SOILS What is soil Soil relatively thin surface

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SOILS

SOILS

What is soil? • Soil – relatively thin surface layer of the Earth’s crust

What is soil? • Soil – relatively thin surface layer of the Earth’s crust consisting of mineral and organic matter

Soil Composition • Soil is composed of 4 distinct parts: – Mineral particles (45%

Soil Composition • Soil is composed of 4 distinct parts: – Mineral particles (45% of “typical” soil) – Organic matter (about 5%) – Water (about 25%) – Air (about 25%)

Importance of Soil • Organisms inhabit the soil & depend on it for shelter,

Importance of Soil • Organisms inhabit the soil & depend on it for shelter, food, & water. • Plants anchor themselves into the soil, and get their nutrients and water. • Humans need plants and, therefore, need soil.

Soil is a renewable resource • Soil is a slowly renewed resource • Soil

Soil is a renewable resource • Soil is a slowly renewed resource • Soil formation begins when bedrock is broken down by weathering. • Mature soils (soils that have developed over a long time) are arranged in a series of horizontal layers called soil horizons.

Soil Formation • Soils form from parent material • Parent material (rock) is slowly

Soil Formation • Soils form from parent material • Parent material (rock) is slowly broken down into smaller particles by biological, chemical, and physical weathering. • It takes a long time to form soil. – Example: To form 2. 5 cm (1 in. ) it may take from 200 -1000 years.

Physical Weathering • Physical breakdown by wind, water, ice, etc.

Physical Weathering • Physical breakdown by wind, water, ice, etc.

Chemical Weathering • Chemicals interact with rock and break it down. • Example: A

Chemical Weathering • Chemicals interact with rock and break it down. • Example: A plant’s roots or animal cells undergo cell respiration and the CO 2 produced diffuses into soil, reacts with H 2 O & forms carbonic acid (H 2 CO 3). This eats parts of the rock away.

Biological Weathering • Parent material is broken down by tree roots or lichens. •

Biological Weathering • Parent material is broken down by tree roots or lichens. • Lichens play a big role in primary succession.

Soil Properties: Texture • The percentages (by weight) of different sized particles of sand,

Soil Properties: Texture • The percentages (by weight) of different sized particles of sand, silt and clay that it contains.

Soil Properties: Texture, Cont. • Grain Size – 0. 05 to 2 mm =

Soil Properties: Texture, Cont. • Grain Size – 0. 05 to 2 mm = sand (the largest soil particles) – 0. 002 to 0. 05 mm = silt (about the size of flour) – <. 002 mm = clay (only seen under and electronic microscope)

Soil Properties: Texture, Cont. • To tell the difference in soil, take the soil,

Soil Properties: Texture, Cont. • To tell the difference in soil, take the soil, moisten it, and rub it between your fingers and thumb. – Gritty: has a lot of sand – Sticky: high clay content and you should be able to roll it into a clump – Silt: smooth, like flour.

Soil Structure • How soil particles are organized and clumped together. – Sand –

Soil Structure • How soil particles are organized and clumped together. – Sand – Silt – Clay

Friability • How easily the soil can be crumbled.

Friability • How easily the soil can be crumbled.

Porosity • A measure of the volume of soil and the average distances between

Porosity • A measure of the volume of soil and the average distances between the spaces.

Permeability • The rate at which water and air moves from upper to lower

Permeability • The rate at which water and air moves from upper to lower soil layers. • The Distances between those spaces.

Variability • Soils (Sand, Silt, & Clay) vary in – the size of the

Variability • Soils (Sand, Silt, & Clay) vary in – the size of the particles they contain – the amount of space between these particles – how rapidly water flows through them.

Big spaces, not a lot of them LESS surface area AL U EQ SITY

Big spaces, not a lot of them LESS surface area AL U EQ SITY O R PO Little spaces but lots of them GREATER surface area IMPORTANT TO REMEMBER The size of the rock particle DOES NOT change the porosity!

1 st trial: look at red yellow green only Demo #1 Which size held

1 st trial: look at red yellow green only Demo #1 Which size held the most water?

Soil Texture (descriptions) • Sand • Silt • Clay

Soil Texture (descriptions) • Sand • Silt • Clay

Shrink-Swell Potential • Some soils, like clays, swell when water gets in them, then

Shrink-Swell Potential • Some soils, like clays, swell when water gets in them, then they dry and crack. This is bad for house foundations, etc.

Slope • Steep slopes often have little or no soil on them because of

Slope • Steep slopes often have little or no soil on them because of gravity. • Runoff from precipitation tends to erode the slope also. • Vegetation?

