228 
the acidity and bringing about a condition favor- 
able for the growth of the nitrifying organisms. 
When ammonium sulphate or ammonium chloride 
was added to the soil there was no chance for a 
similar decomposition and the soils remained acid. 
Bacteriological Studies of the Fixation of Nitro- 
gen in Certain Colorado Soils: WautER G. 
SACKETT. 
The power to fix atmospheric nitrogen is a prop- 
erty common to many cultivated Colorado soils. 
This power is not confined to the fixation of 
nitrogen in solutions, but is manifested in soils as 
well. 
‘“‘The rate of fixation of nitrogen obtained is 
sufficient to account for the nitrates found in the 
soil provided that it is nitrified. The rate of 
nitrification obtained is sufficient to account for 
the formation of the nitrates found in most cases, 
if not all of them.’’ 
The nitrates formed are sufficient to destroy all 
vegetation, in one case amounting to 172 tons per 
acre in the surface five inches. 
The nitrogen-fixing power is not confined to any 
geographical locality or class of soils, however, the 
adobe shale soils, both in a raw state and when 
newly cultivated, possess little, if any, nitrogen- 
fixing power. 
Excessive nitrates either destroy or greatly at- 
tenuate the nitrogen-fixing flora of a soil. 
A limited amount of soil nitrate does not seri- 
ously affect the nitrogen-fixing power of a soil. 
Azotobacter chroococcwm appears to be the dom- 
inant nitrogen-fixing organism in the soils studied. 
The dark brown color of the niter soils is due, 
in a large part, to the pigment produced by Azo- 
tobacter chroococcum. 
Given a source of energy, the nitrate is the lim- 
iting factor in the production of the brown color. 
In the presence of nitrates, Azotobacter chro- 
ococcum develops a chocolate brown to black pig- 
ment; nitrites, in certain amounts, produce similar 
results, but to a less degree; nitrogen as NH,Cl, 
(NH,).SO,, asparagin, and peptone has no effect 
upon this function. 
The highly colored extracts obtained from cer- 
tain niter soils suggests that the pigment of Azoto- 
bacter chroococcum may be soluble in the alkaline 
soil waters. 
Excessive soil moisture, by interfering with the 
growth of Azotobacter chroococcum, prevents the 
formation of the brown color on the soil, and 
makes the fixation of atmospheric nitrogen im- 
possible. 
SCIENCE 
[N.S. Von. XXXV. No. 893 
Excessive irrigation, too diligent cultivation and 
the alkaline reaction of our soils appear to favor 
unduly the growth of Azotobacter. 
This paper is published in full as Bulletin 179 
of the Colorado Experiment Station, Fort Collins, 
Colorado. 
The Movement of Nitric Nitrogen in Soil: ROBERT 
STEWART and J. EH. GREAVES. 
In the work which has been conducted for eight 
years at the Utah Experiment Station upon the 
influence of irrigation water upon the production 
and movement of nitric nitrogen in the soil, there 
has been observed a variation in the nitric nitrogen 
content of the soil and the concentration of the 
soil solution with the water applied, the crop 
grown and with the season. 
The soil upon which these investigations have 
been conducted is ideally adapted both chemically 
and bacteriologically to support a rapid bacterial 
action, yet the amount of nitric nitrogen present 
to a depth of ten feet does not exceed three hun- 
dred pounds per acre. 
Deposits of nitrates do occur in the country 
rock in widely distributed areas in western 
America. 
The careful analytical work reported by Dr. 
Headden on the composition of Colorado soils indi- 
cates a close relationship between the nitric nitro- 
gen and chlorine content of these soils, indicating 
clearly a common origin of these two elements. 
The Present Status of Soil Inoculation: Karu F. 
KELLERMAN. 
The method of pure-culture inoculation is less 
certain than the use of soil from old well-inocu- 
lated fields, but has, however, the advantage of 
cheapness and greater ease of transportation and 
application, as well as the important advantage of 
the absence of introducing weeds and plant dis- 
eases. The crown-gall disease of fruit trees is the 
most conspicuous example of disease which may 
be disseminated by soil transfer. 
Reports received from farmers who have con- 
ducted inoculation tests with cultures distributed 
by the Department of Agriculture during the past 
seven years give an average of 76 per cent. success 
and 24 per cent. failure, if only those reports are 
considered that make possible some determination 
regarding the action of cultures. If previously 
inoculated fields, crop failures and such other 
doubtful cases are included with the failures our 
percentage of success for this same period is 
reduced to 38. 
