ORCHARD MANAGEMENT 131 



There are three stages in the process. In the first stage 

 one set of bacteria causes the nitrogen and hydrogen in the 

 decaying vegetable matter to unite, forming a compound 

 called ammonia. Sometimes the odor of ammonia can be 

 detected as it escapes into the air from decaying piles of 

 moist leaves or manure. The ammonia that is escaping car- 

 ries large quantities of nitrogen with it, for ammonia is by 

 weight fourteen-seventeenths nitrogen. At the present price 

 of this element, it is easy to see that escaping ammonia 

 represents a very large financial loss. 



After the ammonia is produced, other bacteria act on it, 

 changing it to nitrous acid. Then the nitrous acid is acted 

 on by still another set of bacteria, which change it into nitric 

 acid. Nitric acid as it comes in contact with the soil unites 

 with various compounds already there, forming soluble salts 

 known as nitrates which are available for plant use. All the 

 nitrogen which is "locked up" in organic matter must first 

 go through this process before it can be used by the plant. 

 Therefore, organic fertilizers which carry nitrogen, such as 

 blood and tankage, are not immediately available to the 

 plant, but must stay in the soil long enough for the nitrifica- 

 tion process to take place. The nitrogen is then available. 



219. Phosphorus is a yellowish semi-transparent sub- 

 stance. Because of its affinity for oxygen, it must be kept 

 under water or oil; if exposed to the air for even a brief time, 

 it forms a white smoke-like substance, a compound composed 

 of oxygen and phosphorus (phosphorus pentoxide) which is 

 heavier than air, and which dissolves in water, forming 

 phosphoric acid. If introduced into the soil, it there unites 

 with various soil substances, forming phosphates. Phos- 

 phates are among the most important plant-foods in the soil. 

 The phosphorus used in fertilizers is derived principally from 

 calcium phosphate and from ground bone. The former is a 

 mineral occurring especially in Tennessee and South Carolina. 

 It is mined, ground fine, and sold in this form as raw rock 



