What Are the Main Stages (Addition, Loss, Transformation, Transfer) in Soil Formation?

Soil formation, or pedogenesis, is a continuous process driven by four fundamental sets of events. These are often called the four processes of soil formation:

1. Additions: These are inputs of materials to the soil profile from an external source.
   • Organic Matter: Dead leaves, branches, roots, and organisms decompose on the surface and within the soil, adding humus.
   • Water: Precipitation (rain, snow) adds water, which is the primary medium for all soil processes.
   • Sediment: Wind (aeolian deposits) or water (alluvial deposits) can deposit new mineral particles on the soil surface.
   • Energy: Solar energy (sunlight) heats the soil, driving chemical reactions.
2. Losses: These are the removal of materials from the soil profile.
   • Leaching: Water moving down through the soil dissolves and carries away soluble minerals (like calcium) and nutrients, moving them deep into the profile or out into the groundwater.
   • Erosion: Wind and water carry away the valuable topsoil from the surface.
   • Evaporation & Transpiration: Water is lost from the soil surface and through plants as water vapor.
   • Nutrient Uptake: Plants absorb nutrients from the soil for growth, removing them from the system when harvested.
3. Transformations: These are chemical and physical changes of materials *within* the soil.
   • Decomposition: Microorganisms (bacteria, fungi) break down complex organic matter into simple, stable humus.
   • Weathering: Primary minerals (like feldspar) are chemically altered into secondary minerals (like clay).
   • Aggregation: Soil particles (sand, silt, clay, humus) clump together to form "peds" or soil structure.
4. Transfers (or Translocations): This is the movement of materials from one part of the soil profile to another (up or down).
   • Eluviation: The process of *exit*. Water washes fine clay, iron, and organic matter *out* of an upper horizon (like the A or E horizon).
   • Illuviation: The process of *accumulation*. The materials washed out from above are deposited *into* a lower horizon (like the B horizon).
   • Bioturbation: Earthworms, ants, and burrowing animals move soil particles and organic matter up and down, mixing the horizons.