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The measurement of soil air permeability is a fast and easy method that can be used in different ways to characterize the soil. An air permeameter was constructed in order to measure air permeability (k a) in situ, on-site (exhumed soil samples), and in the laboratory on a wide range of Danish agricultural soils. Two different sizes of sample rings were used (100 cm 3 and 3140 cm 3). The device was initially tested in the laboratory on repacked soil samples to evaluate dependency of k a on sample size. The results showed consistent values of k a for both sample sizes, indicating only little scale effect. In the field, air permeability was measured in situ and on-site using large sample rings. Air permeability in situ was determined by using a" shape factor" taking into account boundary conditions at the lower end of the ring while assuming isotropic soil conditions. An expression for the shape factor developed by Liang et al …