Soil Changes Produced By Micro-organisms. 19 
those isolated from American and Australian samples. To the 
organism accomplishing tlie second step, known as me nunc or 
innate bacteria, lie gave the name iMitrubacter. 
In addition to tnese forms, ivaserer claims to have isolated an 
organism, tiucillus mtratur, which is capable ot oxidizing ammonia 
directly to nitrate. Corroborative evidence upon tins discovery 
has not been received as yet, and should it be continued, even then, 
the number of known mtntying organisms is very small. 
Nitrification, then, may be dehned as the process by which 
ammonia compounds are changed to nitrites and 111 nates by the 
action ot mtriiying bacteria. 
Inasmuch as nitrates in reasonable amounts are very desirable 
assets to all soils, it may be worth while to ascertain under wnat 
conditions nitrification proceeds most rapidly, in the first place, 
it is obvious that the soil must be supplied with adequate organic 
matter troiii which the ammonifying bacteria can produce ammonia. 
Snice nitrification is an oxidizing process, the soil must be well 
aerated by thorough cultivation and proper drainage. One of the 
reasons that surtace soil is more fertile than sub-soil is because 
the looser texture of the upper layers permits the easy penetration 
of atmospheric oxygen, a requirement for active nitrification. Conn 
states that, “about (35 per cent, of the total nitrification occurs in 
the upper twelve inches of soil, 30 per cent, more in the layers from 
twelve to thirty inches lower, and little or none below this." 
Sufficient moisture must be furnished for the growth of the bac¬ 
teria, about the same as for ordinary crops. Nitrification takes 
place through a wide range of temperatures; feeble at 40° F.; 
marked at 55 0 F.; and best at 85° F. From this it will be ob¬ 
served that nitrification in the soil is going 011 most vigorously 
from July to October, a time of the year when the nitrates formed 
are of immense value to growing crops. The toxic substances 
excreted by the roots of higher plants are believed to be injurious 
to the nitrifying organisms, and therefore the urgent need of crop 
rotations. Acid soils prohibit nitrification, and if such conditions 
exist, they should be corrected by liming. There should be an 
ample supply of lime, magnesia and other basic materials to insure 
the prompt neutralization of the nitrous and nitric acid as well as 
any organic acids that may be formed. Excessive amounts of 
certain alkali salts may prove objectionable. 
Among the numerous theories which have been advanced to 
account for the saltpeter beds of Chile and Peru, is the belief that 
the areas now occupied by these deposits were at one time arms of 
