NITRIFICATION 123 



their natural habitat. Thomasen found the nitrite organism in 

 samples of ooze from the bottom of the Kiel Fiord, but not in 

 the sea water nor on the Plankton or the iixed algae. It was also 

 found in similar samples of soil from the vicinity of Helgoland 

 and in slime from the bottom of the Bay of Naples, but only in 

 samples taken near the land. They are not found nor do they 

 function in sea water. 



Warington failed to find the nitrifying ferments in a clay 

 soil below eighteen inches, and this is in keeping with the findings 

 of Ladd at North Dakota. For a long time it was considered 

 that they are found only in the surface soil, but in 1906 Welbel 

 presented results with soils where nitrification is almost as 

 active in the subsoil as in the surface soil when the subsoil is 

 aerated. In 19 12 C. B. Lipman found them often to a depth 

 of five or six feet in soils of the arid regions. In one case soil 

 from the eight foot depth showed a vigorous nitrifying power. 

 The Senior author found soil from second and third foot-sec- 

 tions to nitrify dried blood quite readily, as is shown on page 



124. 



These are the averages of several hundred examinations, and 

 many soils were fairly heavy clays and showed active nitrification 

 in the second and third foot-sections. This great difference ob- 

 served in the arid regions is due mainly to a better aeration of 

 these subsoils which, because of the peculiar climatic conditions, 

 the arid soils are not as rich in clay as are the subsoils of the 

 humid regions. Moreover, the plants in the arid regions root to 

 a great depth in search of water. These decaying roots loosen up 

 the subsoil and also furnish food for bacterial growth. 



Factors Governing Nitrification. — ^The soil is the laboratory 

 in which the tiny nitrifiers work. As a laboratory it must contain 

 the material on which they are to work and also means by which 

 the finished product, nitric acid, can be removed so it will not 

 impede their activity. These organisms cannot produce something 

 from nothing, nor can they increase one iota the total fertility in 

 the soil. They can change only its form. 



Manure—The nitrifiers act upon ammonia and produce from 



