Soil Changes Produced By Micro-organisms. 
2 9 
arable land or to more than a very small percentage. While the 
matter is eminently serious, it by no means justifies the position that 
our agricultural interests as a whole are in jeopardy.” 
A full account of this investigation has been published already 
(i), the results of which show that Azotobacter chroococcum is 
present in most of the soils examined and that the characteristic 
dark brown color referred to above is due, in a large part, to the 
pigment produced by Azotobacter chroococcum. 
In view of the results which we have obtained in our studies 
of non-symbiotic nitrogen fixation in Colorado soils, together with 
those cited in connection with ammonification and nitrification, we 
feel reasonably safe in asserting that the excessive nitrates which 
we find are the result of bacterial action. 
In order that the reader can have a more definite idea of the 
amount of nitrates which have been found in some of these once 
arable soils, I am giving below in Table No. 3, a few figures on this 
point which have been furnished to me by Dr. Headden. 
By way of comparison, I may say that an average amount of 
nitrate, expressed as nitrate of soda, for our cultivated fields is 
from .0037 to .0121 per cent., 150 to 450 pounds per acre-foot. 
Table No. 3. Nitrates in certain nitre soils. 
Percent 
Percent 
Material 
Percent 
nitrates in 
nitrates in 
Source 
examined 
water 
water 
air dried 
soluble 
soluble 
soil 
Black spot in 
Surface soil 
two 
barley field.. 
inches . 
134 
41-859 
5.628 
Young orchard 
Surface soil. 
Surface soil 
two 
22.466 
29.114 
6.54 
Young orchard 
inches . 
8.23 
8 -!73 
•673 
Alfalfa field., 
Top soil five inches 
7.78 
33 -o 6 
2-571 
Surface soil 
two 
Oat field. 
inches . 
54 2 
50.221 
2.722 
Orchard . 
Top soil 12 inches 
6.51 
43-57 
2.837 
Corn and rye... 
Surface soil 
4.67 
7 - 35 2 
• 34 2 
Old orchaird. 
Surface soil .. 
6.65 
5-746 
.382 
These figur 
•es may mean 
V 
more when I 
say that 
one of the 
above samples, which carried 2.873 P er cent, of nitrates in the 
( 1 ) Bacteriological Studies of the Fixation of Nitrogen in Certain ColoradcrSoils, Bulletin 
179. Colorado Experiment Station, 1911. 
