78 



T. Lyttleton Lyon and James A. Bizzell 



tion was probably curtailed by the inhibiting action of the products of the 

 nitrifying bacteria. 



The natural inference from these results is that in some way the growth 

 of alfalfa renders this soil capable of developing nitrates more rapidly than 

 does the growth of timothy, and that this quality persists in the soil for at 

 least one or two years after the crops are removed. 



In addition to the incubation tests of the natural soil, further experi- 

 ments were conducted by adding to 100 grams of fresh soil 100 milligrams 

 of dried blood and incubating as before. In Table 28 appears a statement 

 of the quantity of nitrates produced in fourteen days under these condi- 

 tions, and also the excess of nitrates when the soil is incubated with dried 

 blood over those formed by incubation of the natural soil: 



TABLE 28. 



Nitrates Produced by Incubation with Dried Blood 

 (Parts per Million) 



Plat 



Crop 



Nitrates produced 

 in fourteen days 



Excess of nitrates with 

 dried blood over 

 those with direct 

 incubation 





May 10 



May 29 



May 10 



May 29 



4001 A, 4001 C 



Alfalfa 



None 



Timothy 



None 



172 

 196 

 133 

 130 



177 

 150 

 108 

 105 



124 



148 



83 



88 



118 



4001 A, 4001 C 



4002 A, 4002 C 



4002 A, 4002 C 



110 

 67 



72 



Here again there is shown to be a more active nitrate production in the 

 alfalfa soil than in the timothy soil. The object in incorporating dried 

 blood with the soil was to insure the presence of a large quantity of easily 

 ammonifiable and nitrifiable nitrogen, thus making it possible to measure 

 the activity of the ammonifjdng and nitrifying organisms independently of 

 the native nitrogenous matter which might be present in larger quantity 

 in the alfalfa than in the timothy soil. The activity of the nitrate-pro- 

 ducing bacteria may therefore best be represented by the values obtained 

 by subtracting the nitrates produced by direct incubation from those 

 obtained by incubation with dried blood. The two last columns of Table 



