6 - Soil phases: the gaseous phase

Summary

Soil acts as a global source, sink and reservoir of gaseous substances contributing to the control of the composition of the atmosphere and affecting the climate conditions of the planet. Despite the importance of the soil gas phase, the study of the processes of production, consumption, and transport of gases in soils still suffers from many uncertainties, particularly methods of measurement. Most frequently, soil gases are monitored as fluxes, or net gas flows at the surface, from which the soil capacity to adsorb or release some gaseous substances is assessed. Surface flux measurements ignore the processes that operate in the soil, and thus many questions remain regarding the mechanisms controlling the fluxes. Another shortcoming is that often the gaseous phase of soil is studied separately from the liquid and solid phases, resulting in serious errors in quantitative evaluation of the soil's capacity to produce, absorb, release and accumulate gaseous substances. The problem concerning the mechanisms and forms of gas transport in such a complicated porous medium also remains open and this restrains the modelling of the gaseous phase dynamics, its vertical and lateral distribution in different types of soils. The spatial and temporal irregularities in gas dynamics require changes to the standard approach of the field studies being carried out only in warm vegetated seasons. Some of these problems will be discussed in this chapter as related to quantitative analyses of the gaseous phase composition and its state in the soil.