Hydraulic conductivity in a clay soil: Two measurement techniques and spatial characterization

Infiltration, drainage, and chemical leaching are strongly influenced by the magnitude and spatial distribution of the field-saturated soil hydraulic conductivity (K-fs). The Guelph permeameter (GP) method shows promise as an effective means for held measurement of K-fs 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 K-fs 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 K-fs at this field site, and that the GP method is capable of providing valid estimates of K-fs in at least some fine-textured soils. The K-fs 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 (theta(a)) measured in situ prior to the GP measurements using a down-hole time domain reflectometry probe. The semivariogram for theta(a) was similar to those for K-fs. These results suggest that the magnitude, range, and pattern of variability of the K-fs 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.