THE FIXATION OF NITROGEN IN SOME 
COLORADO SOILS. 
By WM. P. HEADDEN. 
It has often been claimed that “black alkali" exists in Colo¬ 
rado. This idea has arisen because of the existence of certain 
black or brown spots which are met with in some localities. The 
color of these spots is not due, as has been supposed, to the presence 
of sodic carbonate, to which the name of black alkali has been ap¬ 
plied, but to other causes. This salt, sodic carbonate, constitutes a 
very small percentage of our alkalis and occurs in but one section in 
such quantities as to be injurious to vegetation. There are several 
independent occurrences of this salt in the section alluded to, but 
they are close together and are within an area of a few hundred 
acres. This occurrence has nothing in common with that of our 
alkalis, it is not disseminated through the soil but constitutes lake^ 
of sodic carbonate, small ones, it is true, but real lakes having ap¬ 
parently no connection whatever with the surrounding country. The 
source of this sodic carbonate is without doubt certain underground 
waters and has nt> direct relation to the formation of carbonates 
in semiarid countries. The soils of Colorado do not contain any 
deleterious quantities of this salt and the so called alkalis seldom 
contain any large percentage of it. The composition of Colorado 
alkalis has been a subject of investigation practically all of the time 
for the past fourteen years or more and it is pretty well established 
that there is but one type of alkalis in the State and that this is the 
white alkali, namely, a mixture of sulfates with some chlorids and 
carbonates, the latter ranging from nothing to io or n per cent. 
We have some variations based on the respective bases which may 
be predominant. The term alkali is used to designate any and all 
efflorescent salts which form white coatings on the soil or the 
grass, sticks, etc., which happen to be present and protrude from 
the surface. The popular term does not take cognizance of the 
chemical distinction made between alkalis and alkaline earths and 
the term is here used in its popular and readily understood sense. 
In some places, due to easily recognized conditions, we have almost 
pure calcic sulfate, in others, sodic sulfate, and in one rather large 
section magnesic sulfate is very abundant. We have no type in 
which either sodic chlorid or sodic carbonate can be said to be really 
abundant. We have examined some soils with the express purpose 
of trying to find out whether it would be reasonable and right to 
attribute their unproductiveness to the presence of salt, sodic 
chlorid, but no justification for such a conclusion has been found 
except possibly in two cases. The soil samples chosen were such as 
were believed to possibly owe their unproductiveness to this cause. 
