9 2 The Colorado Experiment Station. 
optimum amount is probably below rather than materially above 
this percentage, ihe determination of the optimum amount of 
moistui e under specific and varied conditions would be interesting 
but is a detail not included in the general features which I am 
endeavoring to present. We have the maximum nitrification in 
the sample containing 20 percent of water at the end of the experi¬ 
ment. My judgment is that this amount had scarcely varied at all 
during the experiment. On the other hand we have the maximum 
fixation in the two samples containing 13.5 and 17.5 percent re¬ 
spectively. 1 hese results may be accidental but they agree well 
with my observations in the field. The amount of fixation, how¬ 
ever, is quite uniform and the addition of water, at least up to 
: 7-5 percent has clearly promoted it. 
The chemical composition of this soil is fairly represented by 
our Laboratory Nos. 724 and 725, representing the soil and sub¬ 
soil from a portion of this same tract. These analyses were given 
in Bulletin 155, p. 36. 
ANALYSES 
Insoluble . 
Silicic acid . 
Sulfuric acid . 
Chlorin . 
Phosphoric acid . 
Carbonic acid . 
Lime . 
Magnesia . 
Sodic oxid . 
Potassic oxid . 
Ferric oxid . 
Aluminic oxid . 
Manganic oxid . 
Ignition . 
Sum . 
Oxygen equiv. to chlorin 
Total . 
Total nitrogen . 
Humus . 
XCII 
XCIII 
Soil 
.Subsoil 
Laboratory 
Laboratory 
No. 724 
No. 725 
Percent 
Percent 
54.653 
57.068 
19.805 
12.754 
0.047 
0.049 
0.032 
0.059 
0.120 
0.127 
3.048 
6.312 
6.100 
8.465 
1.355 
1.448 
0.290 
0.432 
0.872 
0.742 
5.601 
3.499 
3.738 
5.397 
0.118 
0.026 
5.072 
3.887 
100.851 
100.265 
0.007 
0.013 
100.844 
100.252 
0.147 
0.426 
0.069 
While these analyses are not made on the soil actually used 
they serve to represent its composition as well as a sample taken 
in any fair-sized field may represent its soil. 
The amount of nitrogen fixed is very large and seems incred- 
ible. Taking 10.54 milligrams as the quantity fixed in 100 grams 
of soil in twenty-seven days and calculating the amount that would 
be fixed in the top two inches of the soil per acre, we have 937 
pounds, or for an acre-foot 5*622 pounds, equivalent to about 17.5 
tons of proteids (N x 6.25) per acre-foot, a quantity which seems 
extremely large, but this is the result actually obtained. 
