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SPECIAL SECTION - ADVANCES IN MEASUREMENT AND MONITORING METHODS

Field Application of a Portable Air Permeameter to Characterize Spatial Variability in Air and Water Permeability

^a Danish Institute of Agricultural Sciences, Dep. of Agroecology, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark
^b Environmental Engineering Section, Dep. of Life Sciences, Aalborg University, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark
^* Corresponding author (bo.v.iversen{at}agrsci.dk).

Received 18 March 2003.

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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