F pilnts sources ' but chiefly from decaying vegetable matter and 



the weathering of the mineral matter of the soil. Both 



3* these processes supply Potash and 



Natural Plant P nos P nor i c Acid, but only the former 



Food. supplies Nitrate. Whether the soil has 



been fertilized or not, there are certain 



signs which indicate the need of plant food more or 



less early in the growth of the crop. If a crop appears 



to make a slow growth, or seems sickly in color, it does 



not greatly matter whether the soil is deficient in 



Nitrate or simply that the Nitrogen present has not 



been Nitrated and so is not available; the remedy lies 



in top-dressings of the immediately available form of 



Nitrate of Soda. 



FERTILIZERS EMPLOYED AS A SOURCE 

 OF NITROGEN. 



Nitrate of Soda. This is probably the best known 

 and most popular source of nitrogen amongst farmers. 



Its origin is the extensive deposits of crude Nitrate 

 of Soda discovered in the rainless districts on the west 

 coast of South America. 



Since all nitrogenous compounds must first be con- 

 verted into nitrates before being assimilated by plants, 

 Nitrate of Soda contains its nitrogen in an easily assim- 

 ilable form, and is, therefore, quick in action. 



Owing to this fact, it almost invariably gives best 

 results when applied in two or more applications, the 

 first being given at the commencement of growth, and 

 the succeeding ones at intervals of from two to three 

 weeks. 



Sulphate of Ammonia. The origin or source of 

 this material is coal, which contains 1^ to 2 per cent, 

 of nitrogen. It is chiefly a by-product of gas works. 

 It is slower in its action than Nitrate of Soda, since, in 

 order to render the ammonia available to plants, it 

 must first be converted into a nitrate, which process is 

 performed by certain soil bacteria. 



