SOIL AERATION

Abstract

Recent models of gaseous diffusion in soils have taken account of the effects of soil structure, and explain the development of anaerobic zones within aggregates. Aggregate sizes commonly fit log-normal distribution. In clayey soils anaerobic conditions persist for long periods in the larger aggregates, but quantitative assessment of anaerobic volumes is complicated by uncertainty about the value of the diffusion coefficient for oxygen in wet soils.

Methods of measuring soil aeration, and the results of field studies, are reviewed. It is concluded that climatic factors have more effect than cultivation or compaction, and drainage produces little improvement in the heaviest soils. Under these conditions considerable losses of nitrogen occur by denitrification, and significant concentrations of physiologically active compounds such as ethylene are released.