The Fixation of Nitrogen in Colorado Soirs 35 
till we encountered water. From these sections samples were taken 
forming' a continuous section, usually to a depth of fifty-five inches, 
but the maximum depth to which any set of samples was taken was 
sixty-seven inches. There were also other samples taken, especially 
samples within the “brown spots’" mentioned as occurring as dis¬ 
tinct spots in some portions of this land; and others taken just out¬ 
side of these spots; also some of the ground-water. The condi¬ 
tions in 1912 were better than in 1911, and we found only moder¬ 
ate quantities of nitrates in 1912 in sections of this land in which 
they were very evident in 1911. 
I raised the question in Bulletin 155 in regard to the amount 
of nitric nitrogen that we may expect to meet with in good, culti¬ 
vated soils, especially in the surface portions. We concluded that 
in general from five to eight parts per million would be found to 
be a usual maximum, but that 30, 40, and 50 are not unusual 
amounts to find in our lands, particularly if fallow. We also found 
like quantities in cropped land absolutely free from seepage. In 
cultivated fields we have found 120 to 160 and 200, and have shown 
that the amount may vary in a cultivated field up to 330 p. p. m. 
I do not think that the finding of from 30 to 50 or more p. p. m. of 
nitric nitrogen in alkali incrustations, which usually means the soil 
and effloresced alkali scraped up together off of the surface of the 
land, is at all significant of the association of the nitric nitrogen 
and alkali, for we find such amounts in land which we would con¬ 
sider entirely free from alkali. 
The distribution of the nitre in the surface-portions of the land 
is set forth by series of composite samples, each composite sample 
consisting of 60 sub-samples. The sample from the alfalfa field was 
likewise a composite sample of about 20 sub-samples, but these were 
taken from the surface with a shovel and not with a soil tube. 
These samples give a section of the land selected beginning with the 
alfalfa field and crossing- the area of active fixation and nitrifica¬ 
tion, to a section where, in 1912, it was very moderate, perhaps no 
more than normal, for our lands. 
This section, beginning with the alfalfa field, shows 20 to 8c 
p. p. m. of nitric nitrogen, reaches a maximum of 367 p. p. m., and 
then passes to a minimum of 3 p. p. m. We find that the surface 
three inches carry by far the larger part of these nitrates. The 
alfalfa land sampled was free from vegetation, but was quite 
strongly alkalized. The orchard land was not strongly alkalized, 
but the brown color, due to the Azotobacter pigmentation, 
could be traced with the greatest ease and detail in 1911 
throughout this land. In 1912 this was the case only in portions of 
it, and these portions are as clearly designated by the analytical re- 
