a1 (Rothamsted Experimental Station.)
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 CO2 and correspondingly less oxygen, the average in 100 volumes being 0–25 volume CO2 and 20–6 of oxygen against 0–03 volume CO2. and 20–96 oxygen in atmospheric air.
(b) It shows greater fluctuations in composition.
Usually the sum of the CO2 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.
(Received November 20 1914)