Soil formation: processes
Simonson (1958) proposed that soil formation could be regarded as two major steps:
- The accumulation of the parent material
- The differentiation of the horizons within the soil profile by soil-forming processes, which can be categorized as:
- Additions
- Removals
- Transfers or translocations of materials
- Transformations
All processes are active to some degree in all soils. The balance between the combination of processes determines the ultimate nature of the soil profile.
Some of the major processes of soil formation within a pedon are summarized in the following table (Adapted from Buol et al., 1980. Soil Genesis and Classification. The Iowa State University Press, Ames).
| Process | Category | Brief Description |
|---|---|---|
| Eluviation | Transfer | Movement of material out of a horizon |
| Illuviation | Transfer | Movement of material out of a horizon |
| Decalcification | Transfer | Reactions that remove CaCO3 from a horizon |
| Calcification | Transfer | Processes leading to accumulation of CaCO3 |
| Desalinization | Transfer | Removal of soluble salts in a horizon |
| Salinization | Transfer | Accumulation of soluble salts in a horizon |
| Solonization | Transfer | Accumulation of sodium salts in a horizon |
| Solodization | Transfer | Leaching of sodium salts from a horizon |
| Leaching | Transfer | Removal of soluble material from the soil |
| Lessivage | Transfer | Physical transfer of clay within the solum |
| Pedoturbation | Transfer | Physical churning and mixing of soil material |
| Podzolization | Transfer | Chemical migration of iron, aluminum, and SOM within the solum |
| Gleization | Transfer | Reduction of Fe3+ to Fe2+ under anaerobic conditions and transfer of Fe2+ |
| Desilication | Transfer | Chemical migration of silica out of the solum leaving iron and aluminum minerals behind |
| Melanization | Transfer | Darkening of A horizon material by addition and mixing of SOM |
| Decomposition | Transfer | Breakdown and loss of minerals and SOM |
| Mineralization | Transfer | Release of inorganic material through decomposition of organic matter |
| Paludization | Transfer | Accumulation of organic materials under anaerobic conditions (Organic soils) |
