Thixotropic Changes in the Stability of Molded Soil Aggregates

Abstract

Abstract Thixotropic age hardening of clays has long been familiar to civil engineers but its contribution to the stabilization of aggregates produced by cultivation has been little studied. We report changes in stability after simulated cultivation of soil samples from arable and pasture fields. The contribution of biological processes to stabilization was eliminated by sterilization and the effects of the “polysaccharide” fraction of the soil organic matter were removed by periodate oxidation. Thixotropic changes were shown to make a contribution to the age hardening process in both molded and remolded soil aggregates similar in magnitude to the contribution made by biological processes. These changes were reversible and accompanied by soil matric water potential changes. Destruction of the polysaccharide fraction of soil organic matter reduced aggregate stability and removed most of the differences between arable and pasture soils of the same series, but polysaccharides do not appear to contribute to the thixotropic aging process.