write a short note of A horizon and B horizon
Answers
Explanation:
B horizons: are commonly referred to as the subsoil. They are a zone of accumulation where rain water percolating through the soil has leached material from above and it has precipitated within the B horizons or the material may have weathered in place. Well drained soils typically have the brightest color development within the B horizons.
Field criteria:
Subsurface horizon formed below an O, A and/or E horizon and above the C layer.
In well drained soils, the B horizon is typically a yellowish brown to strong brown color and is commonly referred to as the subsoil.
B - horizons have material (usually iron but also humus, clay, carbonates, etc.) which has moved into it (Illuviation) they also have structure development in some pedons.
Within New England, B horizons typically extend to a depth of 2 to 3 feet below the surface.
The A and B horizons together are called the soil solum.
From Soil Taxonomy:
B horizons: Horizons which have formed below an A, E, or O horizon; they are dominated by the obliteration of all or much of the original rock structure and show one or more of the following:
(1) Illuvial concentration of silicate clay, iron, aluminum, humus, carbonates, gypsum, or silica, alone or in combination;
(2) Evidence of removal of carbonates;
(3) Residual concentration of sesquioxides;
(4) Coatings of sesquioxides that make the horizon conspicuously lower in color value, higher in chroma, or redder in hue, without apparent illuviation of iron, than overlying and underlying horizons;
(5) Alteration which forms silicate clay or liberates oxides, or both, and which forms a granular, blocky, or prismatic structure if volume changes accompany changes in moisture content; or
(6) Brittleness.
All the different kinds of B horizons are, or were originally, subsurface horizons. Included as B horizons, where contiguous to other genetic horizons, are layers of illuvial concentration of carbonates, gypsum, or silica which are the result of pedogenic processes (and may or may not be cemented), and brittle layers that show other evidence of alteration, such as prismatic structure or illuvial accumulation of clay.
Examples of layers that are not B horizons are: layers in which clay films either coat rock fragments or cover finely stratified unconsolidated sediments, regardless of whether the films were formed in place or by illuviation; layers into which carbonates have been illuviated but which are not contiguous to an overlying genetic horizon; and layers with gleying but no other pedogenic changes.
sufficiently deep cut into the soil usually shows some fairly distinct layers. The action of physical, chemical and organic processes leads to the formation of well-developed layers one below and other.
ADVERTISEMENTS:
Each layer is distinguished from the other by its colour and the size of particles. These layers are called horizons, and their arrangement is called the soil profile. In a typical mature soil there are four horizons, designated (from the surface downward) as A, B, C, and R. In some soil the A and B horizons may have finer subdivisions.
(i) Top Soil:
The A horizon is the layer also called the topsoil. It is usually distinguished from the other horizons by its colour, texture, and structure and is rich in humus and under composed organic matter. There is an abundance of plant root and living organisms. The colour of the top soil is determined by its drainage.
(ii) Sub Soil:
The B horizons, also called subsoil, usually is finer in texture than the A horizon and has less humus and undecomposed organic matter and fewer plant roots and living organisms.
(iii) Bed Rock:
ADVERTISEMENTS:
The C horizon consists of parent material that has been changed very little by soil forming processes. Some soil never develop a B horizon. The R horizon consists of unweathered bedrock.
Short note on A horizon and B Horizon
A Horizon⇒ The A horizon is the layer also called the topsoil. It is usually distinguished from the other horizons by its colour, texture, and structure and is rich in humus and under composed organic matter. There is an abundance of plant root and living organisms. The colour of the top soil is determined by its drainage.
B Horizon⇒ The B horizon is the second and middle zone, characterized by an accumulation of soluble or suspended organic material, clay, iron, or aluminum. These materials originate in the A horizon and are transported to the B horizon through the process of eluviation.