A Model of the Extent of Anaerobic Zones in Aggregated Soils, and Its Potential Application to Estimates of Denitrification 1

Summary A model has been developed of the variation in the extent of anaerobiosis in aggregated soils with variations in gaseous diffusion coefficients, respiration rate and aggregate size. It extends previously published models of radial diffusion into individual aggregates to a log‐normally distributed population of aggregate sizes such as is known to occur in the field. It considers in particular the situation in which relatively better drainage and aeration occurs in the inter‐aggregate pores than within the aggregates. The model indicates that in most circumstances the effects of variations in the gaseous diffusion coefficients outweigh comparable variations in aggregate size. It is demonstrated how the model may be applied to calculation of rates of denitrification, and two alternative approaches are proposed: one based on the quantities of nitrogen and nitrous oxide diffusing out of partially anaerobic aggregates, the other on the disappearance of nitrate following diffusion into anaerobic zones.