Soil Chemistry and Processes

Soil Phases and Chemical Processes

• Soils have the ability to bind chemical elements, preventing them from being leached into groundwater or transported laterally through subsoil, which would lead to pollution problems.
• Before the mid-1800s, soil was considered a passive support medium for plants, but J.T. Way's studies in the 1850s demonstrated the reactivity of the soil solid phase.
• Chemical substances in soils can be retarded by the solid phase, and their mobility is dictated by processes that distribute them between the immobile soil solids and mobile soil water and gaseous phases.

Soil Phases

• The soil environment consists of three phases: soil atmosphere (gaseous phase), soil solution (aqueous phase), and soil solids (solid phase).
• The soil solid phase is a composite of several phases, including:
  • Mineral (inorganic compounds)
  • Humus (soil organic matter)
  • Biotic (living organisms)
• Boundary phases exist between soil minerals or organic matter and the soil solution, and include:
  • Soil exchanger phase (exchangeable ions)
  • Adsorbed phase (ions and molecules retained by processes other than exchange or precipitation)

Soil Environment Boundaries

• The soil environment is bounded by the soil surface and soil parent material, with arbitrary lateral boundaries that can be imposed.
• Soils are open systems, allowing energy and matter to enter and exit at these boundaries.