46 The Colorado Experiment Station 
our normal soils in ammonifying efficiency.’' “Compared with soils 
from other localities, our nitre soils excel in ammonifying efficiency.” 
It has been stated and emphasized that our soil conditions seem 
exceedingly favorable to the development of bacteria, especially such as 
require an alkaline medium for their development. 
It is stated in Bulletin 178, p. 90, that quite a vigorous development 
of algae and diatoms took place on the soil that I used in my incubation 
experiments when it was exposed to the light in a culture dish. I have 
since that tested other samples of soil and found that they all yielded an 
abundant growth of algae. Mr. W. W. Robbins has taken up the subject 
systematically and has published some of his observations in Bulletin 184. 
Out of twenty-two samples of soil taken for experiment, only two failed 
to give a growth of algae, and one of these was a sample of raw, unculti¬ 
vated, adobe soil. This abundant presence of algae has been mentioned 
as a possible source of energy. 
SUMMARY AND CONCLUSIONS. 
Our soils, as is shown by numerous analyses, are not unusually rich 
in nitrogen. They are only moderately well supplied with it and the 
unusual amounts of nitrates found cannot be produced by the nitrification 
of the supply already in the soil, but this supply must be supplemented by 
nitrogen from some other source, we believe that this other source is the 
atmosphere. 
The nitric-nitrogen does not owe its origin to the same sources that 
furnish our ordinary white alkalis which, beyond question are decompo¬ 
sition products of our common minerals, but principally of the feldspars, 
by agencies now at work. 
The distribution of the nitrates in our soils cannot be consistently 
accounted for by any theory of concentration of pre-existing nitrates. 
Their distribution is wholly independent of that of the alkalis—the latter 
being practically free from nitrates, as much so as a great many of our 
soils, while the aqueous extract of our soils, especially those showing the 
brown color due to Azotobacter, are extremely rich in calcic and magnesic 
nitrates. 
The ratio of the nitric to the total nitrogen in many of our soils, 
particularly in the surface portion of the brown spots, is very high due 
to fixation and nitrifcation. 
The deeper portions of the soil under these brown spots are usually 
poor in nitrates, but irrigation or rainfall may carry the nitrates on the 
surface downward, even into the ground water. While the solutions of 
potassic and sodic nitrates show capillary action, it is doubtful whether 
the calcic and magnesic nitrates do not move downward, especially in 
soils that are quite moist, rather than upward. The calcic and magnesic 
nitrates do not show capillary movement exposed in glass vessels, as do 
sodic chlorid and nitrate, ammonic chlorid and many other salts. 
The solubility of the nitrates contributes to their easy and rapid 
removal by downward moving waters. The soil seems to have but little 
or no power to retain these salts, nitrates, so they pass readily into the 
