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Factors Affecting Soil Formation

Factors Affecting Soil Formation. Ag I Northshore High. Soil Formation Terms. Topography – the slope of the ground surface as determined by features such as mountains, hills, plains, etc. Weathering – the process by which rocks and minerals are changed to soils.

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Factors Affecting Soil Formation

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  1. Factors Affecting Soil Formation Ag I Northshore High

  2. Soil Formation Terms • Topography – the slope of the ground surface as determined by features such as mountains, hills, plains, etc. • Weathering – the process by which rocks and minerals are changed to soils. • Soil formation – process by which rocks and minerals are changed to soil over a period of time. • Rock – solid & massive materials composed of one or more minerals.

  3. Soil Formation Terms • Mineral – chemical compound neither animal nor vegetable; results from inorganic processes of nature. • Loess – silty, floury material laid down by wind (fine soil particles) • Alluvium – soil material laid down by running water in the flood plains or bottomlands of rivers and streams.

  4. What affects soil formation? • Soil characteristics develop as a result of their origin and environment. Soil begins as a particular rock material and develops slowly over many years. Each soil is a product of a combination of the following factors. • Parent material • Climate • Living organisms (biota) • Topography • Time

  5. Parent Material • Alluvium – finely pulverized rock laid down by running water. Mostly silt and clay particles with some sand. • Marine Deposits – finely pulverized rock laid down under sea. This material has been thrust up by shifts in the earth’s crust. • Loess – silty, floury material laid down by winds. Mostly silt and clay with little or no sand.

  6. Climate • Physical weathering – results from mechanical agents, such as heating & cooling, freezing & thawing, &/or abrasion. • Materials are still the same at the molecular level. • Materials are classified by the way they have been moved or scattered

  7. Climate • Chemical weathering – Results from the action of water, oxygen, & carbon dioxide on the rocks. • Carbon dioxide mixed with rain water forms a weak acid, speeding up the weathering of parent material. • Materials that have been chemically weathered are no longer the same at the molecular level. • Example – Clay has been synthesized into something physically and chemically different from the parent rock.

  8. Climate • Climate is the singlemost important factor affecting soil formation.

  9. Biota • Biota is made up of living organisms such as plants, animals, insects, bacteria, & fungi. • Plants have the most important affect because they determine the type & amount of organic matter. • Animals & insects mix and aerate the soil as well as add organic matter. • In the US, organic matter in the soils increases as you move north &/or east. Why?

  10. Topography • Topography refers to the “lay of the land” or the angle & length of the slope. • It affects soil formation because it influences runoff, drainage, & erosion. • It also may affect the type & amount of plant growth (biggest factor in determining type & amount of organic matter)

  11. Topography • Steep slopes • High runoff rates • Less water infiltration • Fewer plant forms • Less organic matter • Increased erosion • Thinner surface soil • Slower formation/development

  12. Topography • Level to Gentle slope • Little runoff • Increased water infiltration • Faster plant growth leading to more organic matter • Less erosion • Deeper surface soil • Faster formation/development • Excessive water can slow development

  13. Time • As soon as material has become loose enough to hold enough water, air, and nutrients for plant growth, it is considered a soil. • Soil formation/development may take place over several centuries or just a few days.

  14. Time • Young soils • Volcanic or alluvial in origin • Have greater fertility • Have poorly developed profiles • Usually they are highly productive. • Where are the youngest soils in Louisiana located?

  15. Time • Old soils • Have well developed soil profiles • Have an increased clay content • More acid pH • Nutrients are leached • Lower fertility & productivity than younger soils.

  16. Student Activity • For next class period, bring in a soil sample in a ziplock bag. • On the bag mark your name, where you collected the sample, and what horizon it came from • I will keep the samples for other activities in this unit. • 10 BONUS POINTS to all who participate!

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