THE EFFECT OF SOIL COMPOSITION AND ENVIRONMENTAL FACTORS ON THE SHRINKAGE OF SOME CLAYEY BRITISH SOILS

The shrinkage potential of natural clods from a variety of clayey soils was measured and related to their physical, chemical and mineralogical properties. It is shown that the most important factors affecting shrinkage are initial bulk density, clay content, organic carbon content and cation exchange capacity of the peroxidised clay, and mica-smectite content on a whole soil basis. Multiple regression equations involving the initial bulk density, clay content, organic carbon and cation exchange capacity accounted for 87 and 82 per cent of the variation in total shrinkage of topsoils and subsoils respectively. Because of restrictions on shrinkage imposed by factors such as climate, crops, ground-water and moisture release characteristics of soils, soils with a high shrinkage potential may not behave very differently to soils with a much lower potential. On these grounds it is concluded that the shrinkage criteria used in US Taxonomy are not applicable in Britain.