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CP Sci 9- 1st Sem.

Gen Chem - 1st Sem.



    1.    Explain how soil forms.

    2.    Describe soil composition and the factors that affect it.

    3.    Describe ways in which humans threaten soil fertility.

    4.    Summarize soil conservation methods that reduce soil errosion.



Soil is a valuable resource that is necessary a necessary ingredient for the feeding of the world.  As populations continue to grow it becomes increasingly important to conserve and maximize the planting areas that remain.


Soil forms from weathered rock and decaying organic material (humus).  The weathered rock contains three noticeable parts: sand, clay and silt.  The amount of each affects the soil's porosity (ability to hold water and air).  Factors that affect soil formation include:

bulletplant and animal material - contributes to the humus
bulleterosion - soils of steep slopes erode before the soil matures
bulletclimate - water, temp., wind, drought, and flooding are all examples of climatic influence 

Soil is classified in two different ways depending on the where the parent material (material from which it was formed) comes from.

bulletresidual soil - made from the bedrock beneath the soil
bullettransported soil - soil whose parent material is not the bedrock that supports it.  Agents of transport include:

The cross section of Earth from the surface to the bedrock is known as the soil profile.  Within the soil profile there are three distinct horizons.

bulletsoil horizon-A
bulletdarkest layer
bulletcontains the largest amount of humus (~50% is optimal)
bulletsoil horizon-B
bulletbrown to slightly reddish in color
bulletcontains clay, oxidized metals (rust) and dissolved minerals
bulletsoil horizon-C
bulletcontains slightly weathered bedrock (parent) material
bulletparent (unweathered) material


(www.trentu.ca/ers/images/ soil_profile_diag.jpg)


Soil Conservation

Just like water and the oxygen we breath, soil is a necessary component in sustaining life on this planet.  Soil supports plant growth which supports animal populations which ultimately support the human race (top of the food chain).  When talking about soil conservation it is important to know that although the world is covered with rocky surfaces, there is less than 25% of that land that is suitable for growing crops.

The ability of soil to support plant growth is called fertility.  Soil fertility is determined by the amounts of water, dissolved minerals and humus that is available to support plant growth.  Fertility can be reduced by the following conditions:

bulletsoil depletion (over farming) - as plants grow they remove minerals from the soil.  As the plant materials are harvested the minerals are harvested along with them.  Possible solutions include the following:
bulletcrop rotation - not all plants require the same nutrients.  As plants are plowed under after harvest, nutrients are returned to the soil.
bulletnot planting for long periods of time - not often practiced as farmers depend on their yields to survive
bulletfertilization - effective for the crop but the runoff of excess minerals often poisons the water supply

Demonstration of a 4 bed crop rotation system   (www.netspace.net.au/~atkinson/ images/croprotate.gif)

bulletsalinization (mineral buildup) - occurs in irrigated desert areas.  Minerals are concentrated in high levels after evaporation leaving the ground in a toxic state.

            (www.grida.no/caspian/ image/desert.jpg)

bulleterosion by wind and water - it is estimated that we are losing soil 17 times faster than it was created.  Some methods of controlling it are:
bulletplanting windbreaks (shelterbelts) - tall trees and high brush are planted to buffer the oncoming wind 
bulletcontour farming - inhibits water from rapidly eroding the topsoil.  Common in irrigation dependent regions.

(www.fertile-minds.org/common/ images/photos/soil.jpg)
bulletterracing - slows the rate of water runoff up to 50%

    Terrace Farming(www.redbrick.dcu.ie/.../ perTerraceFarming.jpg)
bulletstrip-cropping - planting in alternating bands of vegitation.

    Strip cropping corn in Dubuque County, IA.(www.usda.gov/oc/ photo/b94c3938.jpg)
bulletno-till farming - turning the soil once per harvest cycle.  Allows the soil to become firm which

        reduces the amount of wind and water erosion.

(www.erca.org/soil/ cfarming/tractor.jpg)






Last modified: September 05, 2004