A method to prevent edge-flow in undisturbed soil cores and lysimeters

This study shows that edge-flow of water and solutes between soil samples and lysimeter or permeameter casings can result in significant errors in the measurement of hydraulic conductivity and leaching rates. A new lysimeter design and technique are described which prevent edge-flow from occurring. Liquefied petrolatum is injected into an annular gap between the soil and the lysimeter casing producing a watertight seal. Water and solute movement in the sealed lysimeter is therefore confined within the soil monolith and no edge-flow occurs. Hydraulic conductivity and solute leaching rates are significantly lower in sealed lysimeters compared with unsealed ones.

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Estimating the van Genuchten retention curve parameters of undisturbed soil from a single upward infiltration measurement

Soil Research ◽

10.1071/sr16333 ◽

2017 ◽

Vol 55 (7) ◽

pp. 682 ◽

Cited By ~ 3

Author(s):

D. Moret-Fernández ◽

C. Peña-Sancho ◽

B. Latorre ◽

Y. Pueyo ◽

M. V. López

Keyword(s):

Water Retention ◽

Time Domain Reflectometry ◽

Soil Samples ◽

Water Retention Curve ◽

Internal Diameter ◽

Soil Cores ◽

Undisturbed Soil ◽

Retention Curve ◽

Loam Soil ◽

Undisturbed Soil Cores

Estimation of the soil–water retention curve, θ(h), on undisturbed soil samples is of paramount importance to characterise the hydraulic behaviour of soils. Although a method of determining parameters of the water retention curve (α, a scale parameter inversely proportional to mean pore diameter and n, a measure of pore size distribution) from saturated hydraulic conductivity (Ks), sorptivity (S) and the β parameter, using S and β calculated from the inverse analysis of upward infiltration (UI) has been satisfactorily applied to sieved soil samples, its applicability to undisturbed soils has not been tested. The aim of the present study was to show that the method can be applied to undisturbed soil cores representing a range of textures and structures. Undisturbed soil cores were collected using stainless steel cylinders (5cm internal diameter×5cm high) from structured soils located in two different places: (1) an agricultural loam soil under conventional, reduced and no tillage systems; and (2) a loam soil under grazed and ungrazed natural shrubland. The α and n values estimated for the different soils using the UI method were compared with those calculated using time domain reflectometry (TDR) pressure cells (PC) for pressure heads of –0.5, –1.5, –3, –5, –10 and –50kPa. To compare the two methods, α values measured with UI were calculated to the drying branch of θ(h). For each treatment, three replicates of UI and PC calculations were performed. The results showed that the 5-cm high cylinders used in all experiments provided accurate estimates of S and β. Overall, the α and n values estimated with UI were larger than those measured with PC. These differences could be attributed, in part, to limitations of the PC method. On average, the n values calculated from the optimised S and β data were 5% larger than those obtained with PC. A relationship with a slope close to 1 fitted the n values estimated using both methods (nPC=0.73 nUI+0.49; R2=0.78, P<0.05). The results show that the UI method is a promising technique to estimate the hydraulic properties of undisturbed soil samples.

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