South Africa has an abundance of agricultural lime sources distributed throughout the country which should enable farmers to source lime as economically as possible. Lime is classified as a Group 2 fertilizer and regulated by The Fertilizer, Farm Feeds and Agricultural Remedies Act of 1947 (Act 36 of 1947). Dolomitic and calcitic lime sources are used to ameliorate soil acidity, Al3+ and Mn2+ toxicities, raise soil pH and manage calcium and magnesium levels in the soil. The sources of lime may be of both natural and industrial origin and vary significantly in their chemical and physical properties which in turn will determine the efficacy the product being used. Factors affecting efficacy of lime In the article, Soil Acidity and its Management in Crop and Pasture Production; Miles and Farina indicate that the effectiveness of various liming materials varies widely, with the following factors being of particular importance: Chemical purity ─ the presence or otherwise of non-reactive materials such as sand and clay greatly affects the neutralizing value of the lime (importantly, the colour of the liming material is not a reliable indicator of its quality!). Chemical composition ─ the nature of the calcium and magnesium compounds present. Fineness ─ the finer the lime particles, the faster will be their reaction in the soil. Lime particles larger than 0.84 mm in diameter (about the size of a match head) are of little value. Very coarse liming materials are completely ineffective. Hardness ─ the solubility, and hence neutralizing value, of lime depends on whether it is derived from hard crystalline material or from softer relatively unconsolidated material. Where uncertainty exists as to the quality of a particular liming material, they advise that a sample should be submitted for analysis. The rate of chemical reaction When lime is applied to the soil it reacts with the acidic components of the soil, H+, Al3+ and Mn2+ , the rate of chemical reaction is determined by temperature, surface area for reaction, relative concentration of the reactants and the presence of soil moisture. Four factors determine the efficiency of lime: Rate of application Purity (CCE) Particle size distribution Degree of incorporation into soil Chemical purity – Calcium Carbonate Equivalent (CCE) The chemical composition of lime varies according to its geological or industrial origin. The term calcium carbonate equivalent (CCE) is a measure used to distinguish the neutralizing capacity of a lime source relative to the mass of pure calcium carbonate required to neutralize hydrochloric acid (HCl). The CCE of pure calcium carbonate is rated as 100%, pure magnesium carbonate has a lower molecular mass and as such less magnesium carbonate is required to neutralize the equivalent amount of HCl, the CCE of magnesium carbonate is 119%. The CCE of lime will vary according to the calcium (Ca) and magnesium (Mg) content as well as other impurities such as sand and clay; large variances in CCE may exist between different sources of lime. The minimum CCE of lime in terms of Act 36 is 70%. Fineness –…
Recent Comments