Oct. 8, 1917 
Nitrate-Nitrogen Accumulation in Soil 
59 
content of this soil varied from about 12 to 25 c. c. per 100 gm. of soil, 
averaging approximately 20 c. c. 
The writers have also endeavored to increase aeration by forcing air 
daily into horizontal perforated tubes placed underneath both cultivated 
and uncultivated plots of ground. Such experiments have been con¬ 
ducted for two seasons without the differences in nitrate accumulation 
exceeding the experimental error. 
Such data as are available, therefore, upon the effect of increasing 
aeration under conditions more nearly approaching normal field condi¬ 
tions are in accord with the laboratory results. 
There is another angle from which the question of availability of 
oxygen in soils of different types, different depths, etc., under natural 
conditions can be approached. One can readily measure, with a fair 
degree of accuracy, the oxygen actually potentially available for bacterial 
metabolism. Such data, together with data as to the quantity of oxygen 
essential for normal aerobic activity, should be very valuable in connec¬ 
tion with the problem under consideration. 
Fortunately Schlcesing (12), in his original classic researches upon 
nitrification, secured very definite data, which, so far as the writers are 
aware, has never been refuted, on the effect of varying the oxygen con¬ 
tent of the atmosphere upon nitrate accumulation. Working with a 
fertile soil, rich in humus—containing 0.263 P er cent of nitrogen and of 
the following mineral composition: Clay (< %rgile ), 14.6 per cent; chalk 
(calcaire firi), 19.5; silicious sand (sable siliceux) } 48; calcareous sand 
(sable calcaire ), 17.7—and with a moisture content of 15.9 parts per 100, 
he secured the results given below: 
Oxygen, per cent. 1.5 6 11 16 21 
Nitric acid formed, mgm. 45. 7 95. 7 132. 5 246. 6 162. 6 
Incubation was for four weeks at temperature of 21 0 to 29 0 C. 
Duplicating this experiment, except that one sample received no 
oxygen, the moisture content was 24 parts per 100 of soil (as much as 
it would absorb), and incubation eight instead of four months, he secured 
the following results: 
Ogygen, per cent. o 6 11 16 21 
Nitric acid formed, mgm.. —64 199 222 203 225 
In this instance, with the capacity of the soil to hold air reduced very 
low and an oxygen content in the air of only 6 per cent, practically as 
much nitric acid was formed as with normal atmospheric oxygen content, 
while with 11 per cent of oxygen the quantity was equal to that of normal 
air. 
It is also interesting to note that the carbon dioxid evolved, a factor, 
as the evidence shows, more or less dependent upon oxygen content, 
was practically as great at 6 per cent of oxygen as with 21 per cent. 
