geog 1113: landform geography soils july 2, 2013
TRANSCRIPT
What is Soil?• Uppermost layer of Earth’s surface with mineral
& organic matter able to support plants
• Transition between atmosphere & rocky Earth
• Provides plants with physical support, nutrients & water
• Plants support soils by anchoring them to Earth
Basic Soil Properties
– Inorganic Material – minerals - natural elements or compounds w/crystalline structure – silicon, aluminum, iron, potassium, calcium, etc. common in soil minerals
– Organic Matter – bacteria & fungi break down remains of plants & animals to form humus – helps soil hold water and increases fertility
Basic Soil Properties• Water – from rain & snow
– Losses to evapotranspiration
– Drainage through soil, leaving air pockets
– Capillary Action – attraction to soil particles
– Surface tension holds some water in soil
– Field capacity – max. water capacity of soil
– Soil-Water Budget – balance of soil-water gains & losses
Basic Soil Properties
• Air – most air in soil is carbon dioxide
– Plants give off CO2 during respiration & take it in during photosynthesis
– Less air in wet soil because of water
Soil-Forming Processes
• Soils form & evolve through sequence of interrelated pedogenic (soil-forming) processes:
– Soil Additions
– Translocations
– Soil Depletions
– Transformations
Soil-Forming Factors
• Factors that consistently affect how soils form
– Parent Material
– Climate
– Organisms
– Relief
– Time
Parent Material
• Sediment in which soil forms – related to geology of the region
• Residual Parent Material – sediment from rock that weathers in place
• Regolith – small fragments of weathered rock
• Transported Parent Material – carried by wind, water, or glaciers from where it weathered
Climate
• Temp & moisture influence the kind & rate of biological and chemical reactions in soil
• More reactions in warm, wet conditions, so thicker, more developed soils
• Wetter soils have more eluviation & deeper illuviation b/c of water percolating downward
Organisms
• Plants & animals that reside in soil
• They acquire food from soil & regulate its environment
• Bioturbation – mixing of soil by plant roots and burrowing animals
• Earthworms important as soil recyclers
• Micro-organisms decompose organic matter to humus
Relief
• Differences between highs and lows of landscape – Mts are high relief, plains low relief
• Soils thin & poorly developed on steep slopes
• Sediment eroded more on steep slopes
• Sediment deposited more on areas of low relief where soils deeper & more developed
Time
• Longer time on a stable surface allows for greater soil development
• Soil in a 10,000-yr-old floodplain more developed than soil on 2000-yr-old sand dune
Measurable Soil Characteristics
• Physical Properties to Distinguish Soil Types:
– Color
– Texture
– Structure
– Soil Chemistry
– Soil pH
Soil Profiles• Soil processes lead to vertical organization in
soil, layers in a profile visible in cross-section
• Soil Horizon – distinct layer in soil profile
• Horizons blend into each other, no sharp boundaries
• Soil profiles vary in different regions of Earth, depending on soil-forming factors
Soil Science and Classification
• Goal of soil science to understand Earth’s soils in order to preserve & efficiently utilize them
• Classification in US based on soil taxonomy: color, texture, structure & mineral content
• Soil Order – highest level in soil taxonomy
• 12 soil orders occur on Earth
• Soil orders subdivided into many categories