8 
COLORADO EXPERIMENT STATION 
but have extended it to include samples from widely separated and dis¬ 
tant localities in the United States. These have been designated as 
“foreign” merely to distinguish them from the local collection. With 
but two or three exceptions, as hereinafter noted, they have been gath¬ 
ered from cultivated land and represent cotton, tobacco, melon and 
orchard soils of the South, general farming and sugar-beet land of the 
East, Central and Middle West, the citrus and viniferous districts of 
the Southern Pacific Coast, and the orchard section of the Northwest. 
Their distribution was as follows: Two samples from Georgia, 
three from North Carolina, one from Virginia, one from Ohio, one 
from Arkansas, one from Kansas, two from Oklahoma, one from 
Texas, nine from California, and one from Washington. 
The samples from our own state have been taken from different 
localities over a continuous area of approximately six hundred square 
miles. Much of this is still good farm and orchard land but no small 
portion has been rendered worthless during the past five years by ex¬ 
cessive nitrates. The soils which we have selected are fair representa¬ 
tives of orchard land, sugar beet, oat and alfalfa fields, barren wastes 
and raw land in the afflicted district. A few samples from apparently 
normal localities have been introduced for comparison. 
METHODS 
Nitrifiable Substances Employed : 
Ammoniacal nitrogen for our experiments was supplied to the 
soils in three forms: Ammonium sulphate, ammonium carbonate and 
ammonium chk>rid. An additional series was prepared with dried 
blood in order to determine whether the ammoniacal nitrogen made 
from proteid nitrogen by the ammonifying bacteria would respond to the 
nitrifying agents to a greater or less degree than the above mentioned 
compounds of ammonium. The ammonium sulphate, ammonium chlo- 
rid and ammonium carbonate were added to the soils in the form of 
solutions so prepared that io c. cm. of each solution contained its re¬ 
spective salt in quantity sufficient to furnish ioo m. g. of nitrogen. 
Collection of Samples .—With respect to the collection of the for¬ 
eign samples, it was practically impossible either to expect or to secure 
any uniformity since the majority of the samples were taken by persons 
wholly unfamiliar with the technique of sampling, to say nothing of 
bacteriological precautions. To have imposed upon them the burden of 
sterilizing spatulas and containers would have meant not getting the 
soils; consequently, the only instructions which accompanied the re¬ 
quests were that the samples be taken to a depth of four inches and 
that about as much soil be sent as would go into an ordinary sized 
cigar box. The majority of collectors lined the boxes with paper be¬ 
fore putting in the soil, but some failed to do even this. Occasionally, 
a sample came to the laboratory in a heavy, paper sugar sack, and one 
was received in a cloth bag. 
For the benefit of any who may take exception to the results of 
our comparative studies on the ground that the foreign series 
