Modification of soil physical properties by addition of calcium compounds

Abstract

In a soil to which gypsum, calcium carbonate or cement was added, the content of dispersible clay was related to both exchangeable sodium percentage (ESP) and electrical conductivity (EC). The electrolyte concentration in the soil which could be maintained by addition of calcium carbonate was such that an ESP of >3 was required to maintain clay coagulation. Small amounts of gypsum (0.2% w/w) coagulated most of the clay by lowering the ESP and raising the electrolyte concentration. However, the clay gradually dispersed as the soil was subjected to wetting and drying cycles and the electrolyte concentration was decreased. The most efficient use of gypsum would appear to be as small annual additions. The addition of cement resulted in the stabilization of particles 250-2000 µm diameter, i.e. cementation as opposed to coagulation. Both processes resulted in changes to various physical properties and mechanical properties of the soil. It is suggested that both coagulation and cementation in a soil may be achieved by the addition of gypsum and cement or lime, with significant improvements of soil structure. In soils with gypsum added the germination and total yield of dry matter of wheat were improved significantly, but the opposite trend was recorded for soils treated with cement.