234 STATE BOARD OF AGRICULTURE. 



NITROGEN. 



Nitrogen is the element usually least abundant in soils and is the ele- 

 ment most readily exhausted. It is also the most costly element to sup- 

 ply to the soil. Four-fifths of the volume of the atmosphere consists of 

 nitrogen, but to most plants this enormous supply is of no consequence 

 for they are entirely unable to assimilate it. A few plants belonging to 

 the clover class are enabled, because of the small nodules on their roots, 

 to change some of the atmospheric nitrogen into forms which can be 

 utilized by the growing plant. This fact partly explains why a soil im- 

 poverished, from a nitrogen standpoint, is so benefited by turning under 

 a heavy crop of clover as a green manure. Nitrogen is at the two extremes 

 of nature. It is nitrogen that is so sluggish and inactive that it has been 

 named "Azote, without life." Nitrogen does not support combustion, for 

 if a flame is put into a jar containing nitrogen alone, the flame is at once 

 extinguished. It is this same formerly inactiv^e nitrogen, however, the 

 various combinations of which form the deadliest explosives known. It is 

 the comjiouud of nitrogen that form some of the deadliest poisons known. 

 It is nitrogen that makes nitroglycerin and dynamite such power- 

 ful and destructive agents. It is nitrogen that makes prussic acid one of the 

 most deadly poisons known to man. It is this same nitrogen, another 

 of whose combinations, is such an all-essential element of animal food 

 Protein, or the albumen in eggs, the gluten in flour, the fibrin in meat, 

 and the casein in milk, is the most essential constituent of animal 

 food, and it is one of the various combinations of nitrogen. These con- 

 siderations may serve to show in part why nitrogen is so essential and 

 it is no wonder that its presence in the soil is of such vital interest to 

 vegetable life. Nitrogen is found in fertilizers as organic nitrogen and as 

 salts of ammonia and nitric acid. As organic nitogen it is present in the 

 scraps of meat, blood, vegetable matter, or leather; as a salt of ammonia 

 it is present, chiefly, as ammonium sulphate. As a salt of nitric acid, it 

 is present, chiefly, as nitrate of soda or Chili saltpeter. Nitrogen in the 

 form of ammonium salts and nitric acid salts is the most readily 

 available. Organic nitrogen must be disintegrated by agents in the soil 

 before it can be made available to the plant. There are, however, differ- 

 ences in the availability of organic nitrogen from different sources. 

 Nitrogen from blood, or seed meals, is much more readily available than 

 is the nitrogen in leather and tankage made from garbage materials. 



PHOSPHORIC ACID. 



Phosphorus in plants and fertilizers is usually expressed in the form 

 of phosphoric acid (P0O5). Phosphorus by itself is very inflammable and 

 is also a deadly poison. When united with oxygen to form phosphoric 

 acid it is not only harmless but essential to plant growth. It is usually 

 found in fertilizers in combination with lime or it may be as free phos- 

 phoric acid in super-phosphate fertilizers. Phosphoric acid is recognized 

 in fertilizers in three forms: 



1. Water-soluble phosphoric acid gives us phosphoric acid in the free 

 form as in true super-phosphates and as mono-calcic phosphate in which 

 forms it is readily soluble in water. 



2. Citrate soliible phosphoric acid gives us phosphoric acid in the form 



