the: nitrifying efficiency of certain Colorado soils 
43 
2. Colorado soils possess a vigorous nitrifying flora. 
3. The nitrifying flora of the Colorado soils is distinct from that 
found elsewhere; it is either made up of entirely different organisms, 
or, if the same organisms, they have become so changed by their en¬ 
vironment that they behave like different strains. 
CONCLUSIONS 
Many cultivated soils of Colorado contain a vigorous nitrifying 
flora capable of transforming ammoniacal nitrogen into nitrate nitrogen. 
Both our normal soils and those in the incipient stage of the niter 
trouble possess this power in a very marked degree. 
Compared with soils from twenty-two other localities outside of 
the state, the Colorado soils examined are very superior in nitrifying 
efficiency. 
The nitrifying efficiency of Colorado soils bears an inverse re¬ 
lation to that of the foreign soils when referred to ammonium sul¬ 
phate. ammonium carbonate and dried blood as the nitrifiable sub¬ 
stances. 
Colorado soils produced their highest average gains in nitric 
nitrogen from (NhLL-SCh; the next largest from (NH^COs and 
the lowest from dried blood. The- foreign soils produced their largest 
average yields in exactly the reverse order. 
The nitrifying flora of the Colorado soils is distinct from that 
found in the majority of the foreign samples; it is either 
made up of entirely different organisms, or, if the same organisms, 
they behave like different strains. 
Excessive nitrates do not appear to interefere seriously with 
nitrification provided the chlorin is low. 
Excessive chlorin, with or without excessive nitrates, inhibits 
nitrification. 
Active nitrification takes place in the brown crust from the 
niter spots provided the chlorin is not excessive. 
The sample of raw adobe clay examined was deficient in nitrify¬ 
ing efficiency. 
The results of this study together with those of our two previous 
investigations justify the position that the excessive nitrates present 
in certain Colorado soils have resulted from the combined action of 
nitrogen-fixing, ammonifying- and nitrifying organisms. 
A CIC NOW L EDG M E NTS 
I beg to acknowledge my indebtedness to* the following persons 
for their courtesy in sending me samples of soil from localities out¬ 
side of Colorado: Professor Hugh G. Faust, Miss Ida Wray Fergu¬ 
son, Dr. E. B. Fred, Mr. C. C. Hommon, Dr. J. Y. Knapp, Professor 
F. B. Paddo-ck, Mr. Joe F. Pool, Professor F. S. Porter, Mrs. S. 
Ranne, Mr. G. C. Ramie, Mr. W. C. G. Sackett, Professor G. F. 
Searcher, Dr. Mary Wetmore, Mr. Charles F. White, Mr. J. Y. Whit¬ 
taker. 
