Soil

1
Soil
2
What is soil?

• Mixture of inorganic material (rocks) and organic
  material (SOM) as well as organisms (microbes).
• Soil formation involves
• Parent Material (glacial deposits? Sediment?
  Lava?)
• Biotic Factors
• Plant roots break up soil, add nutrients and
  organic material
• Climate influences
• Temp, precipitation, wind leaching movement
  solute thru soil
• Topography
• More water flow? Steep slopes?
• Time

3
Characteristics of Soil

• Color
• Dark humus, other colors minerals present
• Texture
• Gravel, sand, silt, clay
• Structure
• moisture, air capacity and ion exchange ability
• Moisture
• Wet soils vs dry soils support different forms of
  life
• Depth

4
What role does soil serve in the ecosystem?

• Part of both food webs
• Provides nutrients for plants
• Plants are a sink for toxic metals, organic
  toxins, carbon
• Plants are a food source
• Plants prevent erosion
• Detritovores recycle nutrients so they can be
  used by other organisms
• Turn Nitrogen into nitrates
• Recycle the nitrogen and carbon out of dead
  things (mineralization)
• Eat up pollutants
• Holds moisture/ filters water

5
Structure of Soil Inorganic

• Silicon is to geologists what carbon is to
  biologists...
• Rocks and soils basic structure
• Silica SiO2
• Aluminosilicate
• AlSi3O8- or AlSi3O8-
• Negative charge allows soil to hold on to
  important mineral cations Ca2, K, Na, Mg2,
  NH4,

Al3 can be substituted for Si4 1 in 4 will
give a -1 charge 2 in 4 gives a -2 charge
6
Soil Organic Matter

• Non-living organic components present in soil
  resulting from decomposition of once living
  creatures
• Holds onto nutrients to exchange with plants
• Improves soil structure
• Increase air
• More oxygen,
• Easier for roots to grow
• Increased moisture
• Heat capacity / smaller temperature deviations
• Reduces soil erosion

7
Soil Organic Matter

• The organic material from bacterial breakdown of
  plants and other organisms
• Nature's way of recycling important nutrients
• Sugars, amino acids, proteins, polysaccharides
• Humic acids (Hummus)
• Still don't really know what it is
• Stable organic material that isn't broken down
  any more by organisms.
• Organisms will only eat what will give them a
  net energy gain.

8
Soil Ecosystem Detrital Food Chain
9
Soil Organic Matter Possible Structure

• Polar parts
• Hold water
• Hold inorganic nutrients (ions nitrate,
  phosphate)

10
Importance of Soil Organic Matter

• SOM gives the soil better Structure
• More moisture, more oxygen can diffuse, more
  pockets for microorganisms to live
• Better soil structure supports more
  microorganisms
• Microorganisms mineralize nutrients
• Amino acids ? Nitrates ? Natural fertilizer for
  plants
• Using compost is a way to increase soil organic
  matter into bad soil

11
Pollutants

• Pesticides
• Excess Fertilizer
• Organic Pollutants
• VOCs, Semi-VOCs, PCBs, PAHs, petroleum, solvents,
  organotin compounds
• Partition in SOM (humic substances)
• Adsorb to surface of inorganic soil
• Heavy metals

• Sources
• Agrichemicals
• Household cleaners
• Gasoline, oil
• Dry cleaning
• Paints
• Sludge
• Landfills
• Etc (see pg 458 in IB bk)

12
Soil Degradation

• Salinization
• Water used for irrigation leaves behind salts
• Too much salt and plant life cannot survive
• Water tables rise (due to deforestation), more
  evaporation occurs since surface is warmer so
  salinization occurs
• Acid Rain and Storm water runoff
• Leaching of important nutrients for plants

13
Sources

• Green J., Damji S. Chemistry 3rd Ed. IBID Press,
  2007.
• http//www.science.org.au/nova/032/032box01.htm
• Smith, T. M., and R. L. Smith. 2009. Elements of
  Ecology, 7th edition. Benjamin Cummings.