198 AMMONIFICATION 



fluorescens, and many others are slow liquefiers. This indicate^ 

 that the class of organisms must play a very important role in the 

 degradation of the nitrogenous material of the soil. 



It is quite likely that the organisms are even more efficient in the 

 soil in the mixed cultures than they are in the pure cultures. For 

 the transforming of protein nitrogen to ammonia is a complex 

 process which must proceed by steps and some organisms must be 

 more efficient than are others in specific phases of the reaction. 

 But so far we have little definite information on this subject. 



Methods. Two methods are in general use for the determination 

 of the ammonifying powers of the soil. The one in which a definite 

 portion of soil is inoculated into a liquid media and after a given 

 time the ammonia determined; in the other the nitrogenous sub- 

 stance is incorporated into the soil and after a definite period the 

 ammonia determined. The latter method would appear to approach 

 more nearly field conditions, but both methods have their advocates. 

 It is not my purpose to go into the claims made for each, but suffice 

 it to state that Lohnis, who has made a careful study of each, finds 

 the more important factors in both to be: (1) Nature and quantity 

 of material used as substrata; (2) concentration and distribution of 

 the substrata in the medium; (3) aeration; (4) diffusion, absorption, 

 destruction or evaporation of metabolic products; (5) reaction of the 

 medium; (6) temperature; and (7) duration of the experiment. 



As was pointed out by Pagnoul in 1895, the formation of ammonia 

 in the soil is only a transition state of organic nitrogen in passing 

 to the nitrates. So that with either the solution or soil method, 

 what we measure is the accumulation of ammonia in the media and 

 not the actual quantity formed. Various factors may enter and slow 

 down the quantity of ammonia formed. This would be indicated 

 by a smaller quantity of ammonia in the soil, or the speed with which 

 the ammonia is transformed into nitrates may decrease, and hence the 

 ammonia accumulates while the actual quantity found is the same. 

 Moreover, it is well known that many microorganisms possess the 

 power of transforming ammonia into protein nitrogen, and this 

 factor may either increase or decrease with a corresponding change 

 in the ammonia of the soil. Where large quantities of ammonia are 

 being formed, part of it may be lost from the medium by volatiliza- 

 tion. The extent of this loss varies with the soil. Lemmermann 

 and Fresenius found the addition of calcium carbonate to a soil to 

 the extent of 1 per cent, reduced the volatilization of ammonium 

 carbonate and increased the absorptive power of the soil for ammonia. 

 Calcium sulphate and chlorid and magnesium chlorid have a similar 

 effect. Caustic lime has the opposite effect. The zeolites are very 

 effective in reducing the loss of ammonia from soil, and according to 

 Pfeiffer and coworkers the nitrogen so fixed is so firmly held that it 

 does not become available to plants during the first season. 



