THE FIXATION OF NITROGEN 
IN COLORADO SOILS 
By WM. P* HEADDEN 
f: It is now 8 years since our last publication under this title, 
i ‘The Fixation of Nitrogen in Colorado Soils”, appeared and the 
■ content of our previous publications on this subject may be un- 
known to some reader of this. It is therefore proper to give 
a concise statement of the principal points already presented 
in order that the relation of this bulletin to the general ques 
! tion may be evident. 
' Bulletins 155 and 178 present the facts relative to the 
occurrence of nitrates in our soils, often in very excessive quan- 
tities. This fact is established by many instances in which the 
amount of nitrates, usually given, as a matter of convenience, 
I as sodic nitrate, but sometimes as mixtures of calcic, magnesic, 
potassic and sodic nitrates in the statement of the analyses, 
; ranged from a few hundredths of one percent up to more than 
six percent of the air-dried soil. Twenty-seven separate oc- 
currences in soils and two in well waters were discussed in 
order to establish the fact that such occurrences are not simply 
! scientific curiosities and to show that their distribution is 
general throughout a very large territory. 
In these bulletins is also presented an explanation of their 
J formation. It was first shown by a process of elimination that 
these nitrates are not derived from the waters used for irriga- 
! tion nor from ground-waters. Further, that the very prevalent, 
^ popular view, that these salts are brought up from beneath, is 
not tenable. Further, that the facts in regard to the occurrence 
■ of nitrates in the rock strata do not permit us to assume these 
^ as the source of these nitrates. Further, that the manner of 
' these occurrences, often being confined to very limited areas, 
' and in such positions that we cannot explain them on the as- 
sumption that the nitrates have been concentrated in these 
' places by being washed out of other lands, indicate a local 
origin. Such explanations having been eliminated, we coii- 
i eluded that the occurrence of these excessive quantities of ni- 
trates were exaggerated instances of a process going on in our 
i soils, to wit, that these nitrates are being formed in the soil. 
I It was evident that these areas, at first designated as ^^spots” 
} because of their small size, — and this term, nitre-spots, was re- 
