FINAL EXAM - Soils

Soil

• Regolith = soil + saprolite

• Bedrock

Soil Components

• Inorganic minerals

• Water & air

• Organic matter

• Living organisms

Soil Profiles

• O horizon

  • Debris

• A horizon

  • Zone of leaching

  • Top soil

  • Eluviation → loss of material

  • E horizon → not always present, less organic material than A

• B horizon

  • Zone of accumulation

  • Subsoil

  • Illuviation → accumulation of material

• C horizon

  • Partially weathered material

  • Saprolite

• K horizon

  • not always present

  • carbonate layer

• R horizon

  • Bedrock

• High depths = Low weathering

Soil horizonation

Development of horizon layers. Linked to soil forming

Landscape Armoring

When thick & stable soil profile has developed. Slows weathering

Soil Development

• Inputs from outside and within ecosystem

• Physical + Chemical weathering

• Translocation of material

• Decomposition of OM

Soil Texture

• Provides info about:

  • water flow potential

  • water holding capacity

  • fertility potential

  • suitability for urban use

• Clay, silt, sand → equal amounts creates loam

• OH mostly silt loam

Soil development factors

• Parent material

  • Mafic parent rock → high clay, low sand, higher pH (still acidic), high nutrient. smectide & vermicullite

  • Felsic parent rock → high sand, low clay, low pH, low nutrient. illite

• Climate

  • Tropical Forest → high rainfall = thick soil & high weathering

  • Subtropicla → weakly developed soil

  • Temperate → strongly but thinly weathered

  • Tundra → Frozen soil

• Physical & Chemical Processes

  • Physical → breaks rocks intro small mineral particle ( frost shattering, root wedging, shrink/swell)

  • Chemical:

    • Dissolution of Carbonates → CO2 released from decaying organic matter & dissolved rainwater (creates underground caverns)

    • Oxidation & Hydration → Fe in minerals combined w oxygen & water to form hydrated iron oxides (rust)

    • Hydrolysis → responsible for formation of clays. Fledspar reacts with acidic water to form clay minerals

• Organisms

  • Decay of fresh OM makes humus & dissolved OM → both can be become mineral matter through absorption

• Topography

  • Weathering limited → steep slopes (soil slides down). no time before slopes loose material

  • Transport limited → a lot of time but limited transport bc of low surface

• Time

Peds

aggregates of soil particles that give soil visible structure

Cutans

Coating on soil particles → form through illuviation

Mottled fabric

Color variation represent oxide conditions

• oxidized (+3) = red

• reduced (+2) = white/gray

Soil nodules

localized deposits of material. Represent translocation of material

Role of plants in weathering

• Physical weathering → roots breakup substrates but can also bind weathered material.

• Chemical weathering → Release H+ to attack soil minerals. Causes soil minerals to disintegrate and create negative surface charge

12 orders of soil taxonomy

• Well weathered soils

  • Alfisols

  • Spodosols

  • Ultisols

  • Oxisols

• Lightly weathered soils

  • Inceptisols - insufficient time

  • Aridisols - climate

  • Entisols - unweatherable parent material

• Special Enviroment

  • Gellisols - tundra

  • Histosol - swamp

  • Mollisols - grassland

  • Vertisols - swelling clays

  • Andisols - volcanic

Alfisols

• Semiarid-moist areas. Hardwood forest (10% of US, Midwest)

• High productivity = agriculture

• 35% base sat

• kaolinite, smectide, vermiculite, illite

• Moderate weathering that leaches clay minerals out of surface layers

Spodosols

• Moderate rainfall. Conifer forests (4% of US, NE)

• Needles of pines generate acids on soils = leaching (of A horizon)

• Low pH

• kolinite, smectide, vermicullite, illite, gibbsite

Ultisols

• Cold, humid, coniferus forests (8% of US, South) → red soils

• Less than 35% base sat

• Intense weathering & leaching

• Low pH, low nutrient

• kolinite, Fe, illite, vermiculite, quartz

Oxisols

• Tropical Rainforest (8% of US, PR and HW)

• Highly weathered

• Low CEC

• Red or yellow = high Fe (higher than ultisols)

• Quarts, clay minerals, and OM

• Low nutrients = low productivity

• Kaolinite, gibbsite, Ti minerals

Inceptisols

• High elevation areas like Appalachians (17% of US)

• Insufficient time for weathering → poorly developed

Aridisols

• Desert, dry, hot (12% of US, SW)

• Insufficient climate for weathering

• Dry regions, low rainfall → sometimes upward movement due to evaporation

Entisols

• Sandy parent material (16% of US, West)

• Hard to weather parent rock → areas of recently deposited material

• Causes: erosion & deposition

Gelisols

• Tundra (9% of US, Alaska)

• Ice, high latitude, low vegetation

• Permafrost → frozen 2m of soil surface

• No A or B horizon

• Not fertile

Histosols

• Swampy areas ( 1% of US, Fl & MI)

• Mainly OM → soil develops in water clogged conditions

• Low pH. low nutrient

• Smectide and Illite

Mollisols

• Grasslands, intermediate precipitation (7% of US, Middle)

• High nutrient, High OM

• Soil nodules composed of calcium carbonate

Vertisols

• Swelling clays (3% of US, Mississippi)

• Seasonal shrink and swell

• Peds form due to soil distortion

• Smectide & Vermiculite

Andisols

• Volcanic ash, cool areas, moderate precipitation (1% of US, Pacific NW)

• Weakly weathered soil with volcanic glass

• Productive soils