Prediction of the dissolution of calcium sulphate containing soil amendments by a computer model
1995
Darab, K. | Csillag, J. (Hungarian Academy of Sciences, Research Institute for Soil Science and Agrochemistry, Budapest (Hungary))
In soils with an approximately same degree of sodium saturation but differing in the chemistry of their salinization, the quantities of dissolved calcium sulphate may vary to a great extent. Therefore, when predicting the amendment dose, the chemical composition of the soil solution cannot be neglected. A model - based on the equilibria of calcium sulphate dissolution - has been developed to compute the quantity of calcium sulphate dissolved in soil solutions or soil aqueous extracts, taking into account the influence of common and non-common ions on the solubility of amendments. In this model the soil solution is treated as a multicomponent electrolyte solution. The validity of the computerized model was proved by the good agreement between the computed and measured data obtained in aqueous salt solutions and soil saturation extracts saturated with calcium sulphate. A significant difference (on 5 level) was found between the calcium and sulphate ion concentrations measured in soil saturation extracts saturated with activated fine-grain anhydrite and the ones computed by the model when the thermodynamic solubility product of anhydrite published in the literature was applied. This means that the activity of the solid phase of this material is probably not a constant value and is not equal to one. Nevertheless, the model is suitable, even in its present state, to predict the solubility of calcium sulphate containing amendments in the soil solution
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