Hydraulic Conductivity in a Clay Soil: Two Measurement Techniques and Spatial Characterization

Abstract

Infiltration, drainage, and chemical leaching are strongly influenced by the magnitude and spatial distribution of the field‐saturated soil hydraulic conductivity (Kfs). The Guelph permeameter (GP) method shows promise as an effective means for field measurement of Kfs and its spatial distribution, but its accuracy in medium‐ and fine‐textured soils is not well established. To further assess its accuracy and effectiveness, the GP method was compared with the auger hole (AH) method at the 0.5‐m depth at 68 grid locations in a texturally uniform silty clay soil that had stable but spatially variable structure. The two methods yielded similar geometric mean Kfs values (P < 0.001), as well as similar semivariograms. The two methods were also positively correlated (r = + 0.6565, P < 0.0001). We therefore concluded that the two methods gave equivalent estimates of Kfs at this field site, and that the GP method is capable of providing valid estimates of Kfs in at least some fine‐textured soils. The Kfs values were not correlated with soil texture, organic C content, or soil surface topography, but were negatively correlated (r = −0.7240 for GP method, r = −0.6070 for AH method, P < 0.0001) with antecedent volumetric water content (θa) measured in situ prior to the GP measurements using a down‐hole time domain reflectometry probe. The semivariogram for θa was similar to those for Kfs. These results suggest that the magnitude, range, and pattern of variability of the Kfs measurements were controlled primarily by the well‐developed and stable soil structure at the field site, rather than by texture, organic C content, or surface topography.

Spatial and temporal variability of soil saturated hydraulic conductivity in gradients of disturbance

“…Existing spatial structure is attributed to a well-developed and stable soil structure (Reynolds and Zebchuk, 1996), uniform texture and pore size distribution developed by long-term (notillage) agricultural practice (Mohanty and Mousli, 2000), or intrinsic variations in soil texture and mineralogy (Shukla et al, 2004). The absence of spatial predictability is assumed to be caused by biogenic macroporosity, which overrides possible texture and topography dependence (Sobieraj et al, 2002), uneven breaking of soil structure due to freezing and thawing (Mohanty et al, 1991), or surface tillage in the upper horizons (Bosch and West, 1998).…”

“…There are some indications, however, that a predictable spatial structure might be associated with stable soil conditions (Reynolds and Zebchuk, 1996, Mohanty and Mousli, 2000, Shukla, 2004. In contrast, a spatially independent random variation seems to originate from processes that interrupt the spatially-dependent intrinsic variations as e.g.…”

Effect of tillage and water pressure head on the hydraulic properties of a loamy soil surface

“…One of the biggest problems in determining the hydraulic conductivity of cultivated soils is its sensitivity to changes in soil structure; great care must be taken to minimise alterations in soil structure when taking measurements (Vieira et al, 1981;Wilson and Luxmoore, 1988;Reynolds and Zebchuk, 1996;Bosch and West, 1998;Zavattaro et al, 1999). Further, in modelling water transport through unsaturated soils, it is assumed that the characteristics of the soil remain temporally invariant, which can lead to discrepancies between expected and observed results.…”

“…Although all measuring procedures are affected by soil heterogeneity to varying extents, those that employ multiple infiltrometers of different radius (Smettem and Clothier, 1989) and those requiring analyses based on the combined transient steady state flow (White et al, 1992) appear to be the most susceptible. In addition, good and consistent hydraulic contact between the infiltrometer membrane and the soil must be maintained at all times if reliable results are to be obtained (Reynolds and Zebchuk, 1996). This is best achieved by placing a layer of contact sand between the infiltrometer membrane and the soil surface.…”

Variabilidade dos parâmetros da equação da condutividade hidráulica em função da umidade de um latossolo sob condições de campo.

“…Neste sentido Reynolds & Zebchuk (1996) Como se trata de um meio naturalmente descontínuo, o conceito de homogeneidade para os solos e suas características tem uma aplicação relativa e depende, portanto, da escala de observação ( Seyfried, 1998). Por isso, estabeleceu-se que a quantificação da variabilidade de um certo atributo medido neste corpo geológico deve ser feita por meio de técnicas estatísticas (Grossi Sad, 1986).…”