86 The Colorado Experiment Station. 
not determined. Judging from results in other samples, the nitro¬ 
gen was probably almost wholly present as nitric nitrogen. In a 
series of 54 soil samples taken to a depth of six inches the minimum 
of nitric nitrogen equalled 1.5 percent while the maximum, de¬ 
barring an exceptionally high one, was 17.1 percent of the total 
nitrogen. I have already cited an instance in which the nitric 
nitrogen in the third foot of soil was equal to 55.3 percent of the 
total nitrogen, this, however, was an exceptional sample, not in 
the amount of nitric nitrogen present but in the location of the 
nitric acid in the soil. 
The nitric nitrogen in other, mostly surface samples, ranges 
from 16 to 93 percent of the total nitrogen. The latter percentage, 
93, seems extremely high but the total nitrogen was determined 
in duplicate and the determination of the nitric nitrogen was also 
made in duplicate by different parties, using slightly different 
methods of preparing the material for the determination of the 
nitric acid. The agreegent between these determinations was en- 
tirel ysatisfactory. The difference falling in the third decimal place. 
Two samples, our No. 1054 and 1055, illustrate the great variation 
in the amount of nitric nitrogen in affected and unaffected soils. 
No. 1054 is a sample of surface soil taken to a depth of four 
inches near to a recently killed tree, while No. 1055 is also a 
sample of surface soil taken from supposedly unaffected ground 
600 to 800 feet north of the former and just outside of the or¬ 
chard. No. 1054 contained 0.0932 percent total nitrogen and 
0.0150 percent nitric nitrogen, or 16.09 percent of the total; No. 
1055 contained 0.0844 percent total and 0.0003 percent nitric ni- 
tiogen or 0.355 percent of the total. The soil conditions were 
entirely different in these two cases though they were relatively 
close together. 
Fixation —In Bulletin 155 I presented the fact, ascertained 
by Professor Sackett, that the aqueous infusion of some of our 
soils induced a very marked fixation of nitrogen, the maximum 
given at that time being 13.02930 milligrams in 20 days for each 
100 c. c. of mannite solution. The questions pertaining to the 
relation of the azotobacter to fixation and nitrification may be 
worked out in detail by Professor Sackett, but I have endeavored 
to determine the practical facts on a large enough scale to be con¬ 
clusive so far as these processes in our soil are concerned. For 
this purpose I took five portions of soil of 1,250 grams each. The 
moisture content was determined at ioo° and boiled, distilled 
water added to make the total water equal to eighteen percent of 
the moist soil. The weight of the dish and soil was determined 
and noted in order to be able from time to time to add water 
enough to replace loss due to evaporation. At the same time 
