96 
The: Colorado Expe:riment Station. 
In some sections practically the whole of the irrigated land has been 
affected, thus eliminating the question of transportation except as to the 
river water used for irrigation. Our river waters carry from 0.00 to 0.4 
part per million of nitrogen as nitrates. 
The localization of these areas and the rate of increase also preclude 
the theory of transportation and concentration. 
Excessive irrigation for the purpose of washing out the “black 
alkali,” nitrates, has not been successful, but this failure has probably 
been due to the method used. 
The liberal application of manure has not given permanent, if indeed, 
any relief. 
Thorough and frequent cultivation has not been followed by the 
beneficial results expected. 
The soils of Colorado are, generally speaking, poor in nitrogen, but 
the ratio of nitric nitrogen to the total nitrogen is frequently very high, 
17 to 5 0 percent being not uncommon. 
The nitrogen in these soils is fixed by azotobacter which use the 
nitrogen in the air to build up their tissues. 
The fixation of nitrogen, in a sample of ordinary soil from the College 
farm, collected December 12, 1910, on incubation for twenty-seven days, 
was found to have taken place at the rate of 5,222 pounds of nitrogen, 
equal to 17.5 tons of proteids per acre-foot of soil per annum. 
The nitric nitrogen present in this soil at the beginning of the ex¬ 
periment corresponded to 8 40 pounds of sodic nitrate per acre-foot of 
soil; this had increased in 4 8 days to 1,9 9 9 pounds as a maximum, a gain 
of 1,15 9 pounds which would give, if this rate were continued for a year 
of three hundred and sixty days, a gain of 8,676 pounds, or four and a 
third tons of nitrates per acre-foot of soil. 
The incubated samples, with but one exception, showed a darkening 
of their surfaces. 
No addition of anything except boiled, distilled water was made to 
these samples before or during incubation. A large bottle was partially 
filled with some, approximately eight pounds, of the original sample just 
as it was collected. This bottle was loosely stoppered, inverted and kept 
in a room where the temperature was fairly high and even. This soil 
was analyzed just as the incubated samples were and showed a decided 
increase in both the total and nitric nitrogen, 7.45 and 19.15 percent re¬ 
spectively. 
Fixation takes place rapidly in this soil in the presence of from 13.5 
to 20 percent of water. The rate of fixation of nitrogen obtained is suffi¬ 
cient 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 brown color of these soils is due to pigments produced by the 
azotobacter. 
