SFI 100 Geology and Forest Soils

• Weathering

  Breakdown and alteration of rocks and minerals
• Importance of Weathering

  • Prerequisite to soil formation
  • Results in formation of sand, silt, clay
  • Releases nutrients for plants
  • Contributes to physical properties of soil
• Types of Weathering

  • Physical
  • Chemical
  • Biological
• Physical Weathering

  Rocks or minerals are broken down to smaller fragments
• Mechanisms of Physical Weathering

  • Frost wedging / action
  • Growth of foreign crystals
  • Thermal expansion and contraction
  • Pressure release upon unloading
  • Abrasion
• Chemical Weathering

  Alteration of chemical and mineralogical composition, products may be another solid form or a solution
• Mechanisms of Chemical Weathering

  • Hydrolysis
  • Oxidation
  • Reduction
  • Carbonation
  • Hydration and Dehydration
  • Solution
• Biological Weathering

  Disintegration and decomposition of rocks and minerals due to physical and chemical agents of organisms
• Mechanisms of Biological Weathering

  • Root action
  • Lichens formation
  • Chelation
• Goldich Stability Series

  Used to determine the rate of weathering
• Products of Weathering

  • Quartz - Sand grains
  • Feldspars - Silicate clays - K, Ca, Na
  • Muscovite - Silicate clays - K
  • Ferromagnesian minerals - Secondary minerals - Fe, Mg
• Soil

  Layers of generally loose mineral and/or organic material affected by processes
• Soil is not dirt
• Functions of Soil

  • Media for plant growth
  • Modify atmosphere - emission and absorption of gases and dust
  • Habitat
  • Absorb, hold, release, alter, purify water
  • Process recycled nutrients
  • Serve as engineering media for construction
  • Preserve / destroy artifacts
  • Filter water before it moves into an aquifer
• Forest Soil

  Currently under the influence of forest vegetation
• Soil Profile

  Vertical, cut from topmost layer
• Soil Horizon

  Horizontal, layers of soil with distinct properties from each other
• Master Horizons

  • O
  • A
  • E
  • B
  • C
  • R
• O Horizon

  Organic horizon on top of mineral soil, composed of Oi (fresh organic material), Oe (partially decomposed), Oa (humidified)
• A Horizon

  Topmost mineral horizon, dark colored, granular structure, friable, coarse-textured than the horizon below, zone of maximum organic matter accumulation and biological activity
• E Horizon

  Zone of maximum eluviation (movement of materials - clay, and Fe and Al oxides OUT of the horizon)
• B Horizon

  Finer-textured, clayey with blocky structure, reddish in color, zone of maximum illuviation (movement of materials - clay, and Fe and Al oxides INTO the horizon)
• C Horizon

  Referred to as the parent material, blocky to prismatic structure, hard and sometimes brittle but can still be dug by digging tools
• Solum

  Horizons A + B
• Regolith

  Horizons A + E + B + C
• Topsoil

  0 to 20 cm depth, plow layer
• Subsoil

  Beneath topsoil
• How is soil formed?

  • Addition
  • Transformation
  • Transfer
  • Losses
• Factors of Soil Formation

  • Climate
  • Organisms
  • Relief
  • Parent Material
  • Time
• Climate

  Temperature and rainfall are critical, affect the rate of soil processes, weathering, decomposition, and impact the type of vegetation in an area
• Organisms

  Plants and animals from micro to macro, alter physical properties of soil like pore spaces, weathering through root exudates and root action
• Relief

  Elevation, slope, aspect, exposure, affects the stability of land surface for other soil-forming factors and processes to initiate and continue soil formation, determines the amount of moisture and exposure the area receives
• Soil Series / Catenas

  Related soils of about the same age, derived from similar parent, similar conditions, arranged into sequence of increasing wetness
• Parent Material

  Has a great influence on the resulting property of the soil
• Types of Parent Material

  • Sedentary - rocks (igneous, sedimentary, metamorphous)
  • Transported - Gravity (Colluvium), Water (Alluvium - river, Lacustrine - lake, Marine - Ocean), Ice (Glacial), Wind (Eolian)
• Time

  Determines duration the parent material was subjected to the other soil-forming factors, the longer the time under stable conditions, the more developed and old the soil, catastrophic events reset soil formation
• Soil Taxonomy

  Comprehensive classification system developed by US Department of Agriculture Soil Survey Staff, based on soil properties that can be objectively observed or measured, with nomenclature giving a definite connotation of the major characteristics of the soil
• Taxonomical Hierarchy

  • Order
  • Suborder
  • Great group
  • Subgroup
  • Family
  • Series
  • Phase
• Soil Orders

  • Entisol
  • Inceptisol
  • Alfisol
  • Ultisol
  • Oxisol
  • Spodosol
  • Aridisol
  • Histosol
  • Mollisol
  • Vertisol
  • Andisol
  • Gelisol
• Entisols

  Recently formed, no diagnostic horizons, found in any climate on very recent geomorphic surfaces