30 
Colorado Experiment Station. 
of which time samples were removed for analysis and the total nitrogen 
determined. This showed a gain of 10.54 m. g. of nitrogen per 100 
grams of soil for the 27 days. 
I am indebted to Dr. Headden for the following results: 
Total nitrogen at the end of 27 days - 117.79 m. g. per 100 g. soil. 
Total nitrogen at the beginning, - 107.25 m. g. per 100 g. soil. 
Total nitrogen gained by fixation 
in 27 days,_:_10.54 m. g.per 100 g. soil. 
Assuming that the fixation, under field conditions, proceeds uni¬ 
formly at this same rate for six months, it would mean an addition 
of 475.26 pounds of nitrogen or 2,970.41 pounds of protein per month 
for every acre foot, and in six months, this would amount to 2,851.60 
pounds of nitrogen or 17,822.50 pounds of protein, while in a year, 
we should have 5,703.20 pounds of nitrogen or 35,645.00 pounds of 
protein per acre foot. With this increase of 2.85 tons of nitrogen 
or 17.82 tons of protein per acre foot in one year, there certainly need 
be no cause for anxiety over a source of nitrogen for high nitrate 
formation. 
Central Sample. 
This soil was collected by the writer December 30, 1910, and was 
from the same source as the sample designated as No. 29 of the pre¬ 
ceding series. The soil was first air dried and then passed through a 
40 mesh wire screen. The moisture was determined and found to be 
2.1 per cent. Sufficient sterile distilled water was next placed in a 
deep culture dish (100 m. m. x 30 m. m.) to give 100 grams of the 
air dried soil a water content of 10 per cent. 100 grams of the soil 
were next added to the water in the culture dish and the weight of the 
whole was determined. This weight was kept constant by daily addi¬ 
tions of sterile distilled water throughout the experimental period. 
The soil was incubated in the dark at 28°C. to 3 O°0. for thirty days at the 
end of which time samples were removed and the total nitrogen de¬ 
termined. For every 100 grams of soil there was an increase of 8.22 
m. g. of nitrogen in thirty days. 
Total nitrogen at the end of 30 days, - - 82.11 m. g. per 100 g. soil 
Total nitrogen at the beginning, - - - 73.89 m. g. per 100 g. soil 
Total nitrogen gained by fixation in 30 days, 8.22 m. g. per 100 g. soil 
Considering that the fixation, under field conditions, proceeds 
uniformaly at this same rate for six months, it would mean an additon 
of 333.60 pounds of nitrogen or 2,085.00 pounds of protein per month 
for each acre foot, or in six months this would amount to 2,001.60 
pounds of nitrogen or 12,510.00 pounds of protein, while in one year 
we should have 4,003.2 pounds of nitrogen or 25,020.00 pounds of pro¬ 
tein. Expressing this in tons per acre-foot per annum, we get an in¬ 
crease of 2.001 tons of nitrogen or 12.5 tons of protein. 
