CUKMICAL KLKMKNTS NEEDKO llV PLANTS .^ 



gaseous state. In combination this element is found in many 

 substances such as ammonia, sodium nitrate (Chile saltpeter), 

 potassium nitrate and many organic compounds. Certain plants, 

 namely the legumes, of which the pea, bean, alfalfa, clovers, 

 covvpea, soy bean, etc., are members, have the power of gather- 

 ing nitrogen from the air, by means of certain growths (tuber- 

 cles ) on their roots. "^ Although nitrogen is abundant in the free 

 state it cannot be used as such by most plants and it must be 

 combined with other elements to be available as ])lant food. 

 Nitrogen as sold in fertilizers is in combination with other ele- 

 ments, and is the most fugitive and expensive of the essential 

 elements. This will be described more fully later on. 



Carbon. — This element is found in the free state in charcoal, 

 graphite and diamonds. In coal it is also present in an impure 

 state. Muck and peat contain considerable carbon. Humus 

 (the decayed organic matter in soils) is made up partly of car- 

 bon. In combination with oxygen we find carbon as carbon 

 dioxide (carbonic acid gas) in the air. It is present in greater 

 quantities in plant life than any other element. Henry^ says: 

 "10,000 volumes of air contain about 3 volumes of carlx)nic acid 

 gas ; 32 cubic yards of air hold one pound of this gas. An acre 

 of growing wheat will gather during four months, 2,000 pounds 

 of carbonic acid gas, or an amount equal to all the air contains 

 over the same area of land to a height of three miles." All 

 of our farm crops use a great amount of carbon in the form of 

 carbonic acid gas. All carbonates (limestone, chalk, marble, 

 shells, etc.) and all organic substances contain carbon. The car- 

 bonates of lime found in the soil exert a great influence upon the 

 conversion of some forms of nitrogen into available plant food 

 and in the general physical condition of the soil. 



Potassium in combination is very common. It is mined in large 

 quantities as potas.sium salts in the Stassfurt mines of Germany. 

 The presence of this element in wood ashes, as potassium car- 

 bonate, makes this substance a valuable fertilizer. Potassium 

 is found in most rocks and soils. In plants it is associated with 

 organic acids. It is found in sea water and saltpeter. This 



1 Feeds and Feeding. 



