4.2 - Soil Forming Processes

Four Soil Forming Processes

  • Additions: Materials added to the soil, such as decomposing vegetation and organisms (organic matter--OM), or new mineral materials deposited by wind or water.
  • Losses: Through the movement of wind or water, or uptake by plants, soil particles (sand, silt, clay, and OM) or chemical compounds can be eroded, leached, or harvested from the soil, altering the chemical and physical makeup of the soil.
  • Transformations: The chemical weathering of sand and formation of clay minerals, transformation of coarse OM into decay resistant organic compounds (humus).
  • Translocations: Movement of soil constituents (organic or mineral) within the profile and/or between horizons. Over time, this process is one of the more visibly noticeable as alterations in color, texture, and structure become apparent.



In an acidic, coarse-textured soil, in a location with a high rainfall, organic matter moves from the litter layer and is deposited on sand grains about 30 centimeters below the soil surface. This is an example of: ‏

Looks Good! Correct: The organic matter moves from the top of the soil to a lower layer. This is an example of translocation.

Calcium carbonate (CaCO3) in a soil layer dissolves in water that is percolating through the soil.  The water flows deeper into groundwater and eventually enters a stream.  This is an example of:

Looks Good! Correct: The calcium carbonate has been removed from the soil profile, so it is an example of loss

A cloud of dust moves into the atmosphere from the Gobi Desert in Asia. The dust, which contains some trace elements, is deposited on the surface of a soil in the Pacific Northwest United States. This is an example of:

Looks Good! Correct: The minerals and elements in dust that are deposited on soils become a new component of that soil. In this regard, this is an addition to the soil.

With respect to the Gobi Desert dust, it was eroded from an Asian soil by the wind.  What process is the erosion an example of? 

Looks Good! Correct: Erosion of any type, water or wind, will remove soil from an area and is considered a loss.

Over the last few years, the farmer has been noticing a decline in productivity.  What process has the corn been exerting on the soil that could cause a loss in productivity? ‏

Looks Good! Correct: One very plausible explanation, given the scenario, is that the corn the farmer has been harvesting has been taking nutrients, such as nitrogen, phosphorus, and potassium, out of the soil. This depletion of the soil's natural fertility by plant harvest is a loss process. The addition of fertilizers is a method for counteracting the loss of fertility.

Volcanic ash, which is largely made up of volcanic glass, has been weathering on the slopes of Mount Hood, Oregon, USA, for thousands of years. The glass is starting to weather into the clay minerals allophane and imogolite. This is an example of: ‏

Looks Good! Correct: Weathering of mineral and conversion from one type (glass) to another (clay) is an example of transformation. For volcanic ash, this weathering process is required before a soil can be considered an Andisol, a soil developed in volcanic materials.