Phosphate Analysis

Organic farming methods may permit the application of natural rock phosphate, but not superphosphates. The former releases phosphate more slowly, therefore the extractant must be carefully chosen to reflect this fact. The acid Bray and Truog methods will extract too much phosphate to give spuriously high readings, whereas the alkaline extractants will extract very little. Preliminary tests indicate that the resin-extractable P method seems to give results which closely reflect the crop performance whether superphosphate or reactive phosphate rocks are used, and a discussion on the subject is given by Agricultural Consulting Services, Technical Services, at:

http://www.atsnet.co.nz/articles/resinp.htm The Hislop and Cooke (1968) and Somasire and Edwards (1992) resin P methods are discussed in Chapter 4, and an automated method is given in 5.9c. 'Determination of resin extractable phosphorus (automated method)'.

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