1994. Infiltration rates were determined at water potentials (ψ) of −0.3, −0.6 and −1.5 kPa. The K(ψ) values at −0.3, −0.6, −1.0 and −1.5 kPa (equivalent circular pore diameters of 1000, 500, 300 and 200 µm, respectively) were estimated from infiltration data using the nonlinear regression method of Logsdon and Jaynes. Tillage had a significant (P < 0.10) effect on K(ψ). Geometric mean K(ψ) values for NT (12.8 × 10−8 m s−1) were significantly (P < 0.05) lower than for CT (21.9 × 10−8 m s−1), but there was no significant difference between MT (13.6 × 10−8 m s−1) and CT, or between MT and NT. Although there was no significant tillage × site-year interaction (P > 0.10) for K(ψ), there was a trend for higher K(ψ) values at −0.6, −1.0 and −1.5 kPa in CT than MT and NT for Site 1 in 1993 compared to Site 2 in 1994. This trend was consistent with a shorter lag time between the most recent tillage event and subsequent infiltration measurements in CT for Site 1 in 1993 (1–16 d) compared with Site 2 in 1994 (28–45 d). Key words: Tillage, tension infiltrometer, unsaturated hydraulic conductivity

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Modified tension infiltrometer and its use to determine the unsaturated hydraulic conductivity of upper vadose zone

Journal of Nepal Geological Society ◽

10.3126/jngs.v18i0.32258 ◽

1998 ◽

Vol 18 ◽

Author(s):

Golam Shabbir Sattar

Keyword(s):

Steady State ◽

Hydraulic Conductivity ◽

Vadose Zone ◽

Water Pressure ◽

Fundamental Property ◽

Pressure Head ◽

Unknown Parameters ◽

Steady State Condition ◽

Tension Infiltrometer ◽

Unsaturated Hydraulic Conductivity

A modification of the CSIRO type tension infiltrometer was designed (designated UNCEL type) and tested. This infiltrometer is considerably cheaper, but more versatile, than any other infiltrometer reported so far. The modified infiltrometer was used in a reconstructed vadose zone to measure the unsaturated hydraulic conductivity and effect of compaction associated with the upper vadose zone. Hydraulic conductivity, a function of matric potential, is a fundamental property for water entry into the soil as well as in the upper vadose zone. Tension infiltrometer technique for determining unsaturated hydraulic conductivity, which is also a function of soil water pressure head, was compared with the existing techniques. The analysis of data from tension infiltrometer is based mainly on flow rate at steady-state condition. The steady-state measurement also enables to determine unknown parameters on the basis of at least two negative heads at the same location. This modified infiltrometer imposes pressure potentials at soil surface from 0.01 to 0.15 m of water, as a result macropores with an air entry value of less than applied tension are excluded. This is practically useful when investigating the influence of structure and compaction of upper vadose zone. Measurement of infiltration at various negative pressure head, with a single disc diameter allowed sensitive measurement of hydraulic properties of upper vadose zone with minimal surface disturbance. The newly designed tension infiltrometer and adopted schemes of calculation enable to determine unsaturated hydraulic conductivity of upper vadose zone with relevance to structural effects more accurately.

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