264 PLANT BIOCHEMISTRY 



fertilizer the composition of which is given as 6-0-12 contains 6 ])cr 

 cent nitrogen, 9 per cent phosphorus calculated as PoOr,, and 12 per 

 cent potassiinn calculated as K^O. 



Becatise of the above conventions for indicating the analysis, it is 

 customary to speak of fertilizer materials and mixtures as containing 

 nitrogen, phosphoric acid, and potash. Until recent years it was also 

 customary to speak of the ammonia instead of the nitrogen content 

 of fertilizers. These terms have no significance with respect to the 

 compounds in which the elements are found in fertilizers. Each of 

 the three elements may be present in several different compounds. 



Nitrogen Fertilizers 



Foin- types of nitrogenous fertilizers are available. Hicsc arc ni- 

 trates, ammoniimi compounds, organic compounds of nitrogen, and 

 animal and vegetable residues. 



Nitrates. The most common nitrate available for fertilizer is sodium 

 nitrate (nitrate of soda). It occurs in a mixture of various salts, called 

 caliche, found in large deposits in northern Chile. After purification 

 by selective crystallization, the nitrate of soda is melted and sprayed 

 into an enclosed chamber. The drops, on cooling, solidify into small 

 shot-like pellets, a form that is convenient for packaging and handling. 

 This pellet form contains about 99 per cent sodium nitrate. 



Potassium nitrate is a desirable source of both nitrogen and potas- 

 sium. However, the supply of nitrate of potash is quite limited. The 

 principal source is caliche, which contains 2 to ?> per cent potassium 

 nitrate. The commercial product derived from caliche is a crude 

 grade which contains both sodium and potassium nitrate and has a 

 nitrogen content of about 14 per cent and a potash content (KoO) of 

 about 15 per cent. Small amounts of purer KNO3 are also available 

 for fertilizer use. 



Calcium nitrate, also known as nitrate of lime and Norwegian salt- 

 peter, is an excellent source of quickly available nitrogen, containing 

 about 16 per cent nitrogen and 34 per cent calcium, expressed as CaO. 

 It is much more hygroscopic than cither of the above nitrates, and 

 because of this it is more difficult to apply to the soil. Owing to this 

 fault it is not entirely satisfactory as a fertilizer, and its use has been 

 limited. It is made in Norway and Germany by the neutralization of 

 nitric acid with calcium carbonate. 



Ammonium nitrate is also used as a nitrogenous fertilizer to some 

 extent. Ammonium nitrate is a hazardous material, for it will ignite 

 and detonate under certain conditions. 



Nitrates are easily soluble in water, and this characteristic ensures 



