Spatial and temporal dynamics of air permeability in a constructed field

Soil air permeability in undisturbed soil is closely related to soil struct ure and heterogeneity and hydraulic properties. Knowledge of air permeabili ty behavior for different types of soils is, therefore, valuable. In this s tudy, we investigated the variability and spatial correlation structure of soil air permeability and soil textural properties in an undisturbed constr ucted field at Hiroshima University, Hiroshima, Japan. Air permeability was measured on undisturbed soil samples along two 70-m-long transects in the top 10 cm of a field constructed approximately 20 years ago from sandy loam soil collected from a nearby mountain. Air permeability (k(a)) showed spat ial correlation along both transects, with a range of approximately 20 in. Measurements of k(a) on large (3140 cm(3)) samples were similar, showing a soil with little small-scale heterogeneity. Local-scale measurements of k(a ) within a 1.6- by 1.6-m grid taken 4 months after the transect sampling su ggested that soil structure and pore size distribution had changed signific antly over time, as a result of tilling and precipitation, causing an incre ase in k(a). No spatial drift in soil physical parameters within the 1.6- b y 1.6-m grid was found. On-site k(a) measurements after 1- to 2-day rainy p eriods compared well with laboratory measurements at a soil-water potential of -100 cm H2O, suggesting that natural field capacity occurs at this pote ntial. Measurements of k(a) as a function of air-filled porosity (epsilon) at the mid-point of the two transects were compared with predictions by two recently presented k(a) (epsilon) models, and good agreement between simul ated values and measurements was found.