Mar. 24, 1919 Ammonification of Manure in Soil 331 



inoculation of the soil and the amount of ammonia produced rather than 

 between the number of organisms present and the ammonia production. 

 The tests were continued until the apex of ammonia production was 

 apparently reached. After this point had been reached, a steady 

 decrease in ammonia production was noted, regardless of the number of 

 organisms present. This was undoubtedly due to the depletion of 

 available organic matter. 



DISCUSSION OF RESULTS 



The heterogeneous nature of soil, the great variety of organisms present, 

 and the varying moisture content are all factors which make it prac- 

 tically impossible to carry on a study of ammonification in the soil 

 under absolutely natural conditions. In order to control these things 

 and to obtain comparable data, it is necessary to bring the soil into 

 the laboratory for study. This introduces a difficulty, in that conditions 

 governing the activities of organisms in the laboratory are generally at 

 wide variance with conditions in the natural environment of these 

 organisms. The reason for this variance is twofold: First, laboratory 

 media may often be decidedly different from the soil in which the organ- 

 isms are native; and second, the organisms in pure culture, as they are 

 generally handled in the laboratory for purposes of control, do not 

 behave as they would in competition or in association with the other 

 organisms normally present in the soil. These artificial conditions must 

 be kept in mind in considering the results obtained in the present work, 

 but despite them there was one striking relation which invariably held 

 true: the spore forming B. cereus never multiplied in manured soil with 

 any degree of rapidity, while Ps. fluorescens and Ps. cavdatus always did. 



The data indicate that in soil where little organic matter is present and 

 the processes of soil decomposition are practically at a standstill the spore 

 former B. cereus occurs much more often than do the non-spore formers 

 Ps. fiuorescens and Ps. caudatus. When organic matter in the form of 

 manure has been added to that same soil, however, and the processes of 

 decomposition become active, the character of the flora changes entirely, 

 and Ps. fluorescens and Ps. caudatus predominate over B. cereus. But 

 the proof that these non-spore formers are the important ammonifiers in 

 manured soil is decidedly difficult to secure. 



As Conn (7, p. 254) has previously pointed out, there are four points 

 which must be established before we can show conclusively that any 

 particular chemical transformation in the soil is due to certain organisms: 



(i) The organism must be shown to be present in active form when the chemical 

 transformation under investigation is taking place; (2) it must be shown to occur in 

 larger numbers under such conditions than in the same soil in which the chemical 

 change is not occiuring; (3) it must be isolated from the soil and studied in piu-e cul- 

 ture; (4) the same chemical change must be produced by the organism in experi- 

 mentally inoculated soil, making the test, if possible, in unsterilized soil. The foxirth 



