86 o 
Journal of Agricultural Research 
Vol. V, No. 18 
considered separately. The same is true of the nitrification results with 
ammonium sulphate and dried blood. 
Furthermore, the ammonification, nitrification, and azofication results 
are all in close agreement as to the relative effects on each of the various 
treatments; and, hence, the bacteriological results may be compared as 
a whole with the crop yields. 
An examination of the tables reveals the fact that a greater crop yield 
was secured where the 2-year rotation was followed than on the con¬ 
tinuous coin plot, and a still greater yield was secured where the 3-year 
rotation was followed. Exactly the same relations were found in the 
ammonification, nitrification, and azofication results. 
Where the clover was introduced into the 2-year rotation as a green 
manure a greater crop yield was obtained than where it was not used. 
Furthermore, a slightly greater yield was obtained than on the 3-year 
rotation plot. The bacteriological results are not in accord with these 
differences; but in most cases the variations were not large, and the 
differences in crop yield were not great. Hence, the lack of agreement 
here should not be considered of great significance. 
When cowpeas were used in the 2-year rotation, however, the yield 
was abnormally depressed. The bacterial activities were also depressed, 
but not to so great an extent. Evidently some unknown factor inter¬ 
fered here, as such a depression is hardly explainable. Where rye was 
turned under in the 2-year rotation the yield was less than on the regular 
2-year rotation plot, and corresponding depressions were noted in the 
bacterial activities. 
It is apparent that the ammonification, nitrification, and azofication 
results as a whole show a surprisingly close relation to the crop yield. 
Nitrification and ammonification tests frequently proceed in the same 
direction, and it is possible that after many confirmatory tests have been 
carried out it may be found that only one of these bacteriological tests 
of soils needs to be made. At the present time, however, the data 
available along this line are insufficient to warrant the interpretation of 
the results from one process as fitting another. 
It is hardly expected, however, that azofication results will run parallel 
with ammonification and nitrification tests in any large number of studies. 
Conditions which favor the latter processes need not necessarily favor 
azofication. 
These results as a whole, therefore, indicate that under normal soil 
conditions the ammonifying and nitrifying powers of soils may reflect 
fairly accurately their crop-producing power and show quite accurately 
the relative yields which will be secured. Only in special cases can 
similar dependence be placed on azofication results. These tentative 
conclusions have been further tested and are borne out by the later 
results. 
