24: soil orders

pedogenic processes

environmental settings with certain processes are more dominant

processes occur along a precipitation and temperature gradient

lateralization location and soil

tropics, oxisol

common in warm moist regions; rapid weathering; most minerals dissolved or used; leads to very deep soils

podzolization location and soil

high latitudes, spodosol

produces gray soils (like ash); requires precipitation and acidic soils; common throughout boreal forests

gleziation location and soil

poles, gelisol

applies to waterlogged soils; anaerobic environment due to no oxygen; reduction of iron and manganese produces gray color

calcification location and soil

grasslands, mollisol

occurs where P < PET and grasses dominate; calcium salts precipitate into soil; white streaks/flecks appear

salinization location and soil

deserts, aridisol

pet > precipitation; dry climate; water moves up by capillary action; solutes transported from bottom to top

soil taxonomy

aridisol

andisol

mollisol

alfisol

ultisol

oxisol

spodosol

gelisol

entisol

inceptisol

histosol

vertisol

aridisol characteristics

DRY SOILS; occur in deserts; second most common soil globally (1/8th of planet); thin soil, little development, low organic matter

mollisol characteristics

ORGANIC RICH DARK, soft soils formed by grasslands;

pet > p leads to calcium accumulation beneath surface

up to 80 cm organic matter

very fertile may need irrigation

dry climate facilitates accumulation

alfisol characteristics

ALUMINIUM AND IRON RICH;

midlatitude deciduous forests

light e horizon; strongly weathered

thick clay-rich b horizon; can be fertile for agriculture

ultisol characteristics

ULTIMATE LAST SOIL (highly weathered)

common in tropics and subtropics; some iron oxidation

oxisol characteristics

OXIDE RICH, most weathered soil; strong oxidation and leaching; goethite common; thick tropical soils; mostly infertile

spodosol characteristics

ASH LAYER

occurs in forests with acidic leaf litter (boreal forests)

well-defined e horizon

leached components accumulate in b horizon

acidic, not fertile

gelisol characteristics

GELI = FROZEN SOIL

high latitudes. little development

vertical structure from cryoturbation

permafrost common

can be highly organic-rich

entisol characteristics

ENTI = NEW SOIL

very little development

no b horizon; extremely diverse

inceptisol characteristics

INCEPTI: YOUNG SOILS

inception of b horizon; horizons beginning to form

histosol characteristics

HISTO: ORGANIC TISSUE RICH accumulation of organic residues waterlogged soils prevent respiration ranges from peat to muck

vertisol characteristics

VERTI: SHRINK AND SWELL

clay-rich soils that shrink and swell

poor for construction; can form slickensides

andisol characteristics

ANDI: VOLCANIC SOILS

develop from volcanic parent material

light, organic-rich, high water-holding; highly fertile

arranging soils by weathering

weathering intensity increases with warmer and wetter climates; dry conditions limit development; anaerobic conditions promote organic matter accumulation

arranging soils by latitude

tropics: warmer, more precipitation, thicker soils; dry subtropics: thin soils; midlatitudes: moderate thickness

permafrost definition

soil permanently frozen for at least two consecutive years

permafrost importance

carbon storage; methane source; highly sensitive to climate

permafrost landform impacts on humans

structures fall apart as permafrost melts; roads crack; coastal erosion increases as permafrost weakens soil

human impacts on soil

great dustbowl
conversion of grasslands to agriculture; overgrazing and intensive agriculture degrade soils; drought + wind cause topsoil loss and dust storms

desertification of the sahel causes

loss of topsoil due to population growth, overgrazing, deforestation