Soil

Mixture of geologic and organic materials. Needed for plant growth,

water filtration, habitat, biogeochemical cycles.

Topsoil- porous mixture of humus +org matter.

Leaf litter, partially decomposed leaves, twigs, animal waste fungi.

Subsoil – most of soil’s inorganicmaterial, clay, sand, gravel

Parent material – Broken rock that lays ontop of bedrock

Eluviation layer- only in acidic soilswith leaching Fe, Al, and acid rich

Things to know about soil horizons

• If the top soil is darker brown/black it means there is lots of organic matter and nitrogen.

• If the top soil is gray/yellow it is nitrogen poor with little organic matter.

• Layer O + A is the location of most plants and organic material. Also location of fungi, bacteria, and worms.

Not all soil is created equal and is dependent on

1. Parent material– CaCO3 will have high

pH and good for agriculture

– SiO2 or quarts will be nutrient poor

2. Climate– Ideally warm locations

with moderate precipitation and decomposition = lots of organic matter

– Equatorial regions = rapid rainfall, decomposition and weathering = leeching of nutrients.

3. Topography– Slope or outlay of the

land

4. Organisms– Plants

• hold soil in place• Add nutrients

– Animals• Aerate soil

– Humans • Compact soil• Deforestation• Permeability change

Physical Properties of soil

• Soil Texture– % sand, silt, clay in a soil

– Sand is > 0.05mm– Silt is between

0.05 and 0.002mm– Clay is <0.002mm

Soil Triangle

• Porosity– The percentage of open space in a material

compared to its total volume.• Shape –rounded particles have more porosity than

angular particles• Packing-closely packed particle have lower porosity• Sorting – sorted (same size) particle have higher

porosity than unsorted (variety of sizes)

Permeability:

• Ability for water to pass through and drain – Permeable: water passes through fast• gravel and sand have larger pore sizes but lower

porosity

– Impermeable: water passes through very slowly• silt and clay have high pore space but doesn’t allow for

water to move through it because of pore size

Permeability animation

Gravel and Sand: High porosity, high permeabilityBecause there are larger spaces between the pieces of gravel and grains of sand where water can go through easily.

Silt and Clay: Low porosity, low permeabilitySilt and clay are tightly packed together and have very small spaces between them.

Why did the water pass through the gravel and sand faster?

What is the relationship between sediment size and permeability?

• The larger the sediment, the more permeable because the spaces will be bigger.

• The smaller the sediment, the less permeable because the spaces will be smaller.

Porosity: