94 The Colorado Experiment Station. 
we know to be caused by the azotobacter. I believe, and this 
belief is based upon tentative facts, that the azotobacter are at the 
same time nitrifiers, i. e., that the possess a double function which 
I believe has already been asserted but not generally accepted. I 
will state that Professor Sackett is not in any way responsible for 
this view and I do not know his attitude on this specific subject. 
These matters of theory and function are open ones but the fact of 
fixation of nitrogen and the formation of nitrates in our soils to 
such an extent as to kill fruit trees and ruin the land are estab¬ 
lished ones. 
I expect to present another bulletin in the immediate future 
dealing with another phase of the subject, i. e., the general effects 
of the nitrates upon the sugar beet, which will also continue these 
soil questions. 
SUMMARY 
The problems presented involve the occurrence of nitrates in such 
unusual quantities, that I may say, I hope without offence, that even the 
oldest and most experienced men have not seen the equal of it and have 
no conception of the facts. 
These nitrates occur so abundantly on very many square miles of 
otherwise good land as to be either prejudicial or fatal to vegetation. 
The apple tree has practically been adopted in this and preceding 
bulletins as the criterion whereby to judge of the intensity and extent of 
the injurious effects of the nitrates, though other trees and crops, espe¬ 
cially the sugar beet, have been mentioned. 
The damage done to apple orchards in this state is very serious. If 
we should estimate the trees killed within the past two years as equivalent 
to six hundred acres of orchard I believe that it would be a conservative 
estimate. 
These injurious effects of nitrates in cultivated soils are so new and 
so extensive that we cannot wonder that the layman or even the scientific 
man who has not seen them, fails to grasp them as facts or if they do and 
realize their importance, that they hesitate to acknowledge it. 
The trees all die in the same manner. This applies to the apple, pear, 
peach, apricot, willow, elm, cottonwood and other poplars, and to vegeta¬ 
tion in general. 
Experiments were made with sodic nitrate by applying it to apple 
trees, when it produced the same effects on the leaves and killed the trees 
in the same manner as these orchard and shade trees are observed to die. 
This series of experiments, eight of them, was not repeated because 
the results were concordant and conclusive. Experiments were also made 
using sodic chlorid, common salt, in sufficient quantities to injure the 
foliage. The effects were unlike and easily distinguished from those 
produced by sodic nitrate. 
The manner of attack, the effect produced and the very rapid termina¬ 
tion of the trouble in the death of the trees indicate the action of the 
same cause. 
The identity of these effects with those produced by sodic nitrate, and 
the presence of very unusual quantities of nitrates in all of the soils 
where this trouble is met with are accepted as conclusive proof that the 
nitrates are the cause of it. 
No attempt has been made to determine the limit of tolerance of the 
apple tree or other plants for nitrates. It has, however, been observed 
that an established beet plant can endure immense quantities of them, 
but not without deterioration in quality. 
The problems presented are not those of ordinary alkali, nor of 
seepage, nor yet of the occurrence of nitrates produced in the soil by 
