4 6 
Journal of Agricultural Research 
Vd. XI, No. 2 
(e) The shape and size of the container, as well as methods of pre¬ 
venting evaporation and contamination, were without effect except when 
the container was stoppered tightly, and the volume of inclosed air was 
relatively small in proportion to soil volume. 
The principal vital factor which the above variations would seem to 
affect is the access of oxygen. The fact that the factors influencing the 
access of oxygen could be varied as widely as in the experiments just 
recorded without in turn effecting the aerobic processes, suggested the 
advisability of further study along similar lines. The subsequent experi¬ 
ments herein reported were therefore designed to ascertain the effect 
produced upon the accumulation of nitrate nitrogen in soils by varying 
some of the more important factors controlling aeration. 
According to Buckingham (i), aeration is a direct function of porosity 
or free pore space. This being true, the factors influencing porosity are 
the factors influencing aeration. In any given soil porosity is a direct 
function of compactness and moisture content, being in an inverse ratio 
to either one considered alone. In addition to these two variables, it is 
also essential to take into consideration the length of column or depth to 
which air or oxygen must diffuse. Accordingly these were the factors 
varied in the succeeding experiments. Typical experiments of those 
conducted will now be reported. 
EXPERIMENTAL DATA 
The data reported in Table II were secured under the following con¬ 
ditions: All samples contained 50 mgm. of nitrogen as ammonium sul¬ 
phate and 0.5 gm. of calcium carbonate per 100 gm. of soil. Samples were 
incubated in a moist chamber at room temperaure for the periods indi¬ 
cated in the table. Such loss in moisture as occurred was replaced from 
time to time. Samples 1 and 2 were contained in large, open petri 
dishes. Samples 3 and 4 vrere incubated in wide-mouthed 500-c. c. 
bottles plugged with cotton. Samples 5 and 6 were in glass cylinders 
24 inches high and 2% inches in diameter. The moisture content of all 
samples was 20 c. c. per 100 gm. of soil. The samples marked “loose” 
were placed in the containers and the latter gently tapped on the bottom 
to cause the soil to settle into the larger openings. Those marked 
“compact” were so tamped that the same weight of soil occupied only 
two-thirds the volume that the “loose” soil occupied or in other words 
there were times by weight as much soil in same containers. 
From the data contained in Table II the following facts seem evident: 
(1) The “compact” samples in the major portion of possible comparisons 
show a higher nitrate gain than do the “ loose ” samples. The greater gains 
in “loose” samples are so small as to be negligible. (2) The deeper soil 
columns show higher nitrate gains than do the shallow. (Samples 5 and 
6 are exceptions, but for some reason these failed to show active nitrifi¬ 
cation. Other data recorded in this paper show that this low nitrifica- 
