jan. 31,1916 Bacterial Activity in Soils and Crop Production 
863 
If these results are examined, it is found that practically uniform 
agreement was secured with the various methods—i. e., the relative 
ammonifying powers of the soils were the same whether the dried-blood 
or the casein method was employed, and it made little difference whether 
the dried-blood-air-dry-soil method was employed or the dried-blood- 
fresh-soil method was used. Similarly, in the case of nitrification, the 
same relative results were obtained whether the air-dry-soil method or 
the fresh-soil method was employed. It is unnecessary, therefore, to 
consider the results individually, and comparisons will merely be made 
between the bacterial results and the crop yields. 
The largest crop yield was obtained in this year on the plot under the 
2-year rotation with clover turned under. Similarly, the greatest 
ammonifying power and the greatest nitrifying power were found in this 
soil. The soil under the 3-year rotation (corn, oats, and clover) was 
second in crop yield and in bacterial activities; the 2-year rotation with 
cowpeas as a green manure induced a slightly smaller crop yield and 
lower bacterial action; the 4-year rotation was still lower; the 2-year 
rotation (com and oats) lower yet; the 2-year rotation with rye turned 
under gave a still smaller crop yield and lower bacterial action; and the 
continuous-crop plot was at the bottom of the list. 
It is evident from these results that the ammonification and nitrifi¬ 
cation of nitrogenous organic material in soils and their crop-producing 
power are very closely related and that tests of the power of soils to 
produce ammonia or nitrates may be an indication of their crop-producing 
power, or at least of their relative crop-producing ability. Previous 
results are also confirmed regarding the similarity of the effects of soil 
treatment or ammonification and nitrification. Such need not always be 
the case, of course, as it is possible to conceive of conditions affecting 
the nitrifying organisms which do not similarly affect the ammonifiers, 
but it seems to be the case that in ordinary field conditions the two proc¬ 
esses are quite similarly affected by treatment and probably only one 
process need be tested to gain some idea of the relative crop-producing 
power of soils. 
TESTS ON ROTATION PLOTS IN 1913 
The experiment on the same series of plots was continued in 1913, 
different individual plots being used for com. 
Three samplings were made during the season—on August 15, August 
23, and August 26. Ammonification tests only were carried on, owing to 
the pressure of other work; and only one method, the casein-fresh-soil 
method, was employed. The crop yields were obtained as previously. 
Again, the moisture content of the soils at the different samplings varied 
so slightly that the differences may be considered negligible from the 
standpoint of the effects of treatment. 
The results of the ammonification tests appear in Table XIII, and the 
crop yields are given in Table XIV. 
