Soil Formation Soil is an important natural resource

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Soil Formation �Soil is an important natural resource �It is found almost everywhere on

Soil Formation �Soil is an important natural resource �It is found almost everywhere on Earth �Exactly what is it?

Soil Formation �Soil • Loose covering of broken rock particles and decaying organic matter

Soil Formation �Soil • Loose covering of broken rock particles and decaying organic matter (humus) overlying the bedrock of Earth’s surface. • Decaying organic matter is the decomposition of vegetation and animal remains in varying stages.

Soil Formation �Soil is the result of chemical and mechanical weathering and biological activity

Soil Formation �Soil is the result of chemical and mechanical weathering and biological activity over long periods of time. �The soil-forming process begins when weathering breaks solid bedrock into smaller and smaller pieces.

Soil Formation �Bacteria, fungi, and insects begin to live in the weathered materials. �More

Soil Formation �Bacteria, fungi, and insects begin to live in the weathered materials. �More nutrients are added to the weathered materials by the death and decay of organisms.

Soil Composition � Soil forms in layers during the process of its development. �

Soil Composition � Soil forms in layers during the process of its development. � The parent rock is the solid bedrock from which weathered pieces of rock first break off. � The smallest pieces of weathered rock, along with living and dead organisms, remain in the very top layer. � Rainwater seeps through this top layer of materials, dissolves soluble minerals, and carries them into the lower layers of the soil.

Soil Composition � Residual soil is soil located above its parent bedrock. � Transported

Soil Composition � Residual soil is soil located above its parent bedrock. � Transported soil is soil that has been moved to a location away from its parent bedrock by agents of erosion, such as running water, wind, and glaciers. � The parent bedrock determines what kinds of minerals a soil contains. � The parent rock and climatic conditions of an area determine the length of time it takes for soil to form.

Soil Profiles � What is a soil profile? • A vertical sequence of soil

Soil Profiles � What is a soil profile? • A vertical sequence of soil layers • A soil horizon is a distinct layer, or zone, within a soil profile. • There are three major soil horizons: A, B, and C.

Soil Horizons � (O) Organic matter � (A) Top soil with high concentration of

Soil Horizons � (O) Organic matter � (A) Top soil with high concentration of organic matter & humus � (B) Subsoil enriched with clay minerals (Fe & AL) � (C) Weathered parent rock

Topography �Topography is the surface features of a place or region (e. g. valleys,

Topography �Topography is the surface features of a place or region (e. g. valleys, mountains, rivers, etc. ) �The topography of a region affects the thickness of developing soil. �Soils on slopes tend to be thin, coarse, and infertile. �Soils formed in lower areas, such as in valleys, are thick and fertile.

Soil Types � Polar Soils • Form at high latitudes and high elevations •

Soil Types � Polar Soils • Form at high latitudes and high elevations • Located in Greenland, Canada, Antarctica • No distinct horizons, very shallow soil • Just below the soil the ground is permanently frozen-known as permafrost Permafrost in Denali

Soil Types �Temperate Soils • Lots of variation • Support forests, grasslands, prairies •

Soil Types �Temperate Soils • Lots of variation • Support forests, grasslands, prairies • Amount of rainfall determines what grows in this type of soil �Grasslands-lots of humus-soil is rich and fertile �Forests-soil is less deep/less fertile, containing clays and iron oxides (Eastern US) �Prairies-dry soil-lots of grasses and bushes

Soil Types �Desert • • • Soils Very little precipitation High levels of salts

Soil Types �Desert • • • Soils Very little precipitation High levels of salts Limited vegetation Little or no organic matter Very thin topsoil (A horizon) Light colored and coarse soil

Soil Types �Tropical Soils • High temperatures, heavy rainfall • Soil is intensely weathered,

Soil Types �Tropical Soils • High temperatures, heavy rainfall • Soil is intensely weathered, infertile • Source of ores (iron), but not great for growing plants

Soil Types

Soil Types

Soil Textures Particles of soil are classified according to size as being clay, silt,

Soil Textures Particles of soil are classified according to size as being clay, silt, or sand, with clay being the smallest and sand being the largest. � The relative proportions of these particle sizes determine a soil’s texture. � The texture of a soil affects its capacity to retain moisture and therefore its ability to support plant growth. �

Properties of Sand, Silt, & Clay

Properties of Sand, Silt, & Clay

Soil Textures � To determine the texture of a soil sample, find its percent

Soil Textures � To determine the texture of a soil sample, find its percent for sand, silt, and clay. � The texture of the soil will be where all three lines intersect.

Soil Fertility �A measure of how well a soil can support plant growth �Factors

Soil Fertility �A measure of how well a soil can support plant growth �Factors involved include: • • • Availability of nutrients/minerals Precipitation Topography Acidity Number of microorganisms present

Soil Color �Factors that determine soil color include: • Climate • Soil’s composition �Topsoil-usually

Soil Color �Factors that determine soil color include: • Climate • Soil’s composition �Topsoil-usually dark (rich in humus) �Red/yellow soils-caused by iron minerals oxidizing �Yellow soils are often poorly drained, associated with environmental problems �Gray/bluish soils-poorly drained, constantly wet, lacking in oxygen