Soil Composition – What Dirt is Made of Rock particles Minerals Dead, decaying plant and animal material (humus) Bacteria, fungi and other microbes Worms

Soil Composition – What Dirt is Made of

Rock particlesMineralsDead, decaying plant and animal material (humus)Bacteria, fungi and other microbesWorms and insectsAirWater

1. Why is Dirt Important?

Soil contains the minerals and nutrients that plants need to grow.

Soil provides shelter for plants and animals.

Soil absorbs, stores, and filters water.

Profile = Layer of soil also called horizon.

Litter (hummus) – dead leaves, grass, and waste material

A. Topsoil – rock pieces, nutrients, water, air and decaying matter (most animals live here)

B. Subsoil – rock fragments, water and air. (less plant/animal matter)

D. Bedrock – rock that makes up Earth’s crust.

Example Sizes:

1. US Department of Agriculture (USDA) which defines the size of:


Particle size affects:

PERMEABILITY.How freely water can flow/move

through soil is called

AS soil particle size increases, water flow increases meaning that permeability increases. High permeability means soil CAN’T hold moisture.



Soil Texture -

A way of classifying soil that depends on particle size.

Examples: loam, sand, clay, silt

Most plants grow best in loam soil = sand/silt/clay

Texture affects the amount of water a soil can hold.



Packed soil, like red clay, does not let water move through very easily.

One grain of clay is SUPER small.

Loose soil, like gravel, lets water pass through very easily.

– One grain of gravel is a BIG rock.



pH of Soil -

Soils can be basic or acidic.

Most plants grow best in soils with a pH between 5-7

If soil is too acidic, lime can be added to make it more basic.



Soil Formation: Soil forms as rock is broken down by weathering and then mixes with other materials on the surface of Earth’s crust.

Types of weathering: heat, cold, water (rain) and yes, air (O2 and CO2).

How do rocks break into smaller pieces?

Freezing and thawing breaks apart bedrock

Plant roots wedge between rocks and break them

Acid rain/chemicals break down rocks Animals help grind rock into smaller

pieces. Break down of dead organisms add to

the mixture.

Nutrient Depletion: Soil becomes less fertile – If farmers replant crops over and

over with out fertilizing soil, the crops use nutrients faster than decomposers can supply.

Erosion:

Movement of rock and soil by wind, water and gravity.

Are all soils the same?

Soil type affects which type of plants/animals can live there.

Factors that affect soil type are:Types of plants Climate TimeSlope of the land

Documents

Soil Composition – What Dirt is Made of Rock particles Minerals Dead, decaying plant and animal material (humus) Bacteria, fungi and other microbes Worms