Respiratory Quotient arising from Microbial Activity in Relation to Matric Suction and Air Filled Pore Space of Soil

Abstract

THE moisture content of soil affects the oxygen supply of micro-organisms, and their metabolic activity¹. Oxygen has low diffusibility in water, and at zero matric suction (saturation) oxygen concentration falls rapidly to zero², causing anaerobic conditions to prevail. As matric suction increases, there is increasing occupation of soil pores by air, so the supply of oxygen improves. Thus, by progressively increasing matric suction from zero, a stage will be reached when the proportional occupation of soil pores by air and water corresponds to a transition from anaerobic to aerobic conditions. The extent of the anaerobic interval, in relation to matric suction, will depend on the physical characteristic of the soil. Coarse textured soils usually have a high proportion of large pores that drain at low matric suctions and can be expected to have a short anaerobic interval, while fine textured soils tend to have many small pores that drain at higher matric suctions and can be expected to have a longer anaerobic interval.