10 
Colorado Experiment Station. 
DISCUSSION OF THE SOILS UNDER STUDY. 
Nitrogen Fixing Power in Solution. 
In order that the reader may have a truer appreciation and a 
clearer conception of the actual conditions as they exist in the soils 
about to be described, it has seemed desirable to the writer to accom¬ 
pany each with a brief description of the field or orchard from which 
the sample was obtained. In several instances, the quantity of nitrate 
found appears to be in excess of all reason, but when measured by the 
damage done to vegetation, it falls easily within the limits of possibil¬ 
ity. d he converse of this proposition is equally true. If we are to 
witness the destruction of a forty-acre orchard in one season, we shall 
need to look for some such powerful agent as nitre occurring by the 
tens of tons to the acre foot. 
Samples Nos. i, 2, 3, 4. 
It is needless to say that at the beginnig of our work we encoun¬ 
tered unforeseen difficulties. We were dealing with soils which were 
decidedly unlike other soils, and in which previously unheard of con¬ 
ditions maintained. Naturally, our first samples were taken from 
those spots where the trouble was unmistakably present, and there was 
nothing to tell us how concentrated the nitrates might become and still 
permit the growth of the soil flora. The results obtained with these 
early samples were rather disappointing inasmuch as they seemed to 
possess practically no nitrogen fixing power when tested out in man- 
nite solutions. Subsequent work, however, showed that the nitrogen 
fixing bacteria, as well as the higher forms of plant life, had been de¬ 
stroyed by the nitrates. 
After a little experience we were able to establish, in a general 
way, a relation between the appearance and the nitrate content of a soil, 
on the one hand, and the probable occurrence of Azotobacter on the 
other. This made it possible to take samples more intelligently and 
to avoid the extremely high nitre areas. Samples 1, 2, 3 and 4 will 
>ei\e very nicely to illustrate the relation of nitrate accumulation to 
the presence of the nitrogen fixing bacteria. They were collected 
September 21, 1909. 
All four of these were taken from a forty-acre tract, twenty 
acres of which had been in bearing orchard and the remainder in al¬ 
falfa. In 1907 barren spots began to appear in the alfalfa; brown 
patches, here and there, in the orchard soon became conspicuous, and 
the trees commenced to die. By 1909, fifty per cent of the orchard 
had perished along with the entire twenty acres of alfalfa, and in 
1910, portions of possibly six rows along one edge and a few trees in 
a far coiner were making their last struggle. The whole center was 
a barren waste with not a weed to be seen. The greater part was 
brownish black on the surface, glistening with crystals and to all ap¬ 
peal ances wet, but, in fact, covered with a hard, dry crust about 3-16 
inche> thick. Beneath this, the next iU to 3 inches were mealy in 
