A laboratory and glasshouse investigation on the effect of liming with fly ash and processed stainless steel slag on two contrasting South African soils.

Abstract

Soil acidity is a major land degradation problem that limits crop production globally. The high cost of traditional liming materials (calcitic limestone, dolomite etc.) and the vast areas of land that require liming have led to the exploratory utilisation of alkaline industrial by- products such as fly ash and stainless steel slag. The liming potential and effects of liming with fly ash (from the Duvha power station) and processed stainless steel slag (Calmasil) on two acid soils were investigated in this study. The quality of fly ash and Calmasil as liming materials and their potential impacts on the soil quality and plant growth were investigated. The effects of liming with these materials on soil pH, EC, extractable Al, Mn, base cations and trace elements were investigated in an incubation experiment. A glasshouse trial was conducted to assess the effects of these materials on the growth of an acid intolerant crop, perennial rye grass. The incubation and glasshouse study were of a factorial design with two acid soils (the Avalon and Inanda soils), three materials (fly ash, Calmasil and lime); and five application rates of 0, 50, 100, 200 and 400% of the recommended optimum liming rate (OLR) for the growth of perennial rye grass. Characterization of fly ash showed that the major elements (>5%) present (Si > Al > Fe) are not comparable to lime (Ca > Si > Mg) and that it has a low liming potential (calcium carbonate equivalence (CCE) of 9.6%) in comparison to lime. The chemical composition of Calmasil is comparable to lime with Ca > Si > Mg as the major elements and it has a very high liming potential (CCE = 97%). The incubation experiment showed that adding fly ash and Calmasil increased the pH of both soils. However, at the optimum liming rate (100% OLR), only the treatment with Calmasil in the Avalon soil attained pH levels within the desired pH range. Extractable Al and Mn decreased with addition of fly ash and Calmasil to levels comparable to lime in the incubated soils. Addition of fly ash and Calmasil also increased the extractable base cations of both soils. The yield-response of perennial rye grass to treatments in both soils was in the following order: fly ash > Calmasil > lime. Application of fly ash at > 200% OLR in the Avalon soil caused injury of ryegrass. Application of fly ash and Calmasil at lower rates has great agronomic potential in ameliorating soil acidity.