How is soil formed?
Soil formation reflects the complex interaction of many factors, among the most important of which are:
- Parent material – Few soils weather directly from the underlying rocks. These “residual” soils have the same general chemistry as the original rocks. More commonly, soils form in materials that have moved in from elsewhere. Materials may have moved many miles or only a few feet. The material in which soils form is called “parent material.” In the lower part of the soils, these materials may be relatively unchanged from when they were deposited by moving water, ice, or wind.
- Climate – Soils vary, depending on the climate. Temperature and moisture amounts cause different patterns of weathering and leaching. Wind redistributes sand and other particles especially in arid regions. The amount, intensity, timing, and kind of precipitation influence soil formation. Seasonal and daily changes in temperature affect moisture effectiveness, biological activity, rates of chemical reactions, and kinds of vegetation.
- Topography – Slope and aspect affect the moisture and temperature of soil. Steep slopes facing the sun are warmer, just like the south-facing side of a house. Steep soils may be eroded and lose their topsoil as they form. Thus, they may be thinner than the more nearly level soils that receive deposits from areas upslope. Deeper, darker colored soils may be expected on the bottom land.
- Biological factors – Plants, animals, micro-organisms, and humans affect soil formation. Animals and micro-organisms mix soils and form burrows and pores. Plant roots open channels in the soils. Different types of roots have different effects on soils. Grass roots are “fibrous” near the soil surface and easily decompose, adding organic matter. Taproots open pathways through dense layers. Micro-organisms affect chemical exchanges between roots and soil. Humans can mix the soil so extensively that the soil material is again considered parent material.
- Time – Time for all these factors to interact with the soil is also a factor. Over time, soils exhibit features that reflect the other forming factors. Soil formation processes are continuous. Recently deposited material, such as the deposition from a flood, exhibits no features from soil development activities. The previous soil surface and underlying horizons become buried. The time clock resets for these soils. Terraces above the active floodplain, while genetically similar to the floodplain, are older land surfaces and exhibit more development features.
How are soils classified?
Soils are named and classified on the basis of physical and chemical properties in their horizons (layers). “Soil Taxonomy” uses color, texture, structure, and other properties of the surface two meters deep to key the soil into a classification system to help people use soil information. (Source: NRCS)
Soil texture is determined by the composition of the soil particles. There are three categories for soil particles – sand, silt and clay. The following textural triangle represents all possible combinations of soil particles:
Explore soil types classified by soil texture in the map below.
What is soil disturbance?
Soil disturbance is the movement or alteration of soil. Generally, soil disturbance can occur in three different forms (NRCS):
- Physical disturbance – ex. compaction, grading, filling, soil excavating or topsoil stripping
- Biological disturbance – ex. overgrazing,which limits the plants ability to harvest CO2 and sunlight
- Chemical disturbance – ex. over application of nutrient and pesticide, can disrupt the soil food web functions
What impact does soil disturbance have?
Almost all types of disturbance degrade soil structure. One of the most serious problems is compaction caused by vehicles, tire dynamics, equipment operations, pedestrians, animals and bicycles. Grading and filling are the most destructive, but even minimal activity can have significant adverse effects on soil structure. Loamy soils are more sensitive to compaction than sandy soil, and wet soils are much more vulnerable than dry soils. (D., Bainbridge)
Mining is another source of physical soil disturbance. Utah has a rich history in mining metals that has been integral to the development of the state since the 1860s. Park City and Alta, were home to early mining communities.
Explore mining activities in the Central Wasatch in the map below.