THE USE OF A SIMPLE FIELD AIR PERMEAMETER AS A RAPID INDICATOR OF FUNCTIONAL SOIL PORE-SPACE

Currently there is a lack of quantitative data on the functional class ification of soil structure, particularly in routine soil surveys, bec ause field physical measurements of flow characteristics are slow and require expertise. A simple air permeameter was developed which allows rapid, in situ measurements to be made of the intrinsic permeability of the soil to air (k(a)). Measurements of k(a) are highly dependent o n the structure of the soil, in particular the size and continuity of macropores, and therefore can be used as an estimate of functional por e space (pore space contributing to the transmission of air and water) in the soil. Values of k(a) ranged from 5.6 mum2 for a compacted allu vial soil under pasture to 276.8 mum2 for a red-brown earth under nati ve grass, cultivated one year before the time of measurement. Developm ent of a functional pore space scoring table for use in the field has shown that k(a)0.5 can be estimated from morphological descriptions of the soil. However, field descriptions are qualitative, subjective and difficult to apply consistently. The air permeameter can discriminate between the structural differences in soil under different management practices. The air permeameter should appeal to pedologists who wish to have a quantitative aid in the interpretation of soil structure.