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 • Affects Structure • 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. Sources: Agrichemicals Household cleaners Gasoline, oil Dry cleaning Paints Sludge Landfills Etc (see pg 458 in IB bk) Pollutants • Pesticides • Excess Fertilizer • Organic Pollutants • VOCs, Semi-VOCs, PCBs, PAHs, petroleum, solvents, organotin compounds • Heavy metals

12. Soil Degradation • Salinization • Water used for irrigation leaves behind salts • Too much salt and plant life cannot survive • Water tables rise, more evaporation occurs since surface is warmer so salinization occurs • Water table rose because land was cleared of trees • When it rained the trees held a lot of the moisture • Without the trees, the water seeps into the groundwater and becomes part of it. The water table rises. • The salty water of the water table mixes with the rain water... • 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.