The Fixation of Nitrogen. 83 
I have been unable to find any more satisfactory data relative 
to the amount of nitric nitrogen in soils than was given in Bulletin 
155, P a £ e 3 7 , based upon Rothamsted results which showed that 
in lands cultivated as bare fallow about 80 pounds of nitrogen 
were converted into nitrates in 14 or 15 months. This includes 
the nitric nitrogen removed in the drain waters. If this amount 
were all present at one time and contained in the surface foot of 
soil it would amount to only 0.002 of one percent. In the top 18 
inches of another field they found in September and October 49 
pounds of nitric nitrogen. If this were all contained in the surface 
foot at a given time it would correspond to 0.001225 percent. The 
statement is made that this large amount is due to the richness of 
the soil in nitrifiable matter, showing that 49 pounds per acre to a 
depth of 18 inches was considered high, if not unusual. The ratio 
of the nitric nitrogen to the total nitrogen at any time is not given. 
It is well known that the nitric nitrogen present in soils varies 
from time to time owing to several causes, but the easy solubility 
of the nitrates makes it very probable that the amount of them 
in the surface soil will be dependent upon the amount of rainfall 
and the time which has elapsed between the last rainfall and the 
taking of the sample. The character of the soil, i. e., the readiness 
with which it allows water to pass through it, its power to retain 
the nitrates, and the evaporation which takes place from its surface 
will also influence the amount of nitric nitrogen present at a given 
time. Rainfall does not usually play the important part with us 
that it does in England or in the eastern states; if it ever does, it 
is only for short periods of time. 
The samples of soils used for the determination of nitric nitro¬ 
gen in Bulletin 155, pp. 38 and 39, were taken at the close of a 
wet season, that is, for Colorado. We had had 3.36 inches of rain¬ 
fall between September 12 and December 1, and .47 inches during 
the month of December, and yet we found a maximum of 320 
pounds of nitric nitrogen in a set of 46 samples taken between Octo¬ 
ber 1 and 15. The samples were taken to a depth of six inches. In 
another set of 54 samples taken January 26-31, we found a maxi¬ 
mum of 280 pounds of nitric nitrogen in the top six inches of soil. 
It is to be remembered that these samples were from fields which 
had been planted to beets. The last sample was taken from the 
turn row. These quantities are so materially higher than those 
given for Rothamsted soils, though these Rothamsted fields had 
been cultivated as bare fallow, that we can scarcely compare them 
at all. In the case of the 80 pounds of nitric nitrogen per acre in 
the Rothamsted soils the nitric nitrogen removed by drainage has 
been determined and included. In these Colorado samples only the 
nitric nitrogen which was present in the soil to the depth of six 
