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 Sources: 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 Acid Rain and Storm water runoff
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.
Smith, T. M., and R. L. Smith Elements of Ecology, 7th edition. Benjamin Cummings.