14 The Colorado Experiment Station. 
tolerance for the apple trees and they died. By May 3, 1911, this 
land, which showed no nitrate at this place in 1909, was brown 
and mealy and wheat was not able to grow healthily in it and on a 
great deal of the ground not at all. A surface sample, taken in 
May, 1909, from a part of this orchard where the trees had died, 
gave 4.68 percent soluble in water which contained nitric acid 
corresponding to 7.239 percent of sodic nitrate. A similar sample, 
taken in May, 1911, from ground which did not show this trouble 
in 1909, gave 6.80 percent soluble in water containing nitric acid 
equal to 12.621 percent of sodic nitrate. As these samples repre¬ 
sent the surface portion, approximately to a depth of two inches, we 
will compare them; in 1909 the surface two inches of a portion of 
this land where the trees had died contained 2,258.8 pounds of 
sodic nitrate per acre, whereas a portion of the same land which 
did not contain enough nitrates in May, 1909 to kill the trees con¬ 
tained in May, 1911, 3,433 pounds, a gain of 1,174 pounds per acre 
in the surface two inches in two years on the supposition that this 
soil was really as rich in 1909 as the ground in which the trees 
had already died, which is not true, so the gain actually exceeds 
1,174 pounds of nitrate in two years. Evaporation of ground 
waters from the surface of this soil is wholly inadequate to account 
for such an accumulation as this. I will give figures and state¬ 
ments showing that it is very liberal to assume the presence of 
0.3 p. p. m. of nitric nitrogen in the ground water and I will sup¬ 
port this with further figures in subsequent paragraphs. But 0.3 
p. p. m. of nitric nitrogen is equivalent to 1.8 p. p. m. of sodic 
nitrate equal to 4.896 pounds per acre foot. On the assumption 
that this nitrate has been brought to this land by the ground 
waters and deposited by its evaporation we would have to evaporate 
239.8 acre-feet in two years or 119.9 acre-feet per annum— 
whereas our actual evaporation from a free water surface is forty- 
one inches or it would take 70 years to effect the evaporation from 
a free water surface required by our supposition in two years from 
a soil surface. There is another feature of which we cannot lose 
sight; our ground waters are rich in other dissolved salts and these 
must be accounted for in some way. Our ground waters seldom 
carry less than 100 grains per imperial gallon or 1,429 p. p. m. or 
3,858 pounds per acre-foot of water according to which we would 
have to account for 925,920 pounds or 463 tons of alkalis on every 
acre of this ground which, assuming the alkalis to be as dense as 
the soil itself, would cover the soil one-quarter foot deep every two 
years which is evidently contrary to the facts. Our soils are rich 
in soluble salts, that is salts soluble in water, but they are not 
covered nor even mixed with any such quantities as this supposition 
shows must be present. This particular soil is quite rich but we 
found in the surface soil, two inches deep, in 1909, 4.68 percent and 
