Soil

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Soil
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Soil Formation

• The four major components of soil are
• Water (25)
• Air (25)
• Organic matter (6)
• Parent material (44)
• 2. Parent material is
• Bedrock which provides mineral content of
  the soil, Ex
• Sand, silt and clay
• Quartz SiO2
• Calcite CaCO3
• Feldspar KAlSi3O8
• Mica (biotite) K(Mg,Fe)3AlSi3O10(OH)2

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• 3. How is soil made from parent material? Include
  the role of weathering and living organisms
• Weathering (physical and chemical) creates small
  pieces
• Dead organisms- decay and release nutrients and
  gases
• living organisms also release nutrients and gases
• Parent material can be native to the area or
  transported to the area by wind, water or a
  glacier
• EX
• Calcareous soils in Miami-Dade County are derived
  from Miami limestone. Most of Miami-Dade County,
  part of Broward County, and Monroe County
  (including the Florida Keys). Broward also has
  marl and stone sand bedrock

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• 4. Humus is Organic matter
• Dead and decayed organisms, ex plant matter
• How long does it take to make soil from bare
  rock?
• 10 000 years

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• Soil Profile
• 1. Describe the 5 Soil horizons
• O- Organic matter, leaf litter (duff),
• dead animals, decomposed litter
• A- Surface soil, decomposed organic
• matter and minerals, humus (fertile)
• B- Subsoil, leached nutrients
  
• C- Parent rock, weathered large
• unbroken rocks
• R (Bedrock)- mostly a continuous
• mass of hard rock

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Soil Texture1. What is soil texture?

• Proportions of clay, sand and silt
• Particle size
• Smallest - clay less than .002mm
• - - Silt .002mm - .05mm
• largest - sand .05mm - 2 mm

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• 2. What is porosity?
•  Ability to hold water
• 3.What is permeability?
•  Ability of water to flow through the material
  (rate)
• 4. Compare permeability of sand and clay.
• Sand high, clay low

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• 5. What is a loam?
• A loam has about mixtures of clay, sand, silt
• and humus - best for growing crops.
• 6. How can soil texture be determined?
• Determined by particle size and feel

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• Soil type
• 1. What are the main Soil types?
• There are six main types of soil usually
  discussed in agriculture, distinguished by the
  size of the particle matter that makes up the
  soil.
• Sandy (water/minerals easily flow)
• Clay (no drainage)
• Silty (fertile, good drainage)
• Loamy (a mixture of soils)
• Chalky (alkaline)
• Peaty (acidic , undecomposed organic matter)

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Table 10-1 p. 216
Texture Nutrient Infiltration Water-Holding Aerati
on Tilth Capacity Capacity Clay Good Poor Good
Poor Poor Silt Medium Medium Medium Medium Medium
Sand Poor Good Poor Good Good Loam
Medium Medium Medium Medium Medium
Refer to Fig. 10-15 p. 215
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• Soil Erosion is the process by which soil and
  rock are removed from the Earth's surface by wind
  or water flow, and transported and deposited in
  other locations.
• Sheet erosion - surface water peels off fairly
  uniform sheets of soil.
• Rill erosion - fast flowing rivulets cut
• Small channels in soil.
• Gully erosion - rivulets join together to
• Cut wider, deeper ditches or gullies
• Two major impacts- loss of soil fertility and
  pollution of near by waters

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Causes of soil Degradation

• Deforestation
• No vegetation to hold the soil, soil is removed,
  loss of soil fertility, pollutes and can silt up
  rivers, decline in fish, flooding can worsen
• Management prevent deforestation, manage forest
  harvesting, replant

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Stepped Art
Fig. 10-6a, p. 219
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• 2. Agriculture
• Overgrazing- livestock are grazed on land in an
  unsustainable way (poorly managed) which leads to
  soil erosion and compaction of soil (due to the
  feet of the animals)
• Solutions-Rotational grazing- land is not grazed
  on until the plants have had enough time to grow
  back, cattle supplied with other food sources, ex
  hay
• Over grazing can lead to desertification

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Soils Degradation

• Desertification - combination of
• Prolonged drought and human activities
• Lead to a reduction in the productive
• potential of land.

