SOIL

Soil is a natural body comprised of solids (minerals and organic matter), liquids, and gasses that form on the land surface, occupy space, and are characterized by one or both of the following:

- Horizons (or layers) that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter

-Or the ability to support rooted plants in a natural environment

1. Soil system storages include organic matter, organisms, nutrients, minerals, air, and water.

2. Transfers of material within the soil, including biological mixing and leaching (minerals dissolved in water moving through the soil), contribute to the organization of the soil.

3. Organic material inputs include leaf litter and inorganic matter from parent material, precipitation, and energy. Outputs include uptake by plants and soil erosion.

4. Transformations include decomposition, weathering, and nutrient cycling.

5. The structure and properties of sand, clay, and loam soils greatly differ. Mineral and nutrient content, drainage, water-holding capacity, air spaces, biota, and potential to hold organic matter are all linked to the ability of the soil to promote primary productivity.

6. The upper limit of soil is the boundary between soil and air, shallow water, live plants, or plant materials that have not begun to decompose. Areas are not considered to have soil if the surface is permanently covered by water too deep (typically more than 2.5 meters) for the growth of rooted plants.

7. The lower boundary that separates soil from the non soil underneath is the most difficult to define. Soil consists of horizons near the Earth's surface that, in contrast to the underlying parent material, have been altered by the interactions of climate, relief, and living organisms over time.

Inorganic Components

• Rock fragments

• Sand

• Silt

• Clay

Organic Components

Living Organisms:

• Bacteria

• Fungi

• Earthworms

Dead organic matter:

• Decaying plants

• Animal remains

• Animal waste (feces)

Soils as Systems

• Soils are dynamic systems within larger ecosystems

• As with any system, soil systems can be simplified by breaking them into the following components:

• Storages

• Flows (input and outputs)

• Transfers (change in location) and transformations (change in chemical nature, state or energy).

Soil Profiles

• Soil profiles develop as a result of long-term interactions within the soil system

• These interactions and processes form distinct layers known as horizons

• These layers vary in composition and characteristics from the surface downward

• This reflects the process of soil formation over time

• Profiles usually transition from organic-rich layers near the surface to more mineral-rich layers deeper down

• These lower layers generally contain more inorganic material

• The development of soil profiles are influenced by factors such as:

• Climate

• Vegetation

• Parent material

• Time

Real-World Examples

• Tropical rainforests:

• Often have thick, organic-rich top soils due to rapid decomposition and high biological activity

• Desert regions:

• Characterized by shallow, mineral-dominated soils with distinct horizons due to low organic matter input and minimal leaching

• Peat soils in boreal forests:

• Soils characterized by thick layers of partially decomposed organic matter (peat)

• This is due to the cold, wet conditions that slow down decomposition rates, resulting in highly acidic and nutrient-poor soils

• Prairie soils in the Great Plains, USA:

• Soils known for their deep, dark topsoil have developed over a millennia

• This is due to the accumulation of organic matter from grassland vegetation and the semi-arid climate