8 
Colorado Experiment Station. 
concentration of the salts from the irrigation and ground waters in 
the surface layers of the soil. This, of course, presupposes the exist¬ 
ence of a nitrate bearing stratum from which to derive this salt. In 
the first place, no such stratum or bed is known to exist within the 
state or neighboring states, and, in the second place, our deep well 
waters, ground waters and surface waters contain an insignificant and 
negligible quantity of nitrate. 
That these spots are the remains of great herds of extinct animals 
which perished from some unknown cause is highly improbable, first, 
because the areas involved are too great; second, as mentioned before, 
the present spots are increasing in size, and, third, spots are appearing 
today in localities where the trouble has never been reported before. 
For the same reasons, there is no ground for believing that these 
areas are nitre beds related to some established geological horizon. 
Unable to account for this phenomenon .satisfactorily in any of the 
foregoing ways, we have been forced to the one remaining possibility, 
namely, the formation of the nitrates in situ. 
Having reached this conclusion only after a thorough study of 
all other possible causes, Dr. Headden presented the question to me as 
a purely bacteriological problem, amenable to bacteriological methods. 
Under ordinary circumstances, I should have looked to the 
ammonifying and nitrifying flora of our soils as the responsible 
agents, but the amount of organic matter in our soils, both cultivated 
and virgin, is far too small to supply the organic nitrogen required for 
the manufacture of such quantities of nitrate. Confronted by this 
nitrate monstrosity on the one hand, and by the dearth of nitrogen on 
the other, I must confess that the question was somewhat perplexing. 
However, it seemed to me that the logical method of procedure was 
to look elsewhere than to the soil for a source of nitrogen. Quite 
naturally, I turned my attention to the atmosphere. If it could be 
demonstrated that our soils had the power of fixing atmospheric nitro¬ 
gen through the agency of Azotobacter and did fix it, I felt reasonably 
certain that it was only a question of time until we could show that the 
ammonifying and nitrifying organisms were utilizing this new supply 
of nitrogen to build up nitrates. 
With this as a starting point, I have begun my studies on the 
fixation of nitrogen by Azotobacter in certain Colorado soils. 
Scope of Present WoRk. 
Our studies on the fixation of atmospheric nitrogen, presented 
herein, have not been confined to fixation in solutions alone, but have 
been extended to include fixation in the soil itself. Two such soil ex¬ 
periments are reported here, but the greater part of this data has been 
reserved for another bulletin. 
Extended studies on the ammonifying and nitrifying efficiency of 
these same soils are in progress at the present time, the results of which 
will constitute the text for a future publication. 
