82 The Colorado Experiment Station. 
suits from this operation. Perhaps frequent and repeated flooding 1 
combined with drainage, where needed, might prove effective. 
If the nitrates are not present in the various geological strata 
and there are no local deposits scattered all over large sections of 
the state in which we may find the source of these nitrates oc¬ 
curring in our soils, the question, Whence do they come? is 
germane. 
The facts stated in connection with Case No. 8 are, I believe, 
perfectly applicable to all other cases and it can be stated, without 
any material modification, that these nitrates are not the product of 
concentration of ground waters flowing from other lands as they, 
these ground waters, contain no nitrates; neither did the soil, ex¬ 
amined to a depth of three feet, nor the white or common alkali 
which was abundant on this adjacent land contain any nitrates in 
1907. Further, they are not due to the concentration of surface 
washings. 
There is one remote possibility, which so far as I know, has not 
been suggested, i. e., the water used for irrigation. While this is 
an extremely remote possibility, we can answer the suggested 
question. We have sanitary analyses of several of the river waters, 
also of reservoir waters, which are used for the purposes of irri¬ 
gation, and the nitrogen present as nitrates varies from a trace to 
0.400 part per million, a quantity not only too insignificant to be 
considered a factor in the problem, but so nearly zero that it shows 
that there are no nitrates in the rocks of the drainage areas of 
these rivers to which the nitrates may be traced. 
The answer that I suggested in Bulletin 155 was that these 
nitrates are formed where we find them. That the nitrogen is 
taken from the atmosphere by azotobacter and is subsequently 
changed into nitric acid, respectively nitrates, either by the azoto¬ 
bacter themselves or by other bacteria. So far in this bulletin f 
have presented facts in abundance to establish the occurrence of 
very large quantities of nitrates in certain of our soils, and that the 
concentration in hundreds—I am fully justified in saying thous¬ 
ands—of instances, is most remarkable, but all proof adduced bear¬ 
ing upon their origin has been by a process of exclusion, i. e., the 
nitrates are present but they have come from nowhere, therefore 
they are formed in situ. 
In Bulletin 155 I showed by nearly 300 nitrate determinations 
that many of our soils contained very notable quantities of this 
substance. At the time these determinations were made, October, 
1909, we found this quantity varying from 12 to 1,920 pounds per 
acre in the top six inches of soil, calculated as sodic nitrate. These 
samples were from cultivated fields in good condition which had 
been planted to beets. The highest results were obtained in the 
turn rows. 
