Soil Formation and Development

rocks and minerals (+ organic matter)

Soil ultimately came from

weathering

Rocks on the surface undergoes

pedogenic

Weathering products are subjected to _____ processes

Weathering

All physical and chemical changes produced in rocks, at or near the earth’s surface, by atmospheric agents.

Weathering

A biogeochemical process that involves both destruction and synthesis

physical weathering / disintegration

the breakdown of rocks and mineral particles into smaller by physical forces, without changing their chemical composition

increases, increases the rate of chemical weathering

physical weathering _____ the effective surface thus___

• temperature

• thermal expansion

• exfoliation

• abrasion

• frost wedging

• salt wedging

physical weathering

exfoliation

peeling away of outer layers of the rock

chemical weathering / decomposition

decomposes, dissolces and weakens rocks and minerals through chemical processes

K, Na, and Ca

___, ____ and ____ are highly soluble and readily leached in soils

Al

is extremely insoluble retained in soils

oxidation

loss of electron _______

reduction

gain of electron ______

weathering-limited environments

regolith/soil is unable to develop

weathering-limited environments

rock composition and structure determine the resulting surface form

transport-limited environment

regolith/soil is able to develop

transport-limited environment

materials released by weathering are subjected to further weathering

transport-limited environment

surface forms/structures are highly influenced by weathering and mass wasting

s= f(cl,O,R,P,T)

• SLIMATE

• ORGANISM

• RELIEF

• PARENT MATERIAL

• TIME

jenny’s equation

parent material (initial state of system)——soil formation——> soil (final state of system)

soil formation

passive soil formers

are represented by the constituents that sere as the source of the mass only and by the conditions that afffect the mass.

active soil formers

are the agents that supply the energy that acts upon the mass furnishing reagents for the process of soil formation.

• biosphere

• atmosphere

• hydrosphere

representative of active soil former

the changes of the soil-forming factors

The total change of any soil property depends on all

• transported

• formed

types of parent material

transformation

occur when soil constituents are chemically or physically modified or destroyed and others are sythesized from the precursor materials

translocation

involve the movement of inorganic and organic materials laterally within a horizon or vertically from one horizon to another

addition

inputs of materials to the developing soil profile from the outside sources

losses

materials lost in the soil profile

eluviation

movement of material out of the portion of a soil profile

illuviation

movement of material into a portion of a soil profile

leaching

washing out of eluviating material from the solum

enrichment

addition of material from the soil body

erosion

removal of soil material from the surface

cumulization

aeolian and hydrologic add. of particles in the surface

decalcification

reaction that removes CaCO3 from 2 or more horizon

calcification

accumulation of CaCO3 from 1 or more horizon

solonization

accumulation of sodium ion

solodization

leaching of sodium ion

lessivage

enrichment in clay

pedoturbation

homogenizing the solum in varying degrees

decomposition

breakdown of mineral and organic material

sythesis

formation of new material and organic species

melanization

darkening of light-colored material (admixture of OM)

leucinization

paling of soil horizon (removal of OM)

littering

accumulation of OM in the soil surface

humification

transformation or raw OM to humus

paludization

accumulation of deep deposits of OM (peat and mucks)

ripening

changes in organic soil with O2 (increase mo activity)

mineralization

releases of oxide solids through decomposition of OM

braunification

releases of Fe from primary materials (reddish soil)

gleization

reduction of Fe under waterlogged soil condition

soil profile

-the influence of soil forming factors and pedogenic processes

are all expressed along the

soil surface (O)

undecomposed organic debris, decomposed organic materials and humus

eluvial zone (E)

a light colored layer representing the zone of maximun leachin

eluvial zone (A)

a leached mineral horizon with a high proportion of organic matter (dark in color)

illuvial zone (B)

maximum zone of accumulation of weathering products such as silicate, clay, iron, aluminum etc.

illuvial zone (C)

relatively unaltered unconsolidated parent material

illuvial zone (R)

hard bedrock

surface soil

top soil

solum

surface soil + subsoil + ang pedogenically altered Substratum

solum

genetic soil

substratum

material below the solum

regolith

unconsolidated part of the earth’s crust

MECHANICAL WEATHERING

This means the rock is broken into smaller pieces without changing its chemical composition.

·        Wind – blows particles that hit and chip the rock

·        Rain – washes and erodes rock surfaces

·        Hail – ice pellets that hit rocks and cause cracks

·        Ice / frost – water enters cracks, freezes, expands, and breaks the rock

·        Heat & cold – repeated heating and cooling cause rocks to expand and contract, leading to cracks

- Causes of mechanical weathering -

FINE PARENT MATERIAL

After mechanical weathering, the rock becomes _______ — smaller fragments that are easier to chemically change.

• acids

• moisture

Factors in chemical weathering

SPONTANEOUS WEATHERING

This refers to natural breakdown of minerals once rock is exposed to air and water, even without strong acids.

• minerals, nutrients, ions

• oxides of iron and alumina

• silica

• silt

PRODUCTS OF WEATHERING

temperate climates

more 3 layer clays

tropical climates

more 2 layer clays

geochemical

purely chemical in nature

geochemical

occurs below the solum

pedochemical

occurs within the solum

pedochemical

influenced by biological activities/processes