Soil Formation Factors
Climate
Organic activity
Relief
Parent material
Time
GEO 101, April 24, 2014
Finish soil formation factors
Soil classification
“CLORPT”
Organic matter in soil, metric tons per hectare
Plants control nutrients...what they use is recycled
If nutrient not used by plants, it is leached from soil if
there is enough precipitation.
180
240
Organic activity also includes soil microbes, fungi,
worms, burrowing rodents, ants
360
150
90
Relief: difference between highs and lows
shape of the land
Well
drained
soil on
hilltop if
not steep
Parent Material affects soil
Thin soil due
to erosion
Deep, poorly
drained soil
1
Comprehensive Soil Classification System
Time
Soil “taxonomy”
Takes hundreds –
thousands of years soil
County Soil Survey available from USDA
Young soils have poorly developed
horizons
Natural Resources Conservation Service
Mature soils have well developed
horizons
http://soils.usda.gov/
(was USDA Soil Conservation Service)
Old soils have overdeveloped “problem”
horizons with dense crusts or
hard-pans in “B”
Issued May 1980
Photos 1970
Climate is not a factor for the following soil orders:
Entisols: recent origin
Ex: river deposits
Andisols: “ando” = volcanic
Ex: volcanic ash and lava
Inceptisols: “inception”
Ex: soils just beginning to have a “B” horizon
Vertisols: “inverted”
Ex: clay or clay producing parent material
Histosols: “hist” = tissue
Ex: organic soils of wetlands
Vertisols shrink when dry
and swell when wet
2
Black soil near Montlimar and Hwy 90
Histosols
decompose and
lose volume when
exposed to air
Climate / Vegetation control only. Parent Material ignored!
Three major soil forming regimes
closely related to climate / vegetation type
Laterization
Podzolization
Calcification
Laterization soil forming regime
Warm wet climates (Af, Am, Cfa)
Broadleaf forests
Leaching is extreme
Silica and nutrients removed
A = oxic horizon, reddish (Fe and Al)
Oxisols and Ultisols
B enriched in “laterite (plinthite)”
clay-sized iron and aluminum
3
Podzolization soil forming regime
Cool humid climates (Df)
Coniferous forests
Acid litter  acid soil water
Everything dissolves except quartz
A = albic horizon, white like baking soda
Spodosols
B enriched in iron, aluminum, organics;
dark brown
Podzolization, deciduous forests, “Corn Belt”
Calcification soil forming regime
Semi-arid climates (BS, drier C & D)
Grasslands  high organic matter
Non-grasslands  low organics
Leaching minimal
A = “Mollic” horizon = “soft with humus”
dark colored
Mollisols and Aridisols
B = enriched nutrients and calcium
No loss to groundwater
“Bread baskets” of world
Irrigation
salinization issues
4
5