Field application of a portable air permeameter to characterize spatial variability in air and water permeability
2003
Iversen, B.V. | Moldrup, P. | Schjonning, P. | Jacobsen, O.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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