Soil sci. question: how does the E horizon form?

Question

I'm not cheating on my homework. I'm revising and this bit doesn't make sense to me. It doesn't seem to explain it in the textbook. The E horizon is a level at the base of the topsoil which is a strongly leached.

Answer 1

Soil Horizons (layers): Soil is made up of distinct horizontal layers; these layers are called horizons. They range from rich, organic upper layers (humus and topsoil) to underlying rocky layers ( subsoil, regolith and bedrock).

O Horizon - The top, organic layer of soil, made up mostly of leaf litter and humus (decomposed organic matter).

A Horizon - The layer called topsoil; it is found below the O horizon and above the E horizon. Seeds germinate and plant roots grow in this dark-colored layer. It is made up of humus (decomposed organic matter) mixed with mineral particles.

E Horizon - This eluviation (leaching) layer is light in color; this layer is beneath the A Horizon and above the B Horizon. It is made up mostly of sand and silt, having lost most of its minerals and clay as water drips through the soil (in the process of eluviation).
==The Mineral Soil Horizons
The lower layers of mineral soil (the E, B and C horizons) that have been little changed from the nature of soil that was deposited by glaciers or by rivers and lakes since glacial retreat called parent material. Depending on what was left when the glaciers retreated in any given location, the mineral soil layers may be composed of clay, silt, sand, pebbles, gravel, boulders, or some combination of these. The most important distinction between the mineral soil horizons and the upper soil horizons is that mineral soil doesn't contain much decomposed organic material. So, the color is usually much lighter than the black color of the A horizon.
The E horizon develops beneath the A horizon with a total thickness of up to 20 centimeters or more. This layer of mineral soil looks more like unaltered soil (parent material) that was left after the glaciers left this area, but has a distinctive gradient of color from top to bottom. The top of the E horizon is dark black or gray in color (very similar to the A horizon color) and gets lighter in color as soil depth increases. The dark color comes from organic molecules carried down from the A horizon with water as it moves down through the soil layers in the process called leaching.
When earthworms invade, they mix the top of the E horizon with the O Horizon to form the new A horizon. Then the process of leaching starts again and a new E horizon forms beneath the new A horizon. It looks pretty much the same as it did before, but now it is lower in the soil. However, if deep dwelling earthworm species are present, the new E horizon may be laced with earthworm burrows which appear darker in color because they are lined with the earthworm cast material.


B Horizon - Also called the subsoil - this layer is beneath the E Horizon and above the C Horizon. It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate) that it receives from layers above it when mineralized water drips from the soil above.

C Horizon - Also called regolith: the layer beneath the B Horizon and above the R Horizon. It consists of slightly broken-up bedrock. Plant roots do not penetrate into this layer; very little organic material is found in this layer.

R Horizon - The unweathered rock (bedrock) layer that is beneath all the other layers.

Answer 2

Soil horizons have different compositions, soil types, and environments.Soil begins as weathered rock. As plants are introduced, the A-horizon composed of dead organic matter appears. Sand is worn down into smaller silt by rain and water. This makes the complete a-horizon. As groundwater seeps and adds new minerals, the b-horizon starts to form. Iron and clay particles settle to the bottom above bedrock. As these proceses continue, the horizons get more pronounced and deeper.

Answer 3

E Horizon..... lets see... you already know what an e-horizon is...(mineral horizon of strong eluviation), so, it is formed when organic acids from the A or O horizon combine with leaching waters, to weather and mobilize silicate clays, iron and aluminum, leaving a bleached layer of resistant minerals such as quartz.

Does this anwer your question?

Answer 4

A soil horizon is a specific layer in the soil which parallels the land surface and possesses physical characteristics which differ from the layers above and beneath. Horizon formation is a function of a range of geological, chemical, and biological processes and occurs over long time periods. Identification and description of the horizons present at a given site is the first step in classifying a soil at higher levels, through the use of systems such as the USDA Soil Taxonomy or the Australian Soil Classification.

The term 'horizon' describes each of the distinctive layers that occur in a soil. Each soil type has at least one, usually three or four different horizons and these are described by soil scientists when seeking to classify soils (Soil-Net). Horizons are defined in most cases by obvious physical features, colour and texture being chief among them. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material, ie, ‘coarser’ or ‘sandier’ than the horizons above and below.

Most soils conform to a similar general pattern of horizons, often represented as an ‘ideal’ soil in diagrams. Each main horizon is denoted by a capital letter, which may then be followed by several alphanumerical modifiers highlighting particular outstanding features of the horizon. While the general O-A-B-C-R sequence seems fairly universal, some variation exists between the classification systems in different parts of the world. In addition, the exact definition of each main horizon may differ slightly – for instance, the US system uses the thickness of a horizon as a distinguishing feature, while the Australian system does not. It should be emphasised that no one system is more correct – as artificial constructs, their utility lies in their ability to accurately describe local conditions in a consistent manner.