RELATION BETWEEN CERTAIN BACTERIAL ACTIVITIES 
IN SOILS AND THEIR CROP-PRODUCING POWER 
By Percy Edgar Brown, 
Chief in Soil Chemistry and Bacteriology , Iowa Agricultural Experiment Station 
INTRODUCTION 
Soil-bacteriological investigations in the past have dealt almost ex¬ 
clusively with the occurrence and activities of micro-organisms in the 
soil, and no attempt has been made, from the standpoint of crop pro¬ 
duction, to interpret the results obtained. 
A knowledge of the relation of soil bacteria to soil fertility is of con¬ 
siderable importance, however, if the subject is to be of any value in 
practical agriculture. While, therefore, much work on methods remaips 
to be done, so much knowledge concerning bacterial action in soils has 
been accumulated during the last few years that it seems time now to 
call attention to the practical phase of the subject, to attempt at least 
to correlate the results secured with known facts regarding soil fertility. 
The purpose of these experiments has been to study certain bacterial 
activities in field soils in the attempt to secure information regarding 
their relation to the actual crops produced. If special methods of soil 
treatment exert similar effects on certain bacterial activities and on crops, 
it may be assumed that there is a fairly definite relation between the 
two, and the particular bacterial activities in a soil may indicate its 
crop-producing power. Thus, if in laboratory tests the ammonifying 
power, the nitrifying power, or the azofying power of a soil is enhanced 
by some method of soil treatment and the crop production is also in¬ 
creased, the conclusion that ammonification, nitrification, or azofication 
and crop production are very closely related would be well warranted. 
Tests of such bacterial action in soils would therefore constitute a means 
of ascertaining their crop-producing power, and the importance of obtain¬ 
ing advance information along this line is evident. 
Experiments covering many years of varying seasons and including 
tests of all varieties of treatments must, of course, be carried out before 
any definite conclusions can be reached. The experiments reported 
here were secured on three series of plots under definite systems of 
treatment, and it was intended in undertaking the work to carry it on 
for a long period of years before attempting to draw conclusions. Inas¬ 
much, however, as the particular plots were of necessity relinquished, 
owing to the development of certain departments of the State College, 
and studies of a like nature can not be undertaken on new plots until 
several years of special treatment have elapsed, it has been deemed 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. # 
bv 
( 855 ) 
Vol. V, No. iS 
Jan. 31, 1916 
Iowa—1 
