The Dirt on

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The Dirt on Soil
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Ecological definition of Soil
Soil a mixture of mineral particles, organic
matter, water, and air and is capable of
supporting life.
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Soil Components

• Abiotic (non living parts)
• Mineral matter
• Pore space for air and water
• Source of plant nutrients
• Si(silicon), Al(aluminum) and Fe(iron) oxides
  (90).

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Soil Components

• Biotic (living parts)
• Dead and decaying matter (humus)
• Source and exchange for nutrient cycling.
• Bacteria (1000g/m2)
• Earthworms (120 g/m2)

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Soil Components
Water

• Solvent for many essential plant nutrients.

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Air Component

• Oxygen -- for respiration of plant roots and soil
  organisms.
• CO2 --from soil respiration
• N2 --(nitrogen gas) for N-fixing soil
  organisms.

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Formation of Soil

• Can take thousands of years or more.
• Formed from the weathering of rocks and
  minerals
• The surface rocks break down into smaller pieces.
  (weathering)
• They get mixed with moss and organic matter
  creating a thin layer of soil (erosion)
• Plants then attract animals whose bodies decay
  after they die. This decaying matter makes the
  soil thick and rich with nutrients.
  (humification)
• Minerals come from Bacteria in the soil.

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Soil Organization
A Horizon or topsoil - highly weathered  -
abundant life, therefore, high in organic   
matter - dark colored  B Horizon or
subsoil -less weathered, more clay -less life,
low organic matter -lighter colored C horizon or
parent material -little weathered -little life,
except deep rooted plants -little to no organic
matter D Horizon or bedrock -rock base
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who cares about organic matter?
Functions of Organic Matter   1- stabilizes
soil structure  2- increases water retention and
availability  3- increases drainage and
aeration (air in soil) 4- supplies nutrients
upon decay 5- stabilizes pH  6- food source for
microorganisms 
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Types of Soil

• Classified by the amount of sand, silt, and clay.
• Sand Silt Clay

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Soils of Loudoun County
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Human Effects
Erosion It takes 1 year to form 5 tons of soil,
we lose 50 tons of soil per year due to erosion.
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• Caused by vegetation loss.
• Conventional tillage.
• Overgrazing.
• Development of land.

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Soil Erosion in Loudoun County

• One of the fastest growing counties in the
  nation.
• Sediment is 1 pollutant of surface water.
• Affects drinking water, promotes harmful
  vegetation and algae, clogs drainage systems.
• Construction sites have 200X faster erosion than
  cropland and 2,000x faster than woodland.

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Controling Erosion
A.) Create wind breaks using trees. B) Silt
Fencing, Erosion Controls grass planting B.)
Conservation Tillage/Plowing C.) Planting cover
crops D.) Terracing reducing water flow. E)
Contour Farming
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Real Examples
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Types of Contour Farming
Terraces
Buffer Strips
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• Desertification
• Conversion of rangeland to desert-like
  conditions.
• Caused by exceeding the carrying capacity through
  overgrazing.
• Soil becomes bald or bare and compacted
• Air heats the land and rainfall decreases.

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Dust Bowl of 1930s
Caused by drought and poor agricultural
practices. Wind erosion caused major soil loss
and dust storms. Responsible for lengthening the
Depression.
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Irrigation

• 1 use of fresh water
• Results in salinization
• Salts in water are deposited on the surface

Control by using drainage tile and drip
irrigation.
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Fertilizers and Pesticides

• Increases resistance of pests
• Decreases population of beneficial organisms
• Causes eutrophication
• Causes water pollution

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Types of Pesticides
Chemical Pesticides
Chemical Pesticides -Most affect the nervous
system and can also be toxic to humans. Some were
used in WWII as nerve agents. Ex. DDT
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DDT

• The First Chlorinated pesticide
• VERY effective against mosquitos that spread
  malaria
• Insects began to develop resistance due to
  over-use
• Very toxic to Fish and birds (thins egg shells)
• Caused cancer in humans with high exposure
• Takes 8 years for an animal to get rid of DDT
  from its system
• Banned in 1973

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Types of Pesticides Contd
Biopesticides -Made from natural elements like
animals, plants, or bacteria. Ex Canola oil and
Baking soda -Sometimes involves using natural
enemies of pests to eliminate them from the
crop. Ex ladybug larvae eat aphids,
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Controls for Pesticides and Fertilizers
Use crop rotation Use compost and/or Green manure
(fungus that lives on roots and absorbs excess
nitrogen)
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Homework!!

• Research and List at least 5 ways to control
  pests WITHOUT using chemical pesticides.
• You can type OR handwrite the 5 ways.
• You can use any sources (internet, books,
  encyclopedias, etc)

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Pfiesteria Outbreak in VA/MD
In 1997 several tributaries to the Chesapeake Bay
experienced fish kills due to a toxic organism
Pfiesteria piscicida.

Pfiesteria blooms are caused by excess nitrogen
from poultry manure being used as fertilizer on
cropland.
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Soil is one of our most valuable natural
resources and should be conserved and protected.