6 The Colorado Experiment Station 
whole leaf had turned brown and was of course killed. Many trees 
died from this cause. Plate I shows leaves with burned edges. 
This trouble was not confined to any one section but was common 
to several sections of the state. While it, in all probability, de¬ 
pends upon soil conditions, these conditions are met with in so many 
places that it is necessary to consider the condition rather than the 
soil itself. It sometimes occurred in light and sandy loams and 
sometimes in clayey soils. It is sometimes in comparatively low lying 
lands, again in the lower lying portions of higher lands and again on 
hillsides. The road side, a ditch bank, and the cultivated fields rep¬ 
resent the range of places in which this thing may reveal itself. 
There is one thing common in all of its occurrences, namely, a 
brown color in the surface soil. This color is less marked in the 
sandy soils than in the so-called adobe soils. Perhaps this is due to 
the presence of deliquescent salts on the surface of the adobe soils, 
or more probably to the color of azotobacter films. 
The preceding gives in a very general way the big features 
of the question forming the basis of this bulletin. We have cer¬ 
tain soils, quite generally distributed throughout the principal sec¬ 
tions of the state, which develop what is popularly known as “black 
alkali” but the popular judgment in regard to the cause of the dark 
color is wholly wrong because they have adopted the term from 
California, where it has a fixed and definite meaning, which is not 
applicable to our case. While it is not advisable to do so we may 
occasionally use the term because these dark spots are designated 
by the people as “black alkali.” Nitre spots will, however, be used 
as the equivalent of the popular term “black alkali.” We have so 
far as is now known, no land, unless it is some near a peat bed, to 
which the term “black alkali” properly applies. 
Reports of black spots on which “nothing will grow” have 
been received at this department quite frequently during the past 
four years, and occasionally prior to that time. While at work in 
the San Luis Valley several years ago, my attention was called to 
what was supposed to be indications of petroleum. We drove 
through a small section of the country and observed quite a number 
of round, black spots absolutely devoid of vegetation, the surface 
was glistening and appeared as though wet. It was frequently the 
case that these bare areas were occupied by an ant hill but a great 
many of them were not. I mention this because I thought at first 
that the ants might have something to do with the color and ap¬ 
pearance of these spots, but there were too many spots without 
ant hills in order that this should hold true. 
Samples from the surface of these spots proved to yield 13.4 
per cent of their air dried weight to water, and on evaporation this 
soluble portion proved to be so deliquescent that it could not be 
