The Atmosphere of the Soil: Its Composition and the Causes of Variation

Abstract

1. The free air in the pores of the soil to a depth of 6 inches is very similar in composition to the atmospheric air but it differs in two respects: (a) It contains more CO 2 and correspondingly less oxygen, the average in 100 volumes being 0–25 volume CO 2 and 20–6 of oxygen against 0–03 volume CO 2 . and 20–96 oxygen in atmospheric air. (b) It shows greater fluctuations in composition. Usually the sum of the CO 2 and oxygen is only slightly less than in atmospheric air but at periods when nitrates rapidly increase there is a perceptible falling off of oxygen, and a still greater one in waterlogged soils.