The Fixation oe Nitrogen in Colorado Soils 15 
which the “brown spots” showed only 87.6 times as much chlorin as 
nitric nitrogen in one case and 15 times as much in the other case. 
When one considers the fact that the sodic nitrate is more than 
twice as readily soluble as the chlorid and attracts moisture quite 
readily while the nitrates of calcium and magnesium are deliquescent, 
any concentration of these quantities of nitrates from such waters is 
wholly out of the question. Furthermore, these data show that any 
ratio given for the nitric nitrogen to the chlorin is utterly valueless. 
The question of how much nitric nitrogen do ordinarily good, 
cultivated soils in Colorado contain, can properly be raised in this 
connection. I endeavored to answer this question in Bulletin 155, 
pages 33-35. I think that from 5 to 8 parts per million of the dry 
soil may be considered as maximum quantities under ordinary con¬ 
ditions. This is for samples taken to a depth of two inches and not 
after heavy rains or recent irrigation. If the samples be taken to 
greater depths it will usually be lower, provided the moisture con¬ 
ditions are the same. According to this the first alkaline soil given 
carried rather large amounts of nitric nitrogen in three out of four 
cases, 12, 19 and 36 p. p. m., but the second soil carried no unusual 
amounts. The brown spots from the respective sections, however, 
carried 3,462, 494.0, 884.0 and 4,203.0 p. p. m... of nitric nitrogen... 
Apropos to the chlorin in ordinarily good, cultivated soils I 
have no data pertaining to samples taken to depths of only two or 
three inches, but I have quite a number of soil samples taken to depths 
of front one to three feet; these indicate that the chlorin in such 
soils under favorable conditions varies between 200 and 900 p. p. m., 
but in alkali soils whether nitrates be present or not the surface 
portions may be very rich in chlorin. I have a surface sample of 
soil from an orchard which was in fairly good condition but the 
trees, though apparently healthy, were small. The chlorin in this 
sample amounted to 1.5 percent of the dried soil or was 15,000 
p. p. m. There was no incrustation on this soil, but it was dark, 
due to the large amount of chlorids present, among which was a 
large proportion of calcic chlorid. There was only a trace of nitric 
nitrogen in the aqueous extract of this soil, corresponding to such 
quantities of nitric nitrogen as we would expect to find in any ordi¬ 
nary soil. Further, the samples of alkali soils already given show 
that we may have very considerable amounts of chlorin occurring in 
the surface portions without any nitrates. In the case of the alkali 
previously given the chlorin amounted to 261,000 p. p. m. and there 
was no nitric nitrogen. It is often, but not always, the case, that 
we find large amounts of chlorin in such samples as are rich in 
nitrates and the same thing is true of the sulfates. That the chlorids 
are not always high when the nitric nitrogen is high is shown by 
