UTAH ACADEMY OF SCIENCES 97 
NITROGEN FIXATION BY BACTERIA IN UTAH SOILS. 
By E. G. PETERSON AND E. MOHR. 
(Summary). 
Undoubtedly much of the fertility of western soils is due 
to the action of soil bacteria, molds and fungi. This state- 
ment receives further verification from the following inves- 
tigation. 
Samples of soil from which the organisms here des- 
cribed were isolated were taken weekly from January 9th 
to November 4th, 1912, thus including representative cli- 
matic seasons. The Greenville Experiment Farm was used 
in this test, Plot 47. One hundred c. c. portions of mannite 
solution were inoculated with ten grams of soil and incu- 
bated at 10 degrees C. After ten days’ incubation sub- 
cultures were made in mannite solution and were incubated 
for ten days at 20 degrees C. Plates were made from these 
sub-cultures, and isolations of pure cultures were made 
from the plates. 
RESULTS. 
Several types of bacteria were found but only three 
appeared that grew readily and for a long period. These 
three types are briefly described in the paper. 
Type No. 1 appeared in the samples on the following 
dates: Jan. 9, 16, 22, 31, Feb. 7, 14, 21, 28, March 7, 14, 20, 
April 3, 10, 24, May 1, 8, 15, 22, 29, June 5, 19, July 21, 28, 
Aug. 4, 11, 18, Sept. 7, 14, 21, 28, Oct. 28, Nov. 4. 
Type No. 2 appeared on April 24, May 1, May 29, June 
12, June 19, Sept. 7. 
Type No. 3 appeared on Jan. 16, March 7, April 10, 17, 
May 1, 8, 15, 22, 29, June 5, July 12, Aug. 4, 25, Sept. 21, 
Oct. 14, 21, Nov. 4. 
5.335 milligrams of nitrogen, the most valuable element 
of the soil, were fixed in twenty days by type No. 1. 
5.616 milligrams of nitrogen were fixed in twenty days 
by type No. 2. 
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