Why is soil important?

1
Why is soil important?

• Nutrient cycling soil controls the release and
  uptake of nutrients (soil can trap carbon
  reducing greenhouse gas)
• Water relations Soil acts as a filter to protect
  the quality of water and air
• Biodiversity and habitat soil supports the
  growth of a variety of plants, animals and
  microorganisms ( The soil is an ecosystem)
• Physical stability and support Soil allows plant
  roots to anchor in the ground and structural
  support for buildings, roads and parking.

2
How does soil form?

• Soil erodes from parent material (rock) 1cm in
  250 -2,500 years

3
Weathering

• Physical/mechanical wind and rain, temperature
  change
• Chemical accelerated by warm wet conditions
  (acid rain)
• Biological lichens, tree roots

4
Biological activity

• Detritivores and decomposers cycle nutrients and
  produce organic matter (humus)
• Humus rich soils hold water and are nutrient rich

5
What lives in the soil?

• Each shovel of soil holds more living things than
  all the human beings ever born!
• We know more about the movement of celestial
  bodies than about the soil underfoot. ---
  Leonardo daVinci
• Yet, every plant and animal depends on this vast
  ecosystem

6
Worms!

• Up to 1, 750, 000 per acre in good agricultural
  soil!
• The weight of worms might outweigh the weight of
  livestock on a farm!
• Worms break down plant material into nutrient
  rich humus
• Burrowing improves soil structure for plant
  growth
• Earthworms aerate the soil
• Earthworms bring minerals from lower levels to
  the plant root zone

7
The soil profile

• Soil forms distinct layers called horizons
• Soil scientists classify soils according to their
  profiles
• O organic matter/litter
• A topsoil with organic and mineral content
• E zone of leaching
• B subsoil (minerals accumulate
• C weathered parent material
• R parent material

8
Alfisol
Andisol
9
oxisol
Vertisol
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Iowa - Mollisols

• Soils of grassland ecosystems
• Fertile surface horizon formed from long term
  addition of plant material
• Most widespread soil order in the U.S.
• Among the most productive agricultural soils of
  the world

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What is soil made of?

• 45 minerals
• 25 air
• 25 water
• 5 organic matter
• To describe soil we consider
• Color
• Structure
• texture

Soil texture classification
Particle type Size (mm)
clay 0.002
silt 0.002-0.05
sand 0.05-2.0
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Importance of Soil Texture

• Determines soils workability
• Porosity the size of the spaces between
  particles
• Fine particles have few spaces between them
  water and air move slowly
• Large particles water travels too fast
• Silty soil with medium pores OR loamy soils are
  favored by farmers

13
Which has the most fertile soil?
Temperate Grassland
Tropical Rainforest
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Soil Degradation and Conservation

• Erosion the removal of material (by wind or
  water) and its deposition at a new location
• 3 widespread practices lead to erosion
• Overcultivation
• Overgrazing
• Clearing forest on slopes

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Desertification

• A loss of more than 10 productivity due to
  erosion, soil compaction, forest removal,
  overgrazing, drought etc.
• Affects 1/3 of the planets land
• Could result in the displacement of 50M people in
  10 years

• 1930s dustbowl caused by drought, strong winds
  and poor farming practices

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Soil Conservation

• Crop Rotation
• Cover cropping (Rye)
• Contour Farming
• Terracing
• No-till or reduced tillage
• Shelterbelts (rows of trees)

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Salinization

• Irrigation may lead to a buildup of salts in
  surface soil
• Water evaporating from the A horizon may pull
  water from lower in the soil
• When water evaporates it leaves behind salts

• Overhead Irrigation

Drip Irrigation
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Overgrazing A tragedy of the Commons

• Too many animals eating too much ground cover
  leads to
• Erosion
• Soil compaction
• Invasive species (often less palatable to
  livestock

Degraded dryland in Greece