218 NITRIFICATION 



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 pre- 

 sented results with soils where nitrification is almost as active in 

 the subsoil as in the surface soil when the subsoil is aerated. In 

 1912 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 author found soil 

 from second and third foot-sections to nitrify dried blood quite 

 readily, as is shown below: 



Irrigated Dry-farm 



Depth Soil Soil 



First twelve inches 19.39 5.25 



Second twelve inches ........ 2.70 2.41 



Third twelve inches 1.98 1 . 55 



These are the averages of several hundred examinations, and 

 many soils which were fairly heavy clays showed active nitrifica- 

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

 observed 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. 



Reaction of Media. Boussingault long ago observed that many 

 forest soils do not contain nitrates, and later this was verified by 

 Breal and others. We now know that the absence of nitrates is 

 due to the acid reaction of a soil which contains an excess of organic 

 matter. The nitric ferment does not act in an acid medium; hence, 

 we have the explanation of the great benefit derived from the use 

 of basic substance. 



Experiments by Wiley and Elwell in which solutions containing 

 calcium chlorid and water were seeded with nitrifying ferments 

 continued to nitrify until the medium contained an acidity equiva- 

 lent to 4 c.c. of normal acid per 100. 



Dumont and Crochetelle's experiments are of the same order. 

 They took soil which had been in grass from time immemorial and 

 which contained 6.84 per cent, of humus. This was treated with 

 variable quantities of potassium carbonate. It was stirred and 

 watered several times during the experiment and after one month 

 the nitrates were extracted with the following results: nitric nitro- 

 gen, per 1000 grams, of soil without addition of potassium car- 

 bonate, 70 mgs.; with 1 gram of potassium carbonate, 160 rags.; 

 with 2 grams of potassium carbonate, 230 mgs. ; with 3 grams, 250 

 mgs.; with 4 grams, 130 mgs.; with 5 grams, 73 mgs. In similar 



