Chapter 15 The Geography of Soils Flashcards
Soil
Natural surface layer of Earth
- Composed of mineral and organic matter (50%)
- Composed of air and water stored in pore space between soil particles (50%)
- Essential to life on Earth and society
- Plant growth/Habitat for animals and organisms
What factors form soil?
- Parent material (rocks)
- Climate
- Biological Activity
- Relief and Topography
- Time
Soil Forming Factors:
Parent Material
Weathered bedrock, rock fragments,and sediment determine soil types
Soil Forming Factors:
Climate
- Soils are influenced by temperature and precipitation
- Determine chemical reactions, organic activity, movement of water within soils
Soil Forming Factors:
Biological Activity
- Vegetative cover dies, decomposes, and
incorporates into soil - Burrowing insects and animals rearrange soils; incorporated after they die
- Microorganisms contribute
- Humus
- Decomposed organic matter; a vital component of soil
Soil Forming Factors:
Relief and Topography
- Influences the type of soil and its thickness
- Steep slopes; less soil
- Flat land; more soil
Soil Forming Factors:
Time
- Soils take thousands of years to develop
- Soils develop more quickly from sediment than bedrock
- Soils develop faster in warmer, humid climates
Soil Profile
Vertical section of soil layers
Soil Horizon
Individual layer of soil within a profile
Horizons
O, A, E, B, C, R
Soil Profile and Horizons:
O Horizon
- Top of soil profile
- Organic material
- Nutrient rich
Soil Profile and Horizons:
A Horizon
- Top soil; where plowing and pasturing occurs
- Dark colored
- Nutrient rich
Soil Profile and Horizons:
E Horizon
- Leached layer
- Clays, oxides, and organic matter are washed downward by water
- Light colored
Soil Profile and Horizons:
B Horizon
- Accumulation layer of clays,
aluminum, iron
Soil Profile and Horizons:
C Horizon
- Weathered parent material; regolith
- Plant roots and soil microorganisms
rare
Soil Profile and Horizons:
R Horizon
- Rock Horizon; Bedrock
- Unweathered parent material
Soil Taxonomy
An elaborate classification of soil types according to several parameters (most commonly their properties)
Soil Taxonomy:
Oxisol
Tropical Soils
Extremely weathered and easily eroded
Commonly found along the equator (South America, Africa)
Soil Taxonomy:
Aridisols
Desert soils
Soil Taxonomy:
Mollisols
Grassland soils
Most significant agricultural soils
Located in mid-latitudes, including N.A.Great Plains
Soil Taxonomy:
Alfisols
Moderately weathered forest soils
Geographically distributed from equator to high latitudes
Predominant in California’s Central Valley
Soil Taxonomy:
Andisols
- Found near volcanoes; volcanic ash
- Nutrient rich
Soil Taxonomy:
Histosols
- Soils with thick organic matter
- Formed in shallow lakes
- Associated with wetlands
- Peat and muck can form
- Poor drainage
- Nutrient poor; limited decomposition
