Self mulching behavior in clay soils - Its definition and measurement

Abstract

The history of the self-mulching concept is reviewed and from this a definition is proposed. Observation of the phenomenon to date has been quite subjective and qualitative, and the causes and mechanisms are little understood. A numerical index is developed to help redress these deficiencies. The self-mulching property embodies the ability of a soil to re-aggregate its clay in the course of wetting and air drying after the natural structure has been disrupted by puddling. A comparison of the clay released by such puddling with the clay released by shaking after drying and slaking of the puddle, forms the basis of the components for the numerical index. Suitable parameters for these components were extracted from experiments using typical Australian self-mulching soils. These soils also displayed a degree of subplasticity in at least part of their aggregated clay fraction. The numerical index values were compared with field structure ratings, made by pedologists, for 47 (mostly surface) soils from Australia and other parts of the world, and good agreement was found. The index is relevant to further work on mechanisms and modifications in self-mulching or potentially self-mulching soils.