Soils

SoilsSoils

What is soil?What is soil?

• Thin layer on the earth’s surface that is made by the interaction of five factors: rocks, sunlight, water, air, and living organisms

Soil CompositionSoil Composition The average soil is mainly composed of

mineral particles that come from rocks. Below is the composition of an average soil.

Taken from http://www.physicalgeography.net/fundamentals/10t.html

Soil Formation/CompositionSoil Formation/Composition

• The formation of 1 meter of soil can take from 100 – 100,000 years to form (depending on the conditions present)

• Climate affects rate• Higher temp. and more rain = faster soil

formation• Rain provides water for chemical reactions

to occur and warmer temp. increases speed of reactions

Soil formation/CompositionSoil formation/Composition

• Rocks are the “parents” of the soil

• Parent material affects the kind of soil that is formed

• Different rocks contain different minerals

• Color of soils is partially dependent on the minerals the soils contain

Soil formation/CompositionSoil formation/Composition

• Weathering – the process of breaking rocks apart or removing minerals from them.

• Weathering agents can be physical and chemical

• Weathering agents include water, ice, wind, temperature changes, sand, glaciers, and plant roots

Soil formation/CompositionSoil formation/CompositionWeatheringWeathering

• Temp. changes cause rocks to expand and contract cracking rocks and releasing minerals

• Water in cracks can turn to ice further splitting rocks• Roots can act as physical wedges. They can also

produce chemicals that dissolve minerals from the rocks• Sand and rocks carried by moving water scour the soil

and rocks beneath• Glaciers that carry much bigger rocks can file and scrape

rocks below• Wind-blown sand acts like a sandblaster on the surfaces

of rocks

Soil formation/CompositionSoil formation/CompositionChemical Changes in RocksChemical Changes in Rocks

• Equation for ferric oxide reaction (rust)

Significance of reaction:

Soil formation/CompositionSoil formation/CompositionChemical Changes in RocksChemical Changes in Rocks

• Equations for Carbonic acid formation and calcium and bicarbonate ion formation:

• Significance of reactions:

Soil CompositionSoil Composition

• The average soil consists of 25% air and 25% water.

• Water and air are extremely important

-for plant roots

-for many of the bacteria, protists, fungi,

and animals that live in the soil

-All of the organisms that live in the soil interact

together to form the soil ecosystem

Soil CompositionSoil CompositionOrganic Matter Organic Matter

• An average soil contains 5% of organic matter

• Although organic matter is only a small percentage of the overall soil it is extremely important

• In an average soil, 80% of the organic matter is humus, 10 % is roots, and 10% is organisms

HumusHumus

• Humus-partly decomposed organic matter that was once living or was produced by a living thing.

• Provides nutrients to many organisms

• Increases water-holding capacity of soil

• Provides nutrients to plants

Image taken fromhttp://urbanext.illinois.edu/soil/SoilBiology/soil_food_web.htm

Taken from http://permaculturenews.org

Soil textureSoil texture

• Mineral particles in soil are classified by size

• Size of particles determines soil texture

• See soil texture chart on page 213

Soil TextureSoil Texture

Soil TriangleSoil Triangle

Spaces in soilSpaces in soil

• Normally 40-60% of volume of soil is pore space

• Important for water and air to travel through soil

• Determine infiltration and percolation rates

• Size of spaces is dependent on texture

• Smaller particles=smaller spaces

• Larger particles=larger spaces

Key termsKey terms

• Soil texture – size of mineral particles

• Infiltration – the ability of water to soak into the soil

• Water holding capacity – the ability of soil to store water

• Aeration – the ability of air to move through the soil

Soil ComparisonSoil Comparison

Soil Texture Infiltration Water-Holding Capacity Aeration

SAND Good Poor Good

SILT Medium Medium Medium

CLAY Poor Good Poor

LOAM Medium Medium Medium

*Loam is considered an ideal soil for many crops due to its mix of different soil particles (sand, silt, and clay)

Soil StructureSoil Structure

• Structure-when individual particles are “glued” together to form larger pieces

• The “glue” is produced by organisms in the soil

• Granular structure-rounded clumps with a diameter of less than 1.5 cm

• Crumb structure-irregular shaped clumps• Platy structure-soil particles glued together

into thin horizontal plates

Soil Profile (in descending order)Soil Profile (in descending order)

• Topsoil-top layer of humus rich soil

• Subsoil-layer of soil beneath the topsoil (does not contain humus)

• Parent material –the pieces of rock that lie on top of solid rock

• Bedrock-solid rock

Soil ConservationSoil Conservation

• Erosion-the process in which wind or water move soil to new locations

• Erosion occurs naturally but can also be caused by human activities

• To much erosion is bad for farming

• Displaced soil can also be a major pollutant of aquatic ecosystems

Some causes of erosionSome causes of erosion

• Overgrazing by livestock

• Repeated years of monocultures

• Plowing land

• Construction

• Surface mining

• logging

Preventing erosionPreventing erosion

• Contour planting-planting across a slope (rather than up and down it)

• Strip cropping-strips of close growing plants are planted next to crops that are planted in rows

• Diversion terraces-ridges of soil that are constructed along the contours

• Waterways-wide ditches that are planted with a permanent grass cover

Contour plantingContour planting

http://www.extension.iastate.edu/agdm/crops/html/images/a1-41/image5.jpeg

Strip CroppingStrip Cropping

http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1088801071&topicorder=12&maxto=16

Diversion TerracesDiversion Terraces

http://www.wi.nrcs.usda.gov/programs/solutions/diversion.html

WaterwaysWaterways

http://milford.nserl.purdue.edu/weppdocs/overview/practices.html

Preventing erosionPreventing erosion

• Crop rotation

• Windbreaks

• Conservation tillage-methods to reducing the amount of tilling and avoid the use of the moldboard plow

• Cover crops-grasses or legumes planted to hold soil in place

Crop RotationCrop Rotation

http://www.marionswcd.net/crop-rotation/

WindbreaksWindbreaks

http://www.mda.state.mn.us/protecting/conservation/practices/fieldwindbreak.aspx

Conservation TillageConservation Tillage

http://nfrec.ifas.ufl.edu/programs/impacts_conservation_tillage.shtml

Cover CropsCover Crops

http://biocontrol.ucr.edu/irvin/research/wsare.html

The dust bowlThe dust bowl

• Dust bowl- Area in the southern part of the great plains which experienced massive amounts of soil erosion during the 1930s

• Caused by poor farming practices combined with drought and winds

• As a response the federal government created several agencies and policies to prevent soil erosion