Mar. 2, 1920.] Agricultural Gazette of N.SA'V. 181 



Phosphatic Fertilisers. 



The chief fertilisers supplying phosphorus are superphosphate (17 per cent. 



jphosphoric acid, water soluble) and bonedust (22 per cent., not water soluble). 



The water solubility of superphosphate ensures the immediate availability 



•of part of the phosphorus, and is evidenced by the stimulus (especially to 



Toot development) given to the young maize seedlings in almost every case 



where this fertiliser is applied with the seed. Much of this soluble phosphat« 



:soon becomes reverted to an insoluble form in the soil, but in such a fine 



:state of mechanical division that it is still considered readily available for the 



use of the plant. Bonedust is, however, quite insoluble until decomposed, 



and is likely to be of most value as a fertiliser for maize where decomposition 



takes place most readily, that is, in the presence of heat and moisture (for 



-example, chiefly in the coastal districts). Striking success has followed the 



application of a mixture of equal parts of su2)erphosphate and bonedust for 



maize (and for potatoes) on the coastal alluvial and volcanic soils. It may be 



that the superphosphate supplies the essential phosphorus to the young plant, 



and that part of the plant food of the bonedust is available to the plant at 



its later and more critical stages of growth, and during the filling of the cob. 



Perhaps, too, superphosphate acts on the bonedust in some way, and renders 



its phosphorus more quickly available. Whatever the cause, no fertiliser 



mixture yet tried has given such almost unexpectedly successful results 



as those obtained by this simple mixture on the coast during the last few 



years. 



It has been said that phosphorus is the limiting element in the production 

 of crops in Australia, because of the natural deficiency in most soils and also 

 •on account of the fact that in systems of grain farming this element is most 

 largelv removed in the grain, while the only source of replenishment is the 

 artificial fertiliser. This is just as true in relation to maize-growing on our 

 .soils, except that the loss from the farm of the phosphorus may be minimised 

 to a greater extent on account of maize being such an excellent food for 

 stock of all kinds and of the greater profits generally obtainable from the use 

 of the crop in this way. 



Even so, it has already been shown that animal manure is deficient in 

 phosphorus as compared with nitrogen and potash, and the utilisation of grain 

 for feeding stock on the farm can only defer somewhat the need for this 

 element from outside sources, such as fertilisers. It is withal the cheapest 

 element to buy, and one which usually yields a high percentage return on 

 the investment. In systems of green manuring — especially on less fertile 

 :goil — it usually causes a greatly increased growth of legumes, such as cow- 

 peas, peas, vetches, lucerne or clover, and thereby largely augments the 

 supply of organic matter, which may be the limiting factor in crop yields on 

 such soils. Indeed, the lack of nitrogen and organic matter in the soil may 

 easily render the application of phosphatic fertilisers unprofitable — a stata 

 of things often leading to their wrongful condemnation. 



