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Soil Science

Soil Science. Soil. Is made of Inorganic minerals Organic matter Air (pore space) water. Soil Properties. Fig. 10.17, p. 224. Water. Water. 100%clay. High permeability. Low permeability. 0. Increasing percentage clay. 80. 20. Increasing percentage silt. 60. 40. 40. 60. 20.

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Soil Science

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  1. Soil Science

  2. Soil • Is made of • Inorganic minerals • Organic matter • Air (pore space) • water

  3. Soil Properties Fig. 10.17, p. 224 Water Water 100%clay High permeability Low permeability 0 Increasing percentage clay 80 20 Increasing percentage silt 60 40 40 60 20 80 0 80 60 40 20 100%sand 100%silt Increasing percentage sand • Infiltration • Leaching • Porosity/permeability • Texture • Structure • pH Fig. 10.16, p. 224

  4. Characteristics of Soil • Bulk density/Porosity • Permeability/Infiltration • Texture • Soil Moisture • Cation Exchange Capacity • pH • Fertility

  5. Bulk Density • Measures how tightly packed the soil is • Measured as dry weight/volume (g/cm3) • Determined by both particle size and shape

  6. Soil Color Munsell Notation Hue Value Chroma

  7. Munsell Notation Value (amount of black or white added to the color Hue (position on the color wheel) Chroma (amount of brightness of saturation of the color

  8. Soils can vary greatly in color depending on the soil forming factors and other conditions. The soil lets water move through easily and tends to be well drained and high in oxygen (oxygen) The soil lets water move through slowly and tends to be wet and low in oxygen (reduced)

  9. Soil Structure (With Structure) Granular Blocky Columnar Prismatic Platy

  10. Soil Consistence Squeeze a moist soil ped to see if it is: Loose* You have trouble picking out a single ped and the structure falls apart before you handle it.* Friable The ped breaks with a small amount of pressure * Soils with “single grained” structure always have loose consistence. Firm The ped breaks when you apply a good amount of pressure and dents your fingers before it breaks. Extremely Firm The ped can’t be crushed with your fingers (you need a hammer!).

  11. Permeability/Infiltration • The rate at which water moves through the soil • Measured as distance/time (mm/hr or inches/min) • Determines how much run off will occur during a rain event

  12. Texture • Distribution of different size particles within a soil • Three particle sizes are defined by the USDA • Sand (largest) • Silt (intermediate) • Clay (smallest) • The percentage of each determines the soil type

  13. Soil Texture

  14. Soil Texture • The way a soil “feels” is called the soil texture. • Soil texture depends on the amount of each size of particle in the soil. • Sandare the largest particles and they feel “gritty.” • Siltare medium sized, and they feel soft, silky or “floury.” • Clayare the smallest sized particles, and they feel “sticky” and they are hard to squeeze. • There are 12 different soil texture classes depending on how much sand, silt, and clay is in each sample and we use the “Texture Triangle” to define these classes

  15. Soils are grouped into 12 texture class names shown on this triangle

  16. Soil Quality Texture Nutrient Infiltration Water-Holding Aeration Tilth Capacity Capacity Clay Good Poor Good Poor Poor Silt Medium Medium Medium Medium Medium Sand Poor Good Poor Good Good Loam Medium Medium Medium Medium Medium Fig. 10.15b, p. 223

  17. Soil Moisture • Soil moisture is determined by several factors including, • Organic matter • Porosity • Capillarity

  18. Cation Exchange Capacity • Soils have a negative charge • Therefore, they repel negatively charged ions and attract positively charged ions • Cations can be exchanged within a soil • This is important to plant growth since some cations are essential (such as K+, Ca+, Mg+)

  19. pH • Acidity of Basicity of a soil • Determines which species can live in a soil • Plants impact soil pH • Pine trees lower soil pH

  20. Fertility • Plants require nitrogen and phosphorus for growth • The usable forms of nitrogen in soils are nitrate (NO3-) and ammonium (NH4+) • The usable form of phosphorus is phosphate (PO43-)

  21. Soil Formation Soils develop in response to • Climate • Living organisms • Parent Material • Topography • Time • (CLORPT)

  22. Climate • Two most important factors that determine climate are Temperature and Moisture and they affect • Weathering processes • Micro-environmental conditions for soil organisms • Plant growth • Decomposition rates • Soil pH • Chemical reactions in the soil

  23. Living Organisms • Intrinsically involved • Nutrient cycling – nitrogen cycle and role of Rhizobium, actionmycetes, etc. • Reduce size of leaf litter • Facilitate decomposition

  24. Parent Material • Refers to the rock and minerals from which the soil derives. • The nature of the parent rock has a direct effect on the soil texture, chemistry and cycling pathways. • Parent material may be native or transported to area by wind , water or glacier.

  25. Topography • Physical characteristics of location where soil is formed. • Drainage • Slope direction • Elevation • Wind exposure • Viewed on Macro-scale (valley) or micro-scale (soil type in field)

  26. Time • After enough time, the soil may reach maturity. • Depends on previous factors • Feedback of biotic and abiotic factors may preserve or erode mature profile.

  27. Destructional -WeatheringLandscapes broken down by chemical & physical processes & erosion Physical • includes temperature changes (freezing and thawing, thermal expansion), crystal growth, pressure, plant roots, burrowing animals • causes disintegration of parent material and facilitates chemical weathering Chemical • always in water • includes hydration, hydrolysis, oxidation, reduction, carbonation and exchange • examples : • oxidation of Fe to form limonite, deposited in joints, inhibits groundwater flow • hydrolysis of feldspars to form clay (kaolin) - forms infill for joints

  28. Mass wasting • Gravitational movement of weathered rock down slope without aid of water or wind (landslips) • transported material is called colluvium

  29. Destructional - Erosionmost significantly by running water • Sheet erosion • by water flowing down valley sides • severe when vegetation removed and geological materials uncemented • Stream erosion • materials brought downslope by mass wasting and sheet erosion are transported by streams • erosion by the streams - meanders etc

  30. Destructional - Karsts • Forms by dissolution of limestone - limestone is only common rock soluble in water - dissolved carbon dioxide in rain water • form highly variable ground conditions • formation of sink holes - when buried leads to surface subsidence

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