Factors affecting soil formation


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Factors affecting soil formation

  1. 1. Factors Affecting Soil Formation Ag I Northshore High
  2. 2. Soil Formation Terms <ul><li>Topography – the slope of the ground surface as determined by features such as mountains, hills, plains, etc. </li></ul><ul><li>Weathering – the process by which rocks and minerals are changed to soils. </li></ul><ul><li>Soil formation – process by which rocks and minerals are changed to soil over a period of time . </li></ul><ul><li>Rock – solid & massive materials composed of one or more minerals. </li></ul>
  3. 3. Soil Formation Terms <ul><li>Mineral – chemical compound neither animal nor vegetable; results from inorganic processes of nature. </li></ul><ul><li>Loess – silty, floury material laid down by wind (fine soil particles) </li></ul><ul><li>Alluvium – soil material laid down by running water in the flood plains or bottomlands of rivers and streams. </li></ul>
  4. 4. What affects soil formation? <ul><li>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. </li></ul><ul><ul><li>Parent material </li></ul></ul><ul><ul><li>Climate </li></ul></ul><ul><ul><li>Living organisms (biota) </li></ul></ul><ul><ul><li>Topography </li></ul></ul><ul><ul><li>Time </li></ul></ul>
  5. 5. Parent Material <ul><li>Alluvium – finely pulverized rock laid down by running water. Mostly silt and clay particles with some sand. </li></ul><ul><li>Marine Deposits – finely pulverized rock laid down under sea. This material has been thrust up by shifts in the earth’s crust. </li></ul><ul><li>Loess – silty, floury material laid down by winds. Mostly silt and clay with little or no sand. </li></ul>
  6. 6. Climate <ul><li>Physical weathering – results from mechanical agents, such as heating & cooling, freezing & thawing, &/or abrasion. </li></ul><ul><ul><li>Materials are still the same at the molecular level. </li></ul></ul><ul><ul><li>Materials are classified by the way they have been moved or scattered </li></ul></ul>
  7. 7. Climate <ul><li>Chemical weathering – Results from the action of water, oxygen, & carbon dioxide on the rocks. </li></ul><ul><ul><li>Carbon dioxide mixed with rain water forms a weak acid, speeding up the weathering of parent material. </li></ul></ul><ul><ul><li>Materials that have been chemically weathered are no longer the same at the molecular level. </li></ul></ul><ul><ul><ul><li>Example – Clay has been synthesized into something physically and chemically different from the parent rock. </li></ul></ul></ul>
  8. 8. Climate <ul><li>Climate is the single most important factor affecting soil formation. </li></ul>
  9. 9. Biota <ul><li>Biota is made up of living organisms such as plants, animals, insects, bacteria, & fungi. </li></ul><ul><ul><li>Plants have the most important affect because they determine the type & amount of organic matter. </li></ul></ul><ul><ul><li>Animals & insects mix and aerate the soil as well as add organic matter. </li></ul></ul><ul><ul><li>In the US, organic matter in the soils increases as you move north &/or east. Why? </li></ul></ul>
  10. 10. Topography <ul><li>Topography refers to the “lay of the land” or the angle & length of the slope. </li></ul><ul><li>It affects soil formation because it influences runoff, drainage, & erosion. </li></ul><ul><li>It also may affect the type & amount of plant growth (biggest factor in determining type & amount of organic matter) </li></ul>
  11. 11. Topography <ul><li>Steep slopes </li></ul><ul><ul><li>High runoff rates </li></ul></ul><ul><ul><li>Less water infiltration </li></ul></ul><ul><ul><li>Fewer plant forms </li></ul></ul><ul><ul><li>Less organic matter </li></ul></ul><ul><ul><li>Increased erosion </li></ul></ul><ul><ul><li>Thinner surface soil </li></ul></ul><ul><ul><li>Slower formation/development </li></ul></ul>
  12. 12. Topography <ul><li>Level to Gentle slope </li></ul><ul><ul><li>Little runoff </li></ul></ul><ul><ul><li>Increased water infiltration </li></ul></ul><ul><ul><li>Faster plant growth leading to more organic matter </li></ul></ul><ul><ul><li>Less erosion </li></ul></ul><ul><ul><li>Deeper surface soil </li></ul></ul><ul><ul><li>Faster formation/development </li></ul></ul><ul><ul><ul><li>Excessive water can slow development </li></ul></ul></ul>
  13. 13. Time <ul><li>As soon as material has become loose enough to hold enough water, air, and nutrients for plant growth, it is considered a soil. </li></ul><ul><ul><li>Soil formation/development may take place over several centuries or just a few days. </li></ul></ul>
  14. 14. Time <ul><li>Young soils </li></ul><ul><ul><li>Volcanic or alluvial in origin </li></ul></ul><ul><ul><li>Have greater fertility </li></ul></ul><ul><ul><li>Have poorly developed profiles </li></ul></ul><ul><ul><li>Usually they are highly productive. </li></ul></ul><ul><ul><li>Where are the youngest soils in Louisiana located? </li></ul></ul>
  15. 15. Time <ul><li>Old soils </li></ul><ul><ul><li>Have well developed soil profiles </li></ul></ul><ul><ul><li>Have an increased clay content </li></ul></ul><ul><ul><li>More acid pH </li></ul></ul><ul><ul><li>Nutrients are leached </li></ul></ul><ul><ul><li>Lower fertility & productivity than younger soils. </li></ul></ul>
  16. 16. Student Activity <ul><li>For next class period, bring in a soil sample in a ziplock bag. </li></ul><ul><ul><li>On the bag mark your name, where you collected the sample, and what horizon it came from </li></ul></ul><ul><ul><li>I will keep the samples for other activities in this unit. </li></ul></ul><ul><ul><li>10 BONUS POINTS to all who participate! </li></ul></ul>