Alkalis In Colorado 
27 
be pretty hard to explain how the nitrates, if they came from any such 
source, could collect in a spot, perhaps not more than 2 feet in diameter, 
in the middle of a field, or right at the edge of a river bank. I have 
stated that the nitrogen is present in the spots in greater quantities 
than in the soil just outside of them, also that the water that flows 
under them from outside land does not contain them. 
Micro-organisms Fix Atmosphere Nitrogen 
After I had studied a great many spots and tried to find some 
source for this nitrogen and could find none, the atmosphere forced 
itself on me as the only source from which the nitrogen could come. 
In short, it is well known that there are micro-organisms that in grow¬ 
ing, take their nitrogen directly from the air and do not have to have 
some other plant to help them grow. The organisms that make the 
warty bunches on the roots of pea-vines, tubercles, in some way make 
the atmospheric nitrogen available to the pea, but these organisms can¬ 
not grow without the pea and the pea cannot use the atmospheric nitro¬ 
gen without the organisms ; nevertheless, they are said to fix the nitro¬ 
gen, though they have to have help. There are other organisms, really 
plants, so small that we have to magnify them a great many times be¬ 
fore we can see them, which can use the nitrogen of the air to build up 
their bodies. If we grow these in a soil fitted for them, these organisms 
add nitrogen to it even when there is no nitrogen in it to begin with, 
because in growing they take nitrogen from the air. We say that they 
fix it and call the process fixation. This process is going on in our 
arid soils much more freely than in most soils and in these ‘‘brown 
spots” these organisms have been very active and gathered a great deal 
of nitrogen. 
These organisms die like other plants and, when dead, their nitro¬ 
gen travels the same way that all other organic nitrogen travels. It is 
made the prey of changes that result in the formation of nitrates and 
when these nitrates get strong enough they kill out the nitrogen-fixing 
organisms themselves. We have found these organisms very abundant 
in some spots and have grown them and had them fix nitrogen rapidly, 
and in others we found them nearly all dead, at least, we judged them 
to be dead for they would not fix nitrogen, while their living neighbors 
from the outside of the spot fixed it very vigorously. We may say, 
then, that the nitrates are formed in these spots where we find them. 
The only really new thing in this explanation is the claim that these 
organisms carry on these processes on a big enough scale to produce 
these conditions that we find. We have shown that they can fix, under 
favorable conditions, enough nitrogen in i acre foot of soil to form 
163/2 tons of sodic nitrate if it were all converted into this form. This 
result is far beyond anything that we have found in our fields, so these 
organisms, Azotohacter, are not called upon to maintain this record all 
