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 inorganic material, clay, sand, gravel Parent material – Broken rock that lays on top of bedrock Eluviation layer- only in acidic soils with 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 – CaCO 3 will have high pH and good for agriculture – SiO 2 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 PermeabilityPermeability animation

Gravel and Sand: High porosity, high permeability Because 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 permeability Silt 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: