Which horizon occurs directly above bedrock

The horizons are:. O humus or organic : Mostly organic matter such as decomposing leaves. The O horizon is thin in some soils, thick in others, and not present at all in others. A topsoil : Mostly minerals from parent material with organic matter incorporated. A good material for plants and other organisms to live. E eluviated : Leached of clay, minerals, and organic matter, leaving a concentration of sand and silt particles of quartz or other resistant materials — missing in some soils but often found in older soils and forest soils.

B subsoil : Rich in minerals that leached moved down from the A or E horizons and accumulated here. R bedrock : A mass of rock such as granite, basalt, quartzite, limestone or sandstone that forms the parent material for some soils — if the bedrock is close enough to the surface to weather.

This is not soil and is located under the C horizon. Back to Soil Basics page. Because of their organic content, these horizons are typically black or dark brown in color. The dominant processes of the O horizon are additions of organic matter, and transformations from fibric to sapric.

E: The E horizon appears lighter in color than an associated A horizon above or B horizon below. An E horizon has a lower clay content than an underlying B horizon, and often has a lower clay content than an overlying A horizon, if an A is present. E horizons are more common in forested areas because forests are in regions with higher precipitation and forest litter is acidic.

However, landscape hydrology, such as perched water tables, can result in the formation of an E horizon in the lower precipitation grasslands, as seen in the profile below. The dominant processes of an E horizon are losses. R: An R layer is bedrock. When a soil has direct contact with bedrock, especially close to the soil surface, the bedrock becomes a variable when developing land use management plans and its presence is noted in the soil profile description.

A Incorrect: This layer is deep within the soil profile and has little organic matter. A horizons have more OM compared with other horizons except the O. B Incorrect: A B horizon has evident soil activity such as color development, clay increase, or structure. C Correct: The clue is that there is no soil development so the sand is unaltered parent material. This is a C horizon. E Incorrect: No information is presented to suggest that this layer has been stripped of clay, iron, and OM like an E horizon.

O Incorrect: This is a mineral layer and has little OM. An O horizon would be mostly OM. R Incorrect: This is not bedrock. Looks Good! Correct: The clue is that there is no soil development so the sand is unaltered parent material.

A Incorrect: While the soil color is brown, the main process here is accumulation of clay and development of prismatic structure. An A horizon often shows a loss of clay when compared to underlying horizons and rarely would an A have prismatic structure; they tend to have granular structure. B Correct: Accumulation of clay represents translocation within the soil profile. The layer in which the clay accumulates would be a B horizon. The development of strong prismatic structure would also support the B horizon designation.

C Incorrect: The accumulation of clay and structure indicates soil development, something a C horizon lacks. E Incorrect: E horizons are zones of loss and will not have clay accumulation. O Incorrect: An O horizon would be mostly organic matter and likely darker in color, the layer here is mostly mineral material. Correct: Accumulation of clay represents translocation within the soil profile. A Correct: Granular structure and increased organic matter in a mineral sand, silt, clay layer is a good indication of an A horizon.

Another clue from this picture is the earthworm, these creatures like to be in soil layers that have plenty of food, which for them is organic matter. B Incorrect: The A horizons typically develops granular structure while the B horizon would have blocky, prismatic, platy, or columnar structure. C Incorrect: This layer is close to the surface and accumulating organic matter. C horizons are not zones of accumulation.

O Incorrect: This is a mineral layer. Correct: Granular structure and increased organic matter in a mineral sand, silt, clay layer is a good indication of an A horizon. A Incorrect: The described layer is all organic.

An A horizon has a strong mineral component. B Incorrect: A B horizon is mineral soil and has evident soil activity such as color development, clay increase, or structure. C Incorrect: A C horizon is a mineral layer and has little OM accumulation or any other soil development. O Correct: Horizons that are made up mostly of decomposing organic matter in the yellow box are O horizons.

The most likely candidate for the horizon under this O horizon is an A horizon, which owes its dark color to the organic matter that coats the surfaces of the sand, silt, and clay particles. Correct: Horizons that are made up mostly of decomposing organic matter in the yellow box are O horizons. Previous Page Next Page.