Field Application of a Portable Air Permeameter to Characterize Spatial Variability in Air and Water Permeability
2003
Iversen, Bo V. | Moldrup, Per | Schjønning, P. (Per) | Jacobsen, Ole H.
The saturated hydraulic conductivity (K ₛ) is an essential parameter for modeling water and chemical transport in the vadose zone. Since in situ measurements of K ₛ are complex and time-consuming, indirect methods that are dependable, fast, and inexpensive with regard to assessing magnitude and spatial variability in K ₛ at the field scale are needed. In situ measurements of air permeability (k ₐ,ᵢₙ ₛᵢₜᵤ) may fulfill these criteria. In this study, a portable insertion-type air permeameter was used to measure k ₐ,ᵢₙ ₛᵢₜᵤ in the Ap and B horizons at five agricultural field sites in Denmark with soil types ranging from sand to sandy loam. Around 100 k ₐ,ᵢₙ ₛᵢₜᵤ measurements were performed within 2 d at each field site. The data showed spatial correlation in k ₐ,ᵢₙ ₛᵢₜᵤ at three out of five sites, with correlation distances between 30 and >120 m. On the basis of additional laboratory measurements on large, undisturbed soil samples (6280 cm³), a log-log linear relationship between air permeability (k ₐ) measured at the actual soil-water content (close to field capacity) and K ₛ was found. The K ₛ–k ₐ relation was in agreement with an earlier predictive relationship based on undisturbed 100-cm³ samples from nine other field sites. Using pedotransfer functions for K ₛ based only on soil texture yielded an unrealistic narrow range in predicted K ₛ values whereas pedotransfer functions based on k ₐ,ᵢₙ ₛᵢₜᵤ yielded a more realistic prediction range. Measurements of k ₐ,ᵢₙ ₛᵢₜᵤ constitute a promising indirect method for assessing spatial variability in K ₛ at the field scale.
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