Dr. Archana Singh 1 SET- UPS 1. SOIL PROFILE “Soil profile is defined as the vertical section of the soil from the ground surface downwards to where the soil meets the underlying rock.” Soil Profile The soil is the topmost layer of the earth’s crust mainly composed of organic minerals and rock particles that support life. A soil profile is a vertical cross-section of the soil, made of layers running parallel to the surface. These layers are known as soil horizons. The soil is arranged in layers or horizons during its formation. These layers or horizons are known as the soil profile. It is the vertical section of the soil that is exposed by a soil pit. The layers of soil can easily be identified by the soil colour and size of soil particles. The different layers of soil are: Topsoil Subsoil Parent rock Each layer of soil has distinct characteristics. Soil profile helps in determining the role of the soil as well. It helps one to differentiate the given sample of soil from other soil samples based on factors like its colour, texture, structure, and thickness, as well as its chemical composition.
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Dr. Archana Singh
1
SET- UPS
1. SOIL PROFILE
“Soil profile is defined as the vertical section of the soil from the ground surface downwards to where the soil meets the underlying rock.”
Soil Profile
The soil is the topmost layer of the earth’s crust mainly composed of organic minerals and rock particles that support life. A soil profile is a vertical cross-section of the soil, made of layers running parallel to the surface. These layers are known as soil horizons.
The soil is arranged in layers or horizons during its formation. These layers or horizons are known as the soil profile. It is the vertical section of the soil that is exposed by a soil pit. The layers of soil can easily be identified by the soil colour and size of soil particles. The different layers of soil are:
Topsoil
Subsoil
Parent rock
Each layer of soil has distinct characteristics.
Soil profile helps in determining the role of the soil as well. It helps one to differentiate the given sample of soil from other soil samples based on factors like its colour, texture, structure, and thickness, as well as its chemical composition.
Dr. Archana Singh
2
Layers of Soil
The soil profile is composed of a series of horizons or layers of soil stacked one on top of the other. These layers or horizons are represented by letters O, A, E, C, B and R.
The O-Horizon
The O horizon is the upper layer of the topsoil which is mainly composed of organic materials such as dried leaves, grasses, dead leaves, small rocks, twigs, surface organisms, fallen trees, and other decomposed organic matter. It contains about 20 to 30% of organic matter. This horizon of soil is often black brown or dark brown in colour and this is mainly because of the presence of organic content.
The A-Horizon or Topsoil
This layer is rich in organic material and is known as the humus layer. This layer consists of both organic matter and other decomposed materials. The topsoil is soft and porous to hold enough air and water.
In this layer, the seed germination takes place and new roots are produced which grows into a new plant. This layer
consists of microorganisms such as earthworms, fungi, bacteria, etc.
The E-Horizon
This layer is composed of nutrients leached from the O and A horizons. This layer is more common in forested areas and has lower clay content.
The B-Horizon or Subsoil
It is the subsurface horizon, present just below the topsoil and above the bedrock. It is comparatively harder and compact than topsoil. It contains less humus, soluble minerals, and organic matter. It is a site of deposition of certain minerals and metal salts such as iron oxide.
This layer holds enough water than the topsoil and is lighter brown due to the presence of clay soil. The soil of horizon-A and horizon-B is often mixed while ploughing the fields.
The C-Horizon or Saprolite
This layer is devoid of any organic matter and is made up of broken bedrock. This layer is also known as saprolite. The geological material present in this zone is cemented.
The R-Horizon
It is a compacted and cemented layer. Different types of rocks such as granite, basalt and limestone are found here.
Expected Questions based on Soil Profile
• What does this set-up demonstrate? Define it.
• Name the different horizons from top to bottom.
• Write briefly about the zone of illuviation.
• Which horizon is called the zone of leaching and why?
• What is humus? Which layer consists of maximum humus?
The Raunkiær system is a system for categorizing plants using life-form categories, devised by Danish botanist Christen C. Raunkiær and later extended by various authors.
History It was first proposed in a talk to the Danish Botanical Society in 1904 as can be inferred from the printed discussion of
that talk, but not the talk itself, nor its title. The journal, Botanisk Tidsskrift, published brief comments on the talk by M.P. Porsild, with replies by Raunkiær. A fuller account appeared in French the following year.[1] Raunkiær elaborated further on the system and published this in Danish in 1907.[2][3]
The original note and the 1907 paper were