Transcript How do soils form?
How do soils form?
Soil Profiles
How do you start describing the soil?
What do you see?
What is different from top to bottom?
How deep do roots go?
• • •
Soil Profile Descriptions
Soil Profile - A vertical section of the soil extending vertically through all its horizons and into the parent material.
Soil Horizon - A layer of soil, approximately parallel to the surface, with properties that differ from the horizons above or below it – the properties (characteristics) are produced by soil forming processes.
Soil Layer - A layer in the soil deposited by a geologic force (wind, water, glaciers, oceans, etc.) and not relating to soil forming process.
E O
( humus or organic Decomposing leaves and lots of )
A
organic matter (topsoil) Contains lots of roots, and minerals for growing plants ( eluviated layer or EXIT layer ) Materials, minerals, organic matter, and clays exit the soil profile
B
(subsoil) Minerals from upper horizons stop here
C
(parent material) Earth’s surface that soils developed from
R
(bedrock)
Top Soil Subsoil Parent Material
A Horizon B Horizon C Horizon
Remember the Ideal Profile Using this Pneumonic Device:
O
ur
A
unt
E
thel
B
akes
C
ookies
R
egularly
Organic (O) Horizons
• • O horizons or layers: Layers dominated by organic material.
Identification Criteria – >20% organic matter – – – Dark color ( Feels ‘Squishy” Identifiable dead leaves, grass, etc. accumulated at surface
A Horizons
• • • • • Referred to as topsoil Typically ranging from 6-30 centimeters thick Mineral horizon formed at the surface or below an O horizon. Characterized by an accumulation of well decomposed organic matter intimately mixed with the mineral fraction.
Identification Criteria – – – – Mineral soil material Mix of well decomposed organic matter and mineral material Surface mineral horizon Typically dark in color-darker than underlying horizons
A Horizon
A Horizon
• • • • •
E Horizons
Mineral horizon in the upper part of the soil typically underlying an O or A horizon. Light colored, leached horizons ranging from not being present to several centimeters thick Light color due to the natural color of the mineral grains.
Formed by weak organic acids that strip coatings from mineral grains. Field Identification – Zone of eluviation - removal of clays, Fe, Al, and humus – – Lighter in color than over or underlying horizon Near surface, below O or A horizons and above a B horizon
E Horizon
E Horizon
B Horizons
• • • Referred to as subsoil. The zone of accumulation (or illuviation) within the soil. Field Identification – – – – Subsurface horizon formed below an O, A, E horizon and above the C horizon Formed as a result of soil forming processes Expressed often by color Illuvial concentration-zone of accumulation
B Horizon
Bg Horizon
C Horizon
• • • Referred to as parent material. These horizons and layers are little affected by soil forming processes (unweathered geologic material).
Field Identification – Little affected by soil-forming processes – Geologic layering – Color of unweathered geologic material
R Horizon
• • Hard rock Field Criteria – Can not dig it with a shovel or backhoe
• • • • • • • • • Decompose Bedrock Developed Soil Eluviated Horizon E Horizon Horizon Humus Leaching Minerals
Vocabulary
• • • • • • • • • Organic Matter Organisms Parent material Soil Soil Profile Subsoil Topsoil Transform Weathering
• • • • • • A Horizon B Horizon C Horizon R Horizon O Horizon Soil Monolith