Published online by Cambridge University Press: 27 March 2009
1. The solubility of the phosphorus of soils and of other phosphatic materials in solutions of sodium hydroxide has been investigated. A method for the extraction and determination of the soluble phosphorus is described.
2. With acid soils, especially when the exchangeable calcium has been removed by leaching, an approximately constant amount of phosphorus is extracted by sodium hydroxide solution of strengths from 2 per cent to 20 per cent. The soda-soluble fraction amounts to 90 per cent of the total phosphorus.
3. Soils containing free calcium carbonate vary in the solubility of their phosphorus in sodium hydroxide solutions. Some behave similarly to acid soils, whilst others show only a small fraction of their total phosphorus to be soda-soluble. The extraction is complicated by the presence of calcium carbonate, which can precipitate from solution compounds which, in its absence, are soda-soluble.