INFLUENCE OF CROP, SEASON, AND WATER ON THE 
BACTERIAL ACTIVITIES OF THE SOIL 
By J. E. Greaves, Robert Stewart, and C. T. Hirst, of the Departments of Bacteri¬ 
ology and Chemistry , Utah Agricultural Experiment Station 
INTRODUCTION 
It is of the utmost importance that the quality and quantity of plant 
food rendered available during the season nicely balance that required 
by the growing plant, for then we have maximum yield with minimum 
loss of soil fertility. Most of the changes which take place in the soil 
constituents are wrought by microorganisms, which bring about the 
transformation through which nitrogen passes in the soil—that is to 
say, the transformation from its inert form in the atmosphere to a form 
available to the growing plant. Furthermore, they play an essential 
part in the cycles through which hydrogen, sulphur, and carbon pass. 
Bacteria bring about the mineralization of calcium, iron, phosphorus, 
and many other inorganic constituents of the plant and animal residues 
in the soil. Moreover, many of these substances are changed from the 
insoluble to the soluble form and thus are made available to the growing 
plant by bacterial activity. At times bacteria have an opposite effect 
and render many of these substances insoluble, thus preventing in a degree 
their loss to the growing plant. Or at times they may even compete 
with the higher plant for the limited supply of nutrient in the soil. 
The speed with which these transformations take place within a soil 
is governed, amongst other factors, by the season of the year, the crop 
growing upon the soil, and the water which that soil receives. These 
investigations were undertaken, therefore, with the hope of throwing 
definite light upon the magnitude of these influences and, furthermore, 
to correlate the results obtained by the various methods, one with the 
other, and these in turn with the crop-producing powers of the soil. 
For these reasons in this work a direct determination was made of 
the nitric-nitrogen content of the soil as soon as it was taken from the 
field while other portions of the same samples were used for the deter¬ 
mination of the ammonifying and nitrifying powers of the soil. Counts 
were also made of the number of bacteria developing from the soil on 
synthetic agar. 
A careful review of literature dealing with this phase of the subject 
has been made, and there is given below a r£sum£ of the most important. 
Journal of Agricultural Research, 
Washington, D. C. 
id 
(293) 
Vol. IX, No. 9 
May 28,1917 
Key No. Utah—6 