• Solutions Reduce
• Overgrazing
• Deforestation
• Destructive forms of farming, irrigation, and
  mining

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Soils Degradation

• Salinization - salts left on soil as
• irrigation water evaporates. Stunts crop
• growth and reduces crop yields.

• Waterlogging - farmers leach salts from
• Soils by applying large amounts of water.
• if water does not drain, saline water sits in
  pools and damages roots of plants.
• Solution- Drip irrigation, better drainage

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Prevention
Cleanup
Reduce irrigation Switch to salt- tolerant
crops (such as barley, cotton, sugar beet)
Flushing soil (expensive and wastes water) Not
growing crops for 2-5 years Installing under-
ground drainage systems (expensive)
Preventing and cleaning up soil salinization
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Industrialized Crop Production Causes Soil Erosion

• Industrialized agriculture, high-input
  agriculture (intensive) produces 80 of worlds
  food supply
• Uses heavy equipment and large amounts of fossil
  fuels, water, commercial fertilizers, pesticides,
  and financial capital.
• Primarily monocultures single crop in one area.
• Goal is to steadily increase crop yield, Ex Corn

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Reduce Soil Erosion Due to Agriculture

• Soil conservation methods
• Crop rotation- Crop rotation is the practice of
  planting different crops during consecutive
  growing seasons.  By doing this the following
  benefits are applied to the soil and plants
• Strip cropping with cover crop

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Terracing Carving steep hills into terraces to
retain water at each level and prevent soil
erosion from downhill runoff. Contour farming
plowing rows to follow the curve of gently
sloping land. Same benefits as terracing.
Terracing
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Alley cropping rows of crops are planted
between a row of trees that provide fruit or
fuelwood and reduce Evaporation and wind blown
soil erosion Windbreaks - use rows of trees to
reduce wind erosion and help retain soil
moisture.
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Soil Degradation conventional tillage

• Conventional-tillage - fields often
• Plowed in the fall and left bare over
• winter. This leaves it vulnerable to
• Erosion, breaks soil structure
• Solution Conservation tillage
• Idea is to disturb the soil as little as
  possible when
• planting crops
• No-tillage- leave last years crop, use
• Seed injectors
• Minimum tillage - subsurface soil is
• loosened but not topsoil.

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CONSERVATON TILLAGE
Disadvantages
Advantages
Reduces erosion Saves fuel Cuts costs Holds
more soil water Reduces soil compaction Allows
several crops per season Does not reduce crop
yields
Can increase herbicide use for some
crops Leaves stalks that can harbor crop pests
and fungal diseases and increase pesticide
use Requires investment in expensive equipment
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• Water ManagementOver-watering a crop area will
  result in erosion of soil and possible flooded
  fields.  
• To counteract this farmers can plant crops native
  to the area that do not require external
  irrigation or employ minimal water techniques,
  such as drip-irrigation - the process of only
  watering  the crops themselves by using a hose
  with small holes at each crop.  

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• Case Studies
• MEDC- USA pg 303 textbook (Dustbowel 1930s)
• LEDC- India see article

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• Types of Soil
• Podzols are soils with an ash-grey subsurface
  horizon, bleached by organic acids, on top of a
  dark accumulation horizon with brown or black
  reddish iron compounds.
• Podzols occur in the Boreal and Temperate Zones
• Soils are acidic (pine needles), little ground
  vegetation
• Sandy not good for farming

• Characteristics
• Cool moist environment
• Climate
• Evergreen so limited litter layer
• Slow to decompose due to limited soil organisms
  (cold)
• Water
• Lots of water, snow melt
• Water infiltrates through layers, leaches out
  nutrients (Fe, Al) that collect lower down the
  profile.

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• Soil horizons

• Soil profile

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