62 
Journal of Agricultural Research 
Vol. XI, No. 2 
With these facts in mind are quoted the following figures from Leather’s 
paper. These data were secured from experiments with an unmanured 
fallow soil and show the variations in analysis for a number of dates. 
Depth. 
ist 12 inches. 
2d 12 inches. 
3d 12 inches. 
4th 12 inches, 
5th 12 inches 
6th 12 inches 
7th 12 inches, 
Per cent oxygen. 
Per cent COa. 
Per cent gas in 
volume. 
12. 7 to 18. 6 
2. 9 tO 12 
18. 6 to 41. 2 
9. 2 to 18. 5 
3. 9 to 8.5 
14. 8 to 39. O 
9. 7 to 17. 7 
i. 9 to 6. 9 
23. 8 to 42. 2 
7. 6 to 17. 8 
1. 4 to 7. 0 
21. 2 tO 45. 3 
11. 9 to 14. 9 
2. 7 to 8. 5 
3. 8 to 28. 2 
12. 7 (one anal¬ 
ysis). 
6.1 (one analy¬ 
sis). 
22. 6 to 25. 3 
15. 5 (one anal¬ 
ysis). 
8.2 (one analy¬ 
sis). 
The low oxygen figures followed the heavy monsoon rains, while the 
high figures followed prolonged droughts. 
As a general summary of the above-reported soil atmospheric analysis, 
coming from as wide a variety of localities, conditions, etc., as they do, 
one may say: 
(a) The percentage of air by volume in soil rarely ever falls below 20 
even several feet below the surface where soil has never been artifically 
disturbed. Excessive rains or excessive trampling of cattle when the 
soil is moist may reduce the percentage. 
(1 b ) The percentage of oxygen contained in the free soil atmosphere is 
normally only slightly below that in the atmospheric air. This is true to 
such depths as one should expect appreciable nitrification to take place. 
The exceptional conditions just cited, together with heavy applications 
of green or stable manure, as well as the presence of certain growing 
plants, may cause a marked reduction in the oxygen content. Such 
exceptional reductions rarely ever cause a reduction of more than one-half 
the atmospheric content, even several feet below the surface. 
(c) The carbon-dioxid content of the soil air is usually materially 
higher than that of the atmospheric air. Any factor tending to increase 
the bacterial activity or to decrease the exchange of gases tends to 
increase the carbon-dioxid content at the expense of oxygen. The 
proportion of carbon dioxid present in free soil air rarely ever exceeds 
2 per cent, and usually is only a few tenths of 1 per cent. Owing to 
the greater solubility of carbon dioxid, the dissolved soil atmosphere is 
usually high in this constituent. According to Leather, the major por¬ 
tion of this is probably in loose chemical combination as an acid 
carbonate. 
Since the composition of the soil atmosphere is directly controlled 
by the rate of exchange of gases between it and the atmospheric air, it 
is evident from slight variations in composition reported above that 
