Soil Genesis and Development

Factors affecting soil development

CLORPT

Hans Jenny's Equation (1941)

S=f(CLORPT)

Active Factors

Climate nd Organisms

Passive Factors

Relief, Parent material and Time

Parent Material

Initial state of soil system

Minerals

An inorganic substance that is produced by inorganic processes that have a definite chemical composition and physical configuration; building blocks of rocks

Rocks

An aggregate of Minerals

Basalt

Igneous

Intrusive Igneous Rocks

Extrusive Igneous Rocks

Sedimentary Rocks

Most abundant class of rock on earth's surface

Clastic Sedimentary rocks

Based on sizes

Chemical Sedimentary rocks

Biogenics/Organic Sedimentary Rocks

Metamorphic rocks

Undergo Physical condition; Either Sedimentary or Igneous

Residual

Transported

Water-transported

Wind-Transported

Gravity

Ice

Alluvium

River or Streams transported

Fluvial

River/Streams transported

Lacustrine

Lakes transported

Marine

Ocean transported

Wind-Transported

Mostly on arid/desert regions

Loess

Salt-sized particles

Aeolian

Sand-sized particles

Gravity

Water act as lubricant

Colluvium

Transported by gravity

Ice

Sediments transported by ice

Glacial drift/till

Transported by ice

Organic (Cumolose) Deposits

Climate

Temperature and Rainfall

Climate vs Weather

Long period Vs Short-term

Temperature

As for every 10 degrees celcius increase in temperature

Living Organisms

Mixing the soil or the process of bioturbation

Grassland Vs Forestland

High om than Forestland because Grassland has annual cycle of grass

Topography/Relief

Contours of the land

Topography/Relief

Toe slope has the highest organic matter content

Topography/ Relief

Top —> Bottom

Summit - Faster development of soil

Shoulder - Faster development of soil

Back slope - Slower soil development

Foot slope - Slower soil development

Toe Slope - High OM

Mottles

• mottles are spots or blotches of different colors found within a soil horizon.

• They indicate variations in soil conditions, especially related to drainage and aeration.

Time

The start of soil genesis

Chrono

Catena

Toposequence

Lithosequence

Climosequence

Biosequence

Basic Processes soil formation

• Transformation

• Translocation

• Addition

• Losses

Transformation

• Weathering (Physical, Chemical)

Physical Weathering

• Wetting and Drying

• Freezing and thawing/melting

• Heating and cooling (Extreme temp)

• Grinding and rubbing

• Unloading

• Organisms

Chemical Weathering

• Hydration

• Hydrolysis

• Carbonation

• Dissolution

• Oxidation

• Reduction

Translocation

Movement of organic and inorganic materials (e.g. leaching)

Addition

Addition of the outside material to the developing soil (e.g. organic material from falling plant leaves)

Losses

Materials lost in the profile (e.g. leaching, evaporation, erosion)

Transformation

When soil materials are modified, destroyed or synthesize into another form (e.g. mineral weathering, OM breakdown, arrangement of soil into structural aggregates, distintegrating and altering some to form various kinds of silicate clays)

Soil Profile

Is a vertical cross-section of the soil exposing all of its horizon.

Horizon

Described as the layer of the soil parallel to it surface

O Horizon

• Organic/Topmost layer

• Has greater than or equal to 20% organic

• Oi (undecomposed)

• Oe (moderately decomposed Organic Materials)

• Oa (Highly decomposed Organic Material)

A horizon

• Below O horizon

• Top soil

• Without O horizon, A has highest OM

E horizon

• Zone of eluviation (exit)

• Lighter color compared to layer above and below

• Commonly observed in areas with high rainfall and has sandy soil texture

• Mineral Horizon

B horizon

• Below A, E, or O

• Zone of Illuviation (into/Inside)

• Low OM compared A and O

C horizon

• Hard bedrock (Parent Material)

Solum

• O

• A

• E

• B

Regolith

All layers (Solum) above and including C

R horizon

• Hard bedrock (strictly not a horizon)

L (limnic) horizon

Occur only in certain organic soils and include layers of organic mineral material deposited in water or by aquatic organisms

W horizon

Layer of water found within certain soil profiles

V horizon

Layer dominated, non connected bubble-like pore that occuc in or near suface desert soils

M horizon

Mainly in urban soils in which manufactured root-liming materials form a horizontal, near continuous layer (Human Factor)

Horizon No