HOW DOES SOIL FORM?GLOBE NY Metro, 2008

White, 2014

Soil is:

the naturally occurring, unconsolidated or loose covering of broken rock particles and decaying organic matter on Earth’s surface, capable of supporting life.

Soil has three components: solid, liquid, and gas.

The solid phase is a mixture of typically loosely-packed mineral and organic matter particles forming a soil structure filled with voids.

The void space contains water (liquid) and air (gas).

Soil is also known as earth: it is the substance from which our planet takes its name.

Soil is a portion of the regolith, the mantle of loose, heterogeneous material that rests on solid bedrock.

Regolith includes saprolite or weathered bedrock typically considered to be the lowermostportion of a soil profile.

Why is soil important?

Soil formation, or pedogenesis, is controlled by five variables in nature,

the so-called state factors:

1. parent material2. climate3. topography4. biota5. time6. humans

Parent material: residual -v- transported

Parent material: Chemical changes during soil formation depend on what minerals and rocks are present. Example: Calcium-rich soils generally form from calcium-rich rocks (like limestone) but not from calcium-poor rocks like granite.

Climate: temperature and precipitation

Climate: heat and water accelerate chemical changes (so moist, temperate areas like NYC have different soils than arid, tropical, or polar areas).

Topography:elevation,slope,aspect

Topography: Loose soil stays in place in flat areas, allowing more thorough physical and chemical alteration of its grains. On steep slopes, the soil moves downhill before complete alteration can occur.

Biota:organisms

Living things: Plant roots physically break rocks into small pieces; lichen dissolves rock; burrowing animals mix the soil and help aeration

Biota:ecosystem

Time

TIME: When bedrock is exposed at the surface, chemical, biologic, and physical processes combine to produce a thin soil layer. Over time, the processes extend vertically downward, developing soil horizons whose position and thickness change over time.

State factor interaction: e.g. topography/parent material

Soils are characterized in the field in natural exposures, dug soil pits, or using augers to bore holes and obtain samples from the subsurface.

White, 2014

5 FACTORS CONTROL THE TYPE OF SOIL

TIME is the 5th factor Soil forms by the interaction of the first four factors. It changes to create soil profiles unique for the conditions and elapsed time. A soil profile consist of layers called “soil horizons”

Photo courtesy, Ray Weil, PhD

Parent Material

Topography

Climate

Living things

4 factors control soil-

forming processes

If all five factors are the same in two geographic regions, the soil will be the same in both. Some basic examples of

different soil types include:

Temperate deciduous soil Coniferous forest soil Grassland soilConiferous forest soil

Tropical rain forest soil Desert soil

United States Department of Agriculture

Soils are very different, depending on how they form

Why do we study soil? Because It’s A(n)

Great integrator

Producer andabsorber of gases (CO2 and others)

Medium for plant growth

Medium of crop production

Home to organisms(plants, animals and others)

Waste decomposer

Snapshot of geologic, climatic, biological, and human history

Source material for construction, medicine, art, etc.

Filter of water and wastesEssential natural resource

Medium of heat andwater storage

Soil is an excellent place to study interactions in the Earth System, including contributions from the

Atmosphere• Dew (moisture from the air) begins chemical alteration of parent rock • Rain erodes loose soil, preventing further alteration • temperature controls rate and extent of chemical processes

Hydrosphere• Water seeps into the ground, dissolving and redistributing elements• evaporation dries soil, changing its physical characteristics

Biosphere• plants add and remove chemicals • plant roots anchor soil in place, enabling chemical reactions to be completed • animals mix soil; transport seeds, etc.

Geosphere• solid rock and unconsolidated sediment are the parent material for soil • geologic processes (surface and internal) expose and bury rock, etc.

Hydrologic Cycle and the Soil

Color

Structure

Bulk Density

Texture

pH

Temperature

Soil moisture

HorizonDepths

Soil Properties related to the hydrologic cycle.

Review: ROLES OF THE FIVE FACTORS OF SOIL FORMATION

Living things: Plant roots physically break rocks into small pieces; lichen dissolves rock; burrowing animals mix the soil and help aeration

TIME: When bedrock is exposed at the surface, chemical, biologic, and physical processes combine to produce a thin soil layer. Over time, the processes extend vertically downward, developing soil horizons whose position and thickness change over time.

Parent material: Chemical changes during soil formation depend on what minerals and rocks are present. Example: Calcium-rich soils generally form from calcium-rich rocks (like limestone) but not from calcium-poor rocks like granite.

Topography: Loose soil stays in place in flat areas, allowing more thorough physical and chemical alteration of its grains. On steep slopes, the soil moves downhill before complete alteration can occur.

Climate: heat and water accelerate chemical changes (so moist, temperate areas like NYC have different soils than arid, tropical, or polar areas).