Soil

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

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

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:

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

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

gain.

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

Pollutants

Pesticides

Excess Fertilizer

Organic Pollutants VOCs, Semi-VOCs,

PCBs, PAHs, petroleum, solvents, organotin compounds

Heavy metals

Sources: Agrichemicals

Household cleaners

Gasoline, oil

Dry cleaning

Paints

Sludge

Landfills

Etc (see pg 458 in IB bk)

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

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.