COMMERCIAL FERTILIZERS 57 



brought about through decomposition. The nitrogen thus resulting is, 

 therefore, distributed through a considerable period of time. It is often 

 used as a part of the nitrogen supply for crops with a long growing season. 



Dried blood is also an organic source of nitrogen, containing on an 

 average 10 per cent of this element. It is easily decomposed and some- 

 what more available than nitrogen in cottonseed meal. 



Tankage contains nitrogen in variable quantities, ranging from 5 to 

 12 per cent. It may also contain from 7 to 20 per cent of phosphoric 

 acid. The nitrogen in tankage is slowly available. 



Forms of nitrogen that have more recently found their way into the 

 market are cyanamide and lime nitrate. These are manufactured prod- 

 ucts in which the nitrogen is secured directly from the air through certain 

 chemical and electrical processes. The nitrogen in these forms is not 

 so available as that in nitrate of soda or sulphate of ammonia, although 

 it is considered more readily available than most of the organic forms. 



Phosphorus. This constituent is available in the form of acid 

 phosphate, which contains 14 to 16 per cent of phosphoric acid or 6 to 7 

 per cent of phosphorus. Mcst of the phosphorus is in an available form. 

 Acid phosphate is made by treating a given bulk of finely pulverized 

 phosphate rock with an equal weight of crude commercial sulphuric acid. 

 The reaction that takes place makes the phosphorus available. It is 

 this material that is chiefly used in the manufacture of complete com- 

 mercial fertilizers. Phosphoric acid costs from four to five cents per 

 pound in acid phosphate, depending on location and size of purchases. 

 (As this goes to press, prices have advanced 25 to 30 per cent. This 

 advance is probably temporary.) 



There is now an increased tendency to make direct use of the raw 

 rock phosphate in a finely pulverized form. Such rock contains the 

 equivalent of 28 to 35 per cent of phosphoric acid, but it is in an insoluble 

 form and can be economically used only on soils that are well supplied 

 with organic matter or in conjunction with barnyard or stable manure 

 and green manure crops. The general use of raw rock phosphate has not 

 been advisable on the soils of the eastern and southern part of the United 

 States. On the other hand, the raw rock phosphate has given good results 

 on the prairie soils of Indiana, Illinois, Iowa and some other states. 

 The cost of phosphoric acid in this form is equivalent to two cents per 

 pound or a little less. 



Basic slag, sometimes known as Thomas Phosphate, is a by-product 

 of steel mills which is finely ground and used as a source of phosphorus. 

 It is similar to raw rock phosphate, slightly more available and contains 

 the equivalent of 15 to 18 per cent of phosphoric acid. 



There are two types of bone meal on the market, raw bone and 

 steamed bone. The raw bone is fresh bone which has been finely ground. 

 Raw bone contains about 20 per cent of phosphoric acid and 4 per cent 

 of nitrogen. Bone which has the fat and gelatin removed by extracting 



