The Fixation of Nitrogen in Coeorado Soils' 39 
owe their origin to the evaporation of this ground-water brought 
to the surface by capillarity, we have to answer the following 
questions: How long has it taken to do this? What has become 
of the associated salts which we know are readily moved through 
the soil by capillarity? In regard to the first question, we have 
only the testimony of the trees. They lived and grew healthily till 
the season of 1911. A few of them showed distress in 1910. 
These nitrates were not present in deleterious quantities at this 
place till the season of 1911, so the concentration must have taken 
place very rapidly. To furnish the amount of nitrates in the sur¬ 
face three inches of this land per acre would require the evapora¬ 
tion of 40.4 acre feet of water, which we found four feet nine 
inches below the surface. Can this be done in this time? Our 
actual evaporation is less than 60 inches per annum from a free 
water surface (it is 41 inches at Fort Collins) and the evaporation 
of 40 acre feet of water from the surface of this land would require 
about eight years, provided it presented a free water surface, but 
we found this free water 4^ feet below the surface. Further, what 
has become of the million pounds of other salts which this water 
holds in solution? This is not the only trouble. We find within 
60 feet of this, entirely different conditions. The ground-water is 
practically the same distance below the surface, if there be any 
difference the water is a little nearer the surface in the second case; 
but there on the same date, so that there is no question of weather 
conditions, we find 2 p. p. m. in the surface three inches which at 
a depth of 54 inches reaches 80 p. p. m. and the ground-water 
contains 318 p. p. m. of nitric nitrogen and 18,557 P- P- of total 
solids. Why is the surface portion so poor in nitric nitrogen and 
why do the nitrates increase with depth till we find the ground- 
water much richer than the soil ? The answer that I offer is that 
the late irrigation had washed these nitrates into the deeper por¬ 
tions of the soil and into the ground-water. While our conditions 
are involved and our data difficult to interpret, there is nothing 
to indicate that, in fact, these nitrates ever moved back to the sur¬ 
face. My conviction is that in the case of the first hole dug we 
selected a spot which had escaped with a light irrigation or with¬ 
out any. There was no reason why the people should be careful 
about the distribution of the water, as the trees were already dead. 
The nitrates found were those that had been formed there during 
the preceding season. The fact that these trenches had to be dug 
in slightly different places for the different sectional samples is 
unfortunate because a difference of two or four feet may make 
every difference as our surface samples, taken only a few feet part, 
fully demonstrate. 