Depth • Some soils are very shallow. It can be only two inches of

Depth • Some soils are very shallow. It can be only two inches of soil and then you hit rock. Other areas can have soil 36 inches deep or more.

Color • Dark soil is rich with lots of organic matter. • Light soil

Color • Dark soil is rich with lots of organic matter. • Light soil (like sand) is not so rich with very little organic matter.

Soil Horizons

Soil Horizons

Organic Layer (O-horizon) • The uppermost layer; it is rich in organic material. •

Organic Layer (O-horizon) • The uppermost layer; it is rich in organic material. • Plant litter accumulates in the O-horizon and gradually decays. • In desert soils the O-horizon is completely absent • In certain rich soils it may be the dominant layer.

Topsoil (A-horizon) • It is dark and rich in accumulated organic matter and humus.

Topsoil (A-horizon) • It is dark and rich in accumulated organic matter and humus. • It has a granular texture and is somewhat nutrient-poor due to the loss of many nutrient minerals to deeper layers and by leaching.

Eluvial(E-horizon) • Mineral horizon in upper part of soil • Below A-Horizon and above

Eluvial(E-horizon) • Mineral horizon in upper part of soil • Below A-Horizon and above B-Horizon • Generally forested areas, light color

Subsoil (B-horizon) • The light-colored subsoil beneath the Ahorizon; • Accumulation of minerals occurs

Subsoil (B-horizon) • The light-colored subsoil beneath the Ahorizon; • Accumulation of minerals occurs here • It is typically rich in iron and aluminum compounds and clay.

Parent Material (C-horizon) • Contains weathered pieces of rock and borders the unweathered solid

Parent Material (C-horizon) • Contains weathered pieces of rock and borders the unweathered solid parent material. • Most roots do not go down this deep • often saturated with groundwater.

Oak tree Wood sorrel Lords and ladies Fern O horizon Leaf litter Dog violet

Oak tree Wood sorrel Lords and ladies Fern O horizon Leaf litter Dog violet Grasses and small shrubs Earthworm Millipede Honey fungus Mole Organic debris builds up Rock fragments Moss and lichen A horizon Topsoil B horizon Subsoil Bedrock Immature soil Regolith Young soil Pseudoscorpion Mite Nematode C horizon Parent material Root system Mature soil Red Earth Mite Springtail Actinomycetes Fungus Bacteria Fig. 3 -23, p. 68

Mosaic of closely packed pebbles, boulders Weak humusmineral mixture Desert Soil (hot, dry climate)

Mosaic of closely packed pebbles, boulders Weak humusmineral mixture Desert Soil (hot, dry climate) Dry, brown to reddish-brown with variable accumulations of clay, calcium and carbonate, and soluble salts Alkaline, dark, and rich in humus Clay, calcium compounds Grassland Soil (semiarid climate) Fig. 3 -24 a, p. 69

Acidic light-colored humus Iron and aluminum compounds mixed with clay Tropical Rain Forest Soil

Acidic light-colored humus Iron and aluminum compounds mixed with clay Tropical Rain Forest Soil (humid, tropical climate) Fig. 3 -24 b, p. 69

Forest litter leaf mold Humus-mineral mixture Light, grayishbrown, silt loam Dark brown firm clay

Forest litter leaf mold Humus-mineral mixture Light, grayishbrown, silt loam Dark brown firm clay Deciduous Forest Soil (humid, mild climate) Fig. 3 -24 b, p. 69

Acid litter and humus Light-colored and acidic Humus and iron and aluminum compounds Coniferous

Acid litter and humus Light-colored and acidic Humus and iron and aluminum compounds Coniferous Forest Soil (humid, cold climate) Fig. 3 -24 b, p. 69

Erosion • Erosion is the movement of soil components, especially surface litter and topsoil,

Erosion • Erosion is the movement of soil components, especially surface litter and topsoil, from one place to another.

Importance of Erosion • In undisturbed ecosystems, the roots of plants help anchor the

Importance of Erosion • In undisturbed ecosystems, the roots of plants help anchor the soil, and usually soil is not lost faster then it forms. • But, farming, logging, construction, overgrazing by livestock, off-road vehicles, deliberate burning of vegetation etc. destroy plant cover and leave soil vulnerable to erosion. This destroys in a few decades what nature took hundreds to thousands of years to produce.

Soil Erosion & Degradation Figure 13 -9

Soil Erosion & Degradation Figure 13 -9

Global Outlook: Soil Erosion • Soil is eroding faster than it is forming on

Global Outlook: Soil Erosion • Soil is eroding faster than it is forming on more than one-third of the world’s cropland. Figure 13 -10