Soils Flashcards
Soil
thin surface made of mixture of weathered mineral particles, decaying organic matter, living organisms
How is soil made
process of weathering –> produces regolith (blanket rock) which consists of material from underlying rock. The uppermost layer of regolith is soil + has finely fragmented minerals
What are 5 soil forming factors
1) geologic
2) climatic
3) topographic
4) biological
5) time
Geologic Factor
1) Parent material - source of rock fragments that make up soil
2) Parent material –> affects soil that develops from it (shale –> fine dirt but sandstone –> coarse textured soil)
3) Passage of time –> significance of parent material reduces
Climatic Factor
1) temperature + moisture greatest significance to soil formation
2) high temperatures + high moisture –> accelerated formation of soil
3) moving water carries suspended particles that re-arrange chemical/physical component of soil
4) climate biggest factor in long run
topographic factor
1) Slope + drainage
2) top + bottom layer keep sinking
3) deepest soil is on flat land –> bottom soil develops faster than top soil eroded away
4) slope –> surface soil erodes faster than bottom soil develops
5) waterlogged soil –> lacks oxygen
Biological Factor
1) half minerals + half air/water + only tiny part is organic matter
2) root systems of plants –> help provide passage for drainage
3) small animals tunneling –> provides passage for air + water
4) earthworms –> tunnels aid drainage, constant movement makes soil crumbly which plants like, digestive actions of worms increases porosity –> reduces erosion, release nutrinets into soil by excretion, promotes nitrification
Soil components
1) inorganics (45%)
2) organics (5%)
3) air (25%)
4) water (25%)
Time Factor
1) soil forming processes very slow
2) warm, moist environment is best
3) soil changes very slowly BUT we can see effects of erosion
4) dimension of human time –> soil is unrenewable
Inorganic Materials
1) Mainly mineral matter
2) Sand + Silt
3) smallest particles are clay = form small pellets that attract cations which necessary plant nutrients
Organic Matter
1) Plant roots + decaying matter
2) many micro-organisms that rearrange soil + play role in nutrient cycling
3) litter = leaves, twigs, stalks –> decomposition
4) humus = remnant of decomposed residue –> black gold –> loosens structure of soil + facilitates root development
Soil Air
1) half volume made of pore spaces
2) interstices (passageways) for air/water
3) soil air saturated with water vapor + carbon dioxide, poor w. in oxygen
Soil Water
1) comes from percolation of rainfall + snowmelt
2) some added from groundwater –> rises via capillary action
3) 4 types of soil moisture
- gravitational water = water sinking from above and going through soil, only stays for a short time (gravitational water causes eluviation + illuviation)
- capillary water: remains after gravitational water drains –> moisture held at surface of soil by surface tension –> principle source of moisture for plants
- hygroscopic water = thin film of moisture bound to soil particles by adhesion –> adheres so tightly that plants cannot use it
- combined water = held in chemical combination with soil minerals, least available
Field capacity
amount of water that remains in soil after gravitational water drains away
Leaching
water leeches nutrients bc it dissolves them + carries nutrients downward
Eluviation/Illuviation
(E = exit, I = influx)
Eluviation = takes fine minerals from topsoil + moves it downward
Illuviation = minerals taken downward are deposited at lower level
Soil properties: color
1) color = product of stains usually by metal oxides or organic matter
2) black/dark brown = high humus content
3) reddish/yellowish - high iron
4) gray/blue = poor drainage
Soil properties: texture
no soil has uniform particles –> texture determined by relative amounts present
Texture Triangle = gives classification scheme for soil texture
even textured mix (loam) most productive for plants
Soil Properties: Structure
1) Soil aggregates into clumps called peds
2) Peds classified as spheriodal, platy, blocky, prismatic
3) better drainage –> intermediate sized peds while fine/massive peds inhibit it
4) porosity = measure of soil’s capacity to hold water/air
5) permeability = ability of soil to transmit water through it
Soil horizons
1) distinct layers = horizons w. different characteristics
2) soil profile = vertical cross section of earth’s surface
Horizons
1) O horizon = surface layer of organic matter = litter from dead plants/animals
2) A horizon = topsoil = mineral horizon w. organic matter (darker than surrounding horizions)
3) E horizon = lighter in color, zone of eluviation + leaching
4) B horizon = accumulation of clay, iron, aluminum from above
5) C horizon = partially altered parent material
6) R horizon = unweathered parent material (bedrock)
O, A, E, B = soil
O, A, E, B, C = regolith
**R = bedrock*
Pedogenic (“soil forming”) Regimes
1) Laterization
2) podzolization
3) gleization
4) calcification
5) salinization
Laterization (warm moist climates –> forest, shrub, savanna)
1) Named for brick-red soil color produce
2) found in tropics + subtropics (warm regions)
3) rapid decomposition of matter, fast weathering of parent material, rapid leeching of minerals esp. silica from soil
4) most rapid nutrient cycle + little humus
5) ORGANICS = LOW
6) LEACHING = HIGH
7) ILLUVIATION (INFLUX) = HIGH
Podzolization (podzols)
1) named after gray soil it produces (podzols - acidic, gray)
2) occurs in regions where vegetation has limited nutrient requirements + acidic plant litter –> mid + high latitudes w. coniferous cover
3) slow chemical weathering + effective leeching
4) retarded humus bc lack of micro-organisms
5) shallow, acidic soil called podzols + high silica content –> gray color
6) ORGANICS: Medium
7) LEACHING: HIGH (lots of rain)
8) Illuviation: High (iron accumulates)
Gleization (gleiy soils)
1) waterlogged areas = muddy ground
2) region w. high water tables like around great lakes
3) gley soils = slow decomposition w. high organic matter bc bacteria lack oxygen
4) anaerobic environment causes iron to be reduced + carried away –> soil becomes iron poor + gray over time
5) too acidic + oxygen poor to be productive for anything but water tolerant plants
6) ORGANICS: HIGH (anaerobic –> acidic)
7) LEACHING = LOW (standing water = no movement of water)
8) ILLUVIATION = LOW (no movement of water)
Calcification (around deserts, not deserts themselves) CaCO3 forms
1) moderate climate –> short lived leaching
2) dominant in drier praries of NA, steppes, savannas/steppes
3) Lack of rain –> Capillary action + lack of eluviation –> minerals concentrated in soil where calcification occurs
4) little clay formed + productive soil bc of humus
5) Organics: RANGES
6) Leaching: LOW (lack of precip)
7) Influx: MODERATE capillary action bringing influx of nutrients
Salinization (Salt forms DESERTS)
1) arid + semiarid –> common in poor drainage areas
2) intense evaporation draws moisture upwards, leaving salt on surface –> making soil brilliant white color
3) support very little life bc of high amount of chlorides, sulfates, sodium
4) Organics = LOW
5) Leaching = LOW (no water/rain + salt layer prevents water from going down)
6) Illuviation = High, capillary reaction –> bringing up salt
Inceptisols
Inceptisols - not developed enough to have horizons, primary eluvial soil + most common in tundra + mountain areas
Entisols
least well developed of soil, very widespread + no correleation with moisture/temperature
Andisols
volcanic ash, not highly weathered bc recently deposited, found mainly in Japan, Indonesia, South America, wheat lands of Washington, Oregon, Idaho
Gelisols (Permafrost)
young soils w. minimal profile development,
develop slowly bc of cold temperatures + frozen conditions, found in Arctic + subarctic regions
BIOME: tundra + boreal forest
Histosols (organic soils in wet sites)
1)small fraction of land area
2) occur in waterlogged environments that experienced Pleistocene glaciation in mid/high latitudes
3) black, acidic, fertile ONLY for water-tolerant plants
4) can be very productive if drained
5) area surrounding great lakes + southern florida/louisiana
Aridisols (dry climates)
1) 1/8 of soil is aridisol
2) thin sandy profile lacking organic matter
3) light in color + unproductive bc lack of moisture
4) threat of salt accumulation
Vertisols (Swelling + Cracking clays)
1) contain large quantity of clay
2) exceptional capacity for absorbing water –> when moistened swells + expands
3) as it dries cracks form
4) cycle repeats producing churning effect that mixes soil
5) requires alternating wet + dry climate to form
6) found in eastern Australia, India, small part of East Africa
7) very fertile BUT difficult to till –> often uncultivated
Mollisols (Dark, soft grassland soil)
1) presence of mollic epipedon –> contains abundant humus + soft
2) transition soil in regions not dominated by humid/arid conditions
3) common in mid-latitude grasslands + central Eurasia, Great Plains, Argentina
4) most productive soil order –> made from loose parent material instead of bedrock + nutrients retained within reach of plants –> lack of leaching
5) favored habitat for worms
Alfisols (Clay-rich B horizons, High Base status)
1) most wide-ranging + mature soil
2) occurs in low + midlatitudes
3) found in variety of temps + moisture
4) associated w. transitional environments + varied global distribution
5) 2nd most fertile soilU
Utisols (Clay-Rich B Horizons, Low Base Status)
1) more thoroughly weathered than Alfisols + leached of nutrients
2) experienced more mineral alteration than any soil in midlatitudes
3) Alfisols –> degenerate into utisols
4) Humid subtropical climates + restricted to Southeast US
Spodosols (Cool, Forested Zones)
1) spodic sub-surface horizon (dark reddish layer where organic matter, iron, al accumulate)
2) INTERFTILE –> leached of nutrients + acidic
3) do not retain moisture –> common in coniferous forest w. subarctic climate
Oxisols (highly weathered + leached)
1) most weathered + leached soil
2) ancient landscapes in humid tropics like Brazil + equatorial Africa
3) product of laterization
4) deep soil BUT not very fertile –> vegetation does good job of cycling limited nutrients but without vegetation nutrients would quickly leach out
Saltwater intrusion
taking too much water from aquifer –> brings in ocean water in coastal areas into water table –> salinization
