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The forgotten nutrient


By LIME & LIMING PRODUCTS, Soil Acidity, Sulphur No Comments

Gypsum (CaSO4.2H2O) and its dehydrated forms are relatively common minerals that are distributed worldwide in sedimentary and evaporative deposits and produced as bye products of various industrial processes. The main sources of gypsum are from the production of phosphoric acid from rock phosphate; gypsum produced from this process is a finely grained high purity material and is commonly referred to as phosphogypsum (PG). The main sources of PG in South Africa are located in Modderfontein, Phokeng, Potchefstroom and Phalaborwa which are reported to carry in excess of 15 million tons. Other sources of gypsum are produced from flue gas desulphurization (FGD) in industrial processes in which Sulphur Dioxide (SO2) is scrubbed to meet SO2 emission standards. There are numerous deposits of natural gypsum in the Cape which are mined. Natural gypsum tends to have a larger particle size distribution than gypsum produced from industrial processes unless it is milled finely. The effect of particle size is an important factor in determining the effectiveness of gypsum amendments. Gypsum is slightly soluble in aqueous solution, dissolving to an extent of 2.5 g / l. Natural gypsum may contain traces of calcium carbonate and therefore may reflect slightly alkaline pH levels on analysis, while PG may contain free acid which may reflect as slightly acidic on analysis. Overall Gypsum has very little effect on soil pH. South African agriculture utilizes approximately 200 000 tons of gypsum per year which with an approximate 18% Sulphur (S) content provides a cost effective source of S. Disclaimer: The figures published are not a guarantee of analysis, they are sourced from published Product Data Sheets and provided to serve as an indicator of typical analysis which may vary due to industrial impurities and changes in minerology of the natural sources. Please note: Consult a qualified person (Act 36 of 1947) for specific applications / recommendations

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