THE AMMONIFYING EFFICIENCY OF CERTAIN 
COLORADO SOILS. 
By Walter G. Sackett. 
INTRODUCTION. 
In a former bulletin (i) the writer has called atten¬ 
tion to the power of many cultivated Colorado soils to fix atmospheric 
nitrogen through the agency of Azotobacter, both in the soil and in 
irrannite solutions. The investigation referred to was undertaken for 
the purpose of determining the source of the nitrogen from which the 
excessive nitrates, present in some of our soils, might have been de¬ 
rived. The results of this work point clearly to the atmosphere as the 
source of the nitrogen and to Azotobacter as the medium by which it is 
transformed from a gaseous into a proteid form, and subsequently 
transferred as such to the soil. 
With an ample and reasonably constant supply of protein thus 
assured, our efforts have been directed, more recently, toward a study 
of the transformation of the combined nitrogen into ammonia the first 
step in the formation of nitrates from the complex nitrogen molecule. 
In the present investigation, we have determined the ammonifying effi¬ 
ciency of some thirty Colorado soils, many of which are known to be 
affected with the niter trouble. I use the term ammonifying efficiency 
in the sense in which it has been employed by Stevens (2), to de¬ 
note not only the presence of ammonifying organisms in the soil which 
are capable of exercising their specific function under favorable condi¬ 
tions, but also the suitability of the soil as a medium in which the pro¬ 
cess of ammonificaton may proceed advantageously. 
The soils under examination have been collected from a wide range 
of territory representing orchard land, sugar beet, oat and alfalfa fields, 
barren wastes and raw land. They include a variety of soil types, and 
almost all have been under cultivation and irrigation at one time or an¬ 
other. 
The proteid nitrogen for our experiments has been supplied in four 
different forms :—Cottonseed meal, dried blood, alfalfa meal and flax¬ 
seed meal. These have been employed rather than soluble forms such 
as peptone and gelatin since the latter could not be used in a practical 
way under field conditions, and, furthermore, the results obtained from 
substances of this kind would be of little practical value outside of the 
pure scientific interest attached. On the other hand, by making use of 
some of the more common nitrogenous fertilizers, we have been able 
to learn something of the avai'ability of the nitrogen in these materials 
(1) Bacteriological Studies of the Fixation of Nitrogen in Certain Colorado Soils. 
Bui. 179 Colorado Experiment Station, 1911. 
(2) Stevens, F. E. and Withers, W. A., Studies in Soil Bacteriology III. Con¬ 
cerning methods for determination of nitrifying and ammonifying powers. Cent. f. Bakfr. 
Abt. II., Bd. 25, No. 1-4, p. 64, 1909. 
