140 
Journal o) Agricultural Research 
Vol. XXV, No. 3 
to a depth of 16 cm., without otherwise altering the soil, changed the 
oxygen supplying power from 0.0119 to 0.0096 cc. per hour for this 
cylinder. Wetting the soil diminished this value from 0.0096 to 0.005 5 
cc. per hour, and packing the wet soil diminished it from 0.0055 to 
0.0002 cc. per hour. 
The numerical results just given in terms of the lengths of the color- 
change periods and in terms of cubic centimeters per hour for the cylinder 
used, have been approximately calculated also to terms of cubic centi¬ 
meters per hour per square meter, cubic millimeters per hour per square 
meter, and milligrams per hour per square meter. They are shown in 
all five different ways in Table II. Of course it is understood that these 
values are all very rough approximations, and they are rounded off to 
convenient decimals. The calculations have been made by assuming a 
temperature of 20° C. and a barometric pressure of 76 cm. of mercury. 
The different lines of the tabulation represent merely different ways of 
expressing the four different values dealt with. 
Table II .—Approximate results of oxygen tests on moist and wet soil 
Moist, loose soil. 
Wet soil. 
1 
Packed, 
wet soil 
Depth (in soil) of absorbing cylinder (cm.).. 
Color-change period in minutes. 
8 
76. 0 
0. 0119 
16 
94. 0 
0. 0096 
1. 0 
13-5 
164. 0 
0. 0055 
0. SO 
II 
505°. 0 
0. 0002 
0. 02 
Cc. per hour cylinder. 
Cc. per hour square meter. 
I. 3 
Cu. mm. per hour per square meter. 
1300. 0 
*• 73 
1000. 0 
• oy 
590.0 
0. 79 
20. 0 
0. 03 
Mgm. per hour per square meter. 
33 
The results of this preliminary study indicate, as was to be expected, 
that the oxygen-supplying power of the soil for a plant root becomes 
less (1) as the root lies deeper in the soil, (2) as the moisture content of 
the soil above the root increases, and (3) as the soil above the root be¬ 
comes more firmly packed. It may perhaps be estimated that the 
oxygen-supplying power of the soil about the roots of ordinary agricuh 
tural plants may be something like 1 per cent as great when the soil i* 
packed and saturated by heavy rains as it is when the soil has recently 
been tilled and is not excessively moist. 
CONCLUSION 
As stated in the introduction, the aim of this preliminary study was 
to test certain suggested and seemingly promising methods of approach 
toward the measurement of the oxygen-supplying power of the soil at 
different depths and under different conditions of soil moisture and of 
packing. The writers believe that this aim has been attained and that 
the method described in the foregoing pages may be regarded as at least 
fairly promising for this kind of measurement. Doubtless many improve¬ 
ments will be made and other methods may be devised, based on the 
same or different principles and procedures. This paper is to be re¬ 
garded merely as a report of progress—enough, however, to show very 
clearly that the dynamic soil feature here considered will not prove to 
be unusually difficult of measurement whenever ecology, agriculture, and 
forestry shall have advanced far enough to require quantitative infor¬ 
mation on the dynamic aspect of soil aeration. 
