The typically developed soil horizons, as illustrated in Figure 5. E— the eluviated leached layer from which some of the clay and iron have been removed to create a pale layer that may be sandier than the other layers. Although rare in Canada, another type of layer that develops in hot arid regions is known as caliche pronounced ca-lee-chee.
It forms from the downward or in some cases upward movement of calcium ions, and the precipitation of calcite within the soil.
When well developed, caliche cements the surrounding material together to form a layer that has the consistency of concrete. Like all geological materials, soil is subject to erosion, although under natural conditions on gentle slopes, the rate of soil formation either balances or exceeds the rate of erosion.
Human practices related to forestry and agriculture have significantly upset this balance. Soils are held in place by vegetation. When vegetation is removed, either through cutting trees or routinely harvesting crops and tilling the soil, that protection is either temporarily or permanently lost. The primary agents of the erosion of unprotected soil are water and wind. Water erosion is accentuated on sloped surfaces because fast-flowing water obviously has greater eroding power than still water Figure 5.
Raindrops can disaggregate exposed soil particles, putting the finer material e. Sheetwash , unchannelled flow across a surface carries suspended material away, and channels erode right through the soil layer, removing both fine and coarse material.
The materials increase stream load to cause floods. Erosion leaves the land bare and unproductive. Running Water,. Wind, and. Glacier Ice. Over cultivation by farmers,. Overgrazing by herds of cattle, sheep etc,. Deforestation by local groups. Irrigation by farmers. Contour ploughing along sloping grounds. Strip Cropping across slopes. Terracing along slopes. Damming of Gullies.
Removing cropland from production to allow soil. Creating windbreaks to reduce wind speed and erosion. Review Questions:. Answer the following questions and submit your answers in class. Consult your textbook for help. List the three main classes of rocks and explain how each of the three categories of rocks differs from each other.
Nitrogen is the most common element in the atmosphere, but it exists in a form most life forms are unable to use.
Special bacteria found only in soil provide most nitrogen compounds that are usable, bioavailable, by life forms. These nitrogen-fixing bacteria absorb nitrogen from the atmosphere and convert it into nitrogen compounds.
These compounds are absorbed by plants and used to make DNA, amino acids, and enzymes. Animals obtain bioavailable nitrogen by eating plants, and this is the source of most of the nitrogen used by life. That nitrogen is an essential component of proteins and DNA. Soils range from poor to rich, depending on the amount of humus they contain.
Soil productivity is determined by water and nutrient content. Freshly created volcanic soils, called andisols , and clay-rich soils that hold nutrients and water are examples of productive soils. Water erosion is accentuated on sloped surfaces because fast-flowing water has higher eroding power than still water. Raindrops can disaggregate exposed soil particles, putting the finer material e. Sheetwash , unchannelled flow across a surface carries suspended material away, and channels erode right through the soil layer, removing both fine and coarse material.
Wind erosion is exacerbated by the removal of trees that act as windbreaks and by agricultural practices that leave bare soil exposed. Tillage is also a factor in soil erosion, especially on slopes, because each time a cultivator lifts the soil, it is moved a few centimeters down the slope. Earth has two important carbon cycles.
One is the biological one, wherein living organisms, mostly plants, consume carbon dioxide from the atmosphere to make their tissues, and then, after they die, that carbon is released back into the atmosphere when they decay over years or decades.
A small proportion of this biological-cycle carbon becomes buried in sedimentary rocks: during the slow formation of coal, as tiny fragments and molecules in organic-rich shale, and as the shells and other parts of marine organisms in limestone. The geological carbon cycle below shows the various steps in the process not necessarily in this order :. Under these conditions, the climate remains relatively stable. Privacy Policy. Skip to main content.
Module 4: Weathering and Soil Formation. Search for:. Why It Matters: Weathering and Soil Formation Explain the formation of soils, different weathering processes and erosion. Introduction When most people think about the resources we use, most of them will immediately think about water and air and fossil fuels.
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