soil. what is soil? mixture of inorganic material (rocks) and organic material (som) as well as...
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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?
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
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
Structure of Soil: Inorganic
Silicon is to geologists what carbon is to biologists...
Rocks and soils basic structure:
- 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
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
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
Soil Ecosystem: Detrital Food Chain
Soil Organic Matter: Possible Structure
Polar parts Hold water
Hold inorganic nutrients (ions: nitrate, phosphate)
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
Organic Pollutants VOCs, Semi-VOCs,
PCBs, PAHs, petroleum, solvents, organotin compounds
Etc (see pg 458 in IB bk)
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
Green J., Damji S. Chemistry 3rd Ed. IBID Press, 2007.
Smith, T. M., and R. L. Smith. 2009. Elements of Ecology, 7th edition. Benjamin Cummings.