Calcined Christmas Island C-grade rock phosphate fertilizers: Mineralogical properties, reversion and assessment by chemical extraction
- 1 January 1979
- journal article
- research article
- Published by CSIRO Publishing in Soil Research
- Vol. 17 (3) , 467-481
- https://doi.org/10.1071/sr9790467
Abstract
Calcination of Christmas Island C-grade ore at temperatures up to 1050.degree. C produces P fertilizers that differ greatly in effectiveness as determined by citrate extraction and plant growth. Maximum effectiveness is obtained by calcination at temperatures between 500.degree. and 650.degree. C, and is best predicted by extractions of between 1 and 3 h duration in neutral ammonium citrate. Alkaline ammonium citrate and citric acid are poorer indicators of phosphorus availability. The mineralogical and chemical properties of the calcines may be used to explain variations in amounts of citrate soluble P for different temperatures of calcination. Incubation of moist 500.degree. C calcined C-grade ore induces recrystallization (i.e., reversion) of some crandallite, resulting in a decrease in the solubility of P in neutral ammonium citrate and its availability to plants.Keywords
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