The Fixation oe Nitrogen in Colorado Soils 47 
drainage waters of the country, but our ground and drainage waters are 
rich in nitrates only when they come from nitre areas. Of the many 
ordinary and artesian well waters that I have examined, I have found but 
two that contain unusual quantities of nitrates. I have described these in 
Bulletin 178. 
The shales and sandstone do not furnish these nitrates or else all of 
our well waters would be rich in nitrates, but they are not richer in 
nitrates than well waters usually are. These well waters, both from 
ordinary and artesian wells, are usually quite rich in the so-called alkali 
salts, but not in nitrates. 
These nitre spots occur in sections where these shales and sandstones 
do not occur, and consequently cannot be derived from them. These 
facts were known to us before we published anything upon the subject, 
and this process of elimination led us to the views adopted before we 
had any results of bacteriological experimentation at our disposal. If 
the alkalis and nitrates have a common origin they should have a com¬ 
mon distribution, but this is not the case even for very limited areas. If 
they owed their origin to leaching then the ground-waters found beneath 
these lands should contain notable quantities of nitrates, but this is not 
true and the nitrates are localized in the brown spots to such an extent 
that the people have made this characteristic the distinguishing one in 
their complaints. 
The nitrates might make the soil more hygroscopic but there is 
nothing in them per se to produce a color, but Azotobacter in the pres¬ 
ence of nitrates, do produce a brown, almost black, color. The brown, 
often almost black, color is characteristic of these spots and samples of 
soil taken only a little way, a few feet, from these brown spots, contain 
no unusual amounts of nitrates. This is true to such an extent that I 
believe it quite possible to collect samples within a few inches of one 
another, one of which may show only ordinary amounts of nitric nitrogen 
and the other from hundreds to thousands of parts per million. 
The burden of the complaints made is of “brown spots on which 
nothing will grow.” These spots have appeared in cultivated land, much 
of it otherwise very good land, not seeped nor saturated with alkali and 
not deficient in drainage. 
