The Fixation oe Nitrogen in Coeorado Soils 19 
SAMPLES FROM THE SECOND PLACE CHOSEN. 
The samples from this place are all surface-samples, namely 
none of them were taken to a greater depth than three inches. Other 
samples from this place, taken to a depth of three feet, have already 
been given. The samples here presented are composite, taken to 
represent a fairly large surface. 
ANALYSES OF SAMPLES FROM SECOND PLACE CHOSEN. 
Samples taken April 4, 1912. 
Nitric Nitrogen Total Nitrogen Chlorin 
1 8.0 1,196.8 18,273.0 
2 16.0 992.8 19,180.0 
3 30.0 1,312.4 19,560.0 
Sample taken May 13, 1912. 
4 6.0 680.0 19,296.0 
Samples taken July 10, 1912. 
5 29.0 1,312.0 19,560.0 
6 . . .. 20.0 1,047.0 33,920.0 
7 30.0 1,142.4 17,960.0 
These results are in perfect harmony with those obtained in 
previous years. There are, however, a few spots in which changes 
are taking place, which is rather surprising in consideration of the 
large amount of chlorin present in the surface portions. The amount 
of chlorin falls off rapidly with depth, for the first foot of soil, in¬ 
cluding the surface, carried only 3,870.0 p. p. m. of chlorin. The 
amount of chlorin is by no means constant. Samples of “brown 
spots” on this land, which were taken to see whether we were quite 
correct in our judgment, gave the following results: 
Samples taken July 10, 1912. 
Nitric Nitrogen Total Nitrogen Chlorin 
8 . 779.1 1,319.2 18,743.0 
9 ‘ ’ ’ * * . . 881.0 1,339.6 19,089.0 
THE THIRD PLACE CHOSEN. 
The third place selected was a larger area and was divided into 
equal sections, one-sixth-acre each. The surface-portion was 
sampled to a depth of seven inches, the top three inches was taken 
as one and the succeeding four inches as a second sample. Sixty 
samples were taken to these respective depths from each one-sixth- 
acre, united, thoroughly mixed and cut down to form a composite 
sample. We took, in sampling the whole acre, 720 individual 
samples. In the samples taken on April 15, 1912, only the surface- 
samples, i. e., the top three inches, were taken. This land was fur¬ 
ther sampled by taking vertical sections from the surface down to 
the water-plane. Three such sets of samples were taken during the 
period of observation. On one occasion seven such sections were 
