Jan. 31, 1916 Bacterial Activity in Soils and Crop Production 
869 
The ammonification results by the two methods employed were very 
similar, as also were the nitrification results; hence, these results need 
not be considered separately. 
If the bacterial tests are compared with the crop yields, it is found that 
the lime increased ammonification, nitrification, and azofication in the 
soils, and the crop yield was similarly increased, the larger amount of 
lime bringing about the greater effect on the bacteria but exerting no 
further increasing effect on the crop grown. 
These results as a whole therefore check those obtained on the plots 
under other methods of treament and show that bacterial transforma¬ 
tions of nitrogenous compounds in the soil or, rather, the ability of soils 
to bring about the simplification of nitrogenous materials or the addition 
of nitrogen, may be considerably modified by various methods of soil 
treatment. Furthermore, they check previous results in showing that 
certain bacterial activities in the soil may be very closely related to the 
actual crop-producing power of the soil. The ammonifying power of 
soils, their nitrifying power, or even, in certain cases, their azofying 
power may therefore indicate the crop-producing power of soils or, at 
least, their relative crop-producing power. 
CONCLUSIONS 
(1) These experiments as a whole represent a line of investigation in 
soil bacteriology which it is believed will ultimately place the subject on 
a more practical basis—a basis which will permit the direct application 
of the results obtained to the solution of soil-fertility problems. 
(2) The relations between the bacterial activities studied and the actual 
crop yields on these plots have proved so striking and so consistent that 
it was felt that accidental coincidence had been practically eliminated 
and the results might be considered to give a strong indication that 
certain bacterial activities in field soils are very closely associated with 
crop yields. 
(3) Furthermore, the tentative conclusion presents itself that tests of 
such bacterial activities in the laboratory may indicate quite accurately 
the crop-producing power of a soil or, at least, the relative crop-producing 
power of several soils. 
(4) If, further, more exhaustive tests confirm -these preliminary obser¬ 
vations, it may be possible to secure advance information regarding 
the crop-producing power of soils by means of laboratory tests of bac¬ 
terial action in those soils. 
