Soil Science - 2. Weathering and Soil Formation

Rocks

soil material from minerals

Minerals

naturally occurring inorganic substances

Igneous rock

solidification of molten magma

Granite

felsic intrusive
rich in SiOAlNaK

Peridotite

denses coarse grained
Olivine and Pyroxene

Gabbro

coarse grained/dark colored
Plagioclase and Augite

Basalt

mafic extrusive
rich in MgFe

Diorite

intrusive
Biotite and Hornblende

Sedimentary rock

accumulation or deposition of small particles
cementation of particles on the floor of bodies water

Shale

clastic clay size
flat sheets

Sandstone

clastic
sand accumulation

Limestone

calcium carbonate
shell, coral, fecal
precipitation
no Mg

Dolomite

carbonate, dolomite material
CaMg(CO3)2

Conglomerate

coarse grained >2mm

Chert

hard fine grained
crystals of quartz
SiO2

Breccia

broken fragments

Metamorphic rock

metamorphism of original rock

Amphibolite

non-foliated
foliated=thin sheets
recrystallization
hornblende & plagioclase

Hornfels

fine grained non-fo
contact metamorp
baked

Novaculite

fine grained siliceous

Marble

non-foliated
metamorphism of limestone/dolomite

Gneiss

banded
quartz or feldspar

Schist

well developed mica
Mica=group of silicate minerals
i>phyllite,gneiss

Phyllite

very fine grained mica
i>schist,slate

Slate

foliated
metamorphism of shale

Parent material

unconsolidated chemically weathered
pedogenic process
initial state

Residual Parent Material

type of PM
long and intense weathering
landscape=stable
in situ
composed of 3 class

Transported Parent Material

type of PM
loose or surficial
basis of agents for movements and deposition

Alluvium

water transported; close to river banks

Lacustrine

water transported; lakes (taal lake)

Marine

water transporter; oceans whereas waves contribute

Eolian deposits

wind transported sand-size, sand dunes for short distances

Loess

wind transported silt-size for longer distances

Volcanic ash

wind transported ash, light weight for longest distances

Colluvium

transported due forces of gravity/erosion
coarse

Glacial till

moving ice sheet

Cumulose

type of PM
organic deposits developed

Climate

most important factor influencing physical and chemical properties of soil

Precipitation

causes leaching

Climate

the long-term pattern of weather in a particular area
warm moist > rapid plant growth > ↑OM

Bioturbation

mixing of decompose with the upper part soil

Relief

orientation of land respect to the direction of the sun

shallow slope

north facing slope aspect

Soil formation

age of the soil; whereas constant age is observed

Soil thickness

major indication of soil age

Human

directly/indirectly affect the soil formation and considered the 6th factor

Soil Formation

“genesis” continuous but slow process

Transformation

weathering of primary minerals whereas PM > Silicate and decomposition of OM whereas decomposes and are incorporated

Physical weathering

breakdown of minerals by physical forces

Chemical weathering

decomposed, dissolved or loosed by chemical processes; “biogeochemical”

Wetting and Drying

wet soils > prone > swelling > shrinks

shrinkage and swelling

Freezing and Thawing

water expands when frozen > pushes soil > breaks

Heating and Cooling

extreme temperature > soil expands > contracts

Grinding or Rubbing

grinding against > disintegration (abrasion by water)

Unloading

pressure > compressed

Organisms

roots > pushed > soil

Oxidation

oxygen combines > other elements > softening > easily to break

rusting

Dissolution

minerals > dissolve directly > water > ions carry away

Carbonation

CO2 & rainwater > forms carbonic acid > reacts with the minerals

Hydrolysis

water molecules split = H+ & OH-

feldspar > clay mineral > crumbles easily

Hydration

minerals absorb water > expands > stress > disintegration

Translocation

transfers of soil constituents involving inorganic and organic form calcareous hardpan

Downward translocation

organic food material is manufactured by leaves and is translocated downward to stem and the roots for consumption and storage
-stops where the wetting front stops

Upward translocation

It takes place mainly during the germination of seeds, tubers etc., when stored food after being converted into soluble form is supplied to the upper growing parts of the young seeding till it has developed green leaves
- stops at the soil surface when water evaporate

Additions

inputs of materials to the soil profile
as plant life begins > om starts to accumulate
OM increases CEC

Losses

most losses occur by leaching;
water moves > dissolves minerals > transports > soil
grazing
wet soil > N > gas > lose in atmosphere

Laterization

removes silica
leaving sesquioxides to concentrate in the solum
most common in tropics

Calcification

precipitation and accumulation of (CaCO3)
B horizon enriched with calcium carbonate
most common in warm, semi-arid; grassland vegetation

Salinization

accumulation of salts near the soil surface
common in arid and semi-arid

Podzolization

formation of podzols
leached soil < cool, humid places
leaches solum (opposite of calcification)
creates the sublayer in A horizons
cool and moist climate; pine forests

Gleization

formation of gley horizon
accumulation of OM in upper layer
blue-gray