SOIL:Organizing Component for Terrestrial Ecosystem

Atmosphere Hydrosphere Pedosphere

ECOSPHERE

SOILThe net result of the action of climate and organisms, especially vegetation and microbes, on the parent material of the surface of the Earth.

It is composed of a parent material – the underlying geological or mineral substrate – and an organic component in which organisms and their products intermingled with the finely divided and modified parent material.

SOIL HORIZONSOIL PROFILE

O Horizon

O Horizon is generally only a few centimeters thick, consists of organic matter. The remains of the plant materials are clearly recognizable in the upper part of the O Horizon, but its lower part consists of humus.

A Horizon (Top Soil)

A Horizon is composed of the bodies of plants and animals that are being reduced to finely divided organic material by humification.

Litter

Humus

Leached zone

Leaf mold

A-0 Horizon

The litter represents the detritus component and can be considered a sort of ecological subsystem in which microorganisms (bacteria and fungi) work in partnership with small arthropods (soil mites and collembolans) to decompose the organic material.

B Horizon

B Horizon is composed of mineral soil in which the organic compounds have been converted by decomposers into organic compounds (mineralization) and thoroughly mixed with divided parent material.

B Horizon

The soluble materials of the B horizon are often formed in the A horizon and deposited or leached by the downward flow of water into the B horizon.

C Horizon

C Horizon is the more or less unmodified parent material. This parent material may represent the original mineral formation that is disintegrating in place, or it may have been transported to the site by gravity, water, glaciers, or wind.

The soil profile and the relative thickness of the horizons are generally characterized by :

• Climatic Regions• Topographical Situations

SOIL

3 Important Attributes to be measured in the A and B Horizons:

1. Texture2. Percentage of Organic Matter3. Exchange Capacity

SOIL

Soil erosion caused by water and wind occurs naturally at low rates all the time resulting from great floods, glaciers, volcanic eruptions, and other episodic events.

SOIL Displacement: Natural and Human-Accelerated

Areas that lose soil faster than the new soil is formed generally suffer reduced productivity and other detrimental effects.

Areas receiving too much soil may also be negatively affected. However, fertility may be enhanced when soils are washed down from hills into river valleys and deltas or are deposited on prairies by winds.

As is the case for so many natural processes, humans tend to accelerate soil erosion, often to our long-term detriment.

SOIL Quality: Indicator of Environmental Quality

In the closing years of the 20th century, scientific attention and publicity on high-yielding crop varieties diverted attention from the fact that maintaining high yields depends on maintaining soil quality, which, in turn, depends on sustainable tillage and diversity both at the crop and landscape levels.

As soil is the chief organizing center foe terrestrial and wetland ecosystems, soil quality should be a good indicator of environmental quality in general. In other words, if the quality of the soil is being maintained, then whatever is going on to the landscape, whether natural or managed, should be sustained.