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Hawke's Bay Tribune, Volume XXI, Issue 280, 10 November 1931, Page 11

The world’s fertiliser industry is dependent on three classes of material for its phosphate supply. These are, in the order of their importance, phosphate rock, basic slag and bone. Tho last-named is of minor importance because of the comparatively small quantity available for fertiliser use. The second, although limited by the production of steel, of which it is a byproduct, is available in great quantity. The first is available in practically unlimited quantity, and the deposits are widely distributed throughout the world. In preparing basic slag and bone for use as a fertiliser they may bo simply pulverised to a powder or meal. A similar treatment of phosphate rock yields a product W’hich is only slowly available as plant food. For this reason most of the phosphate rock is processed to increase its solubility, and there have been many methods suggested for tho treatment of this raw material.