Soil Atmosphere as Influenced by Temperature and Moisture

Abstract Composition of the atmosphere of Yolo sandy loam soil columns was determined at different depths and different soil moisture conditions. After saturation with water, soil columns were placed in 30, 25, 20, 15, or 10C constant temperature rooms and moisture was allowed to evaporate from the soil surface. Soil moisture content was determined with a gamma‐ray densitometer; CO 2 , O 2 , and N 2 concentrations were determined by gas chromatography. After 14 days at 30C, moisture tension at the 65 cm depth was 0.1 bar and the soil atmosphere contained 17% CO 2 and 4% O 2 . At the 35‐cm depth, the moisture was 0.3 bar and the CO 2 and O 2 concentrations were 7% and 14%, respectively. At the 5‐cm depth the CO 2 did not rise over 1.5%. At lower temperatures the CO 2 did not rise over 1.5%. At lower temperatures the CO 2 concentrations were less and the maximum was reached more slowly. However, the N 2 concentration increased to almost 90%. At each temperature and all depths, rapid changes occurred in the concentration of gases when the soil moisture tension reached 0.10 to 0.15 bar.