THE NITRIFYING EFFICIENCY OF CERTAIN 
COLORADO SOILS. 
By Walter G. Sacicett 
Introduction 
When our bacteriological studies of Colorado soils were begun some 
three years ago, the chief interest in the investigation centered about 
the occurrence and origin of certain “brown spots” in the soil. These 
had been observed as early as 1892, and by this time, 1910, they were 
becoming so common as to be identified readily by mere mention of 
their physical characters. 
One not familiar with their appearance might easily mistake the 
smaller areas for spots where crude oil had been spilled, especially if 
this material had been used for heating purposes in the orchard where 
they occurred. Sometimes the spots are sharp in outline and are limited 
to a space of three to five feet in diameter; again, tracts of one to five 
acres and more exist, which present an unbroken expanse of dark 
brown, wet-appearing waste land. A well defined crust is usually pre¬ 
sent, and while the surface appears wet to the eye, it is not necessarily 
so ; in fact, we often find it to be hard and dry. Beneath this crust, 
which may be one-half an inch in thickness, the soil is frequently mealy 
in texture. The same characteristic greasy, brownish-black color exists 
along the ditch banks, on the sides of the irrigating furrows and for 
miles in more or less broken stretches along the roadsides. 
The first complaint of serious damage to agriculture from this 
cause was received by Dr. Headden in 1905, who, two years later, began 
h : s studies of the niter soils of Colorado. The universal grievance of 
those who are attempting to 'cultivate land of this character is that 
nothing will grow on the brown areas; it matters mot whether the crop 
is sugar-beets, alfalfa, small grains, or fruit, all suffer alike. In look¬ 
ing over a field of oats or sugar-beets, one cannot fail to be impressed 
with the dark green color and rank growth of the plants which border 
the barren areas. This would seem to indicate the presence of a zone 
where conditions for plant growth are particularly favorable, beyond 
which they become almost intolerable. That such is the case has been 
demonstrated repeatedly by Dr. Headden. It suggests that where the 
growth is vigorous, the soil contains the optimum amount of nitrates 
for vegetative development; and where nothing can live, that the nitrates 
are in excess. Apple trees appear to have suffered more than any 
other of our fruit trees. In the fruit-growing sections of the state, 
these have died by the thousands, and acres of once valuable and profit¬ 
able land are now worthless. Heavy manuring, additional draining, ex¬ 
cessive irrigation and more thorough cultivation, all have been tried 
with the hope of ameliorating the pending conditions. Little or no 
benefit has accrued from these efforts, and up to the present time, 
we have observed nothing which seems to indicate a positive recovery, 
although, now and then, our attention has been called to cases where the 
intensity of the attack, as measured by the time required to accomplish 
