228 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



(2) The second method 1 consists in inoculating the soil or seed 

 with a pure culture of the necessary organisms. This method 

 was patented in Germany in 1880, but did not prove a commercial 

 success. The method has been modified, and cultures are 

 now upon the market. Pure cultures of the symbiotic 

 bacteria may easily be prepared by inoculating a suitable 

 sterilized culture medium with the bacteria. The bacteria 

 are sent in a sealed tube ; before inoculating the seed or soil their 

 number is increased by allowing them to multiply in a large quan- 

 tity of water provided with necessary salts and sugar. The seed 

 are then soaked in this liquid, dried, and planted, or the liquid is 

 mixed with soil and the soil distributed and plowed under. 



The necessary bacteria are so generally distributed that it is 

 often unnecessary to inoculate the soil. They grow not only upon 

 cultivated plants, but also on many varieties of wild plants. 



Changes of Organic Matter. The organic matter in the soil 

 consists of the unchanged residues of plants and animals, and the 

 products formed from them by bacteria and other forms of life. 

 Decay takes place in two directions, according to the presence of 

 an abundance or a deficiency of air. 



In the presence of an abundance of air, decay is oxidation; the 

 final products are water, carbon dioxide, ammonia, and nitrates, 

 while the mineral material is left in forms which can be assimi- 

 lated by plants. 



In the presence of little or no air, decay is a reducing process, 

 oxygen is taken away from nitrates, or the higher oxides of man- 

 ganese or rron. Gaseous products, such as carbon dioxide, marsh 

 gas, hydrogen, and free nitrogen, are produced in comparatively 

 srmll quantities and slowly. The organic material is converted 

 into highly resistant bodies which hold their mineral content in 

 forms not assimilable by plants. The vegetable matter is con- 

 verted into brown substances, partly soluble in water and impart- 

 ing a brown color to it. The compounds produced are acid sub- 

 stances, somewhat antiseptic in nature and retard the decay of the 

 vegetable matter. The oxygen required for the production of 

 1 Progress in Legume Inoculation, Farmers' Bulletin 315, U. S. D. A. 



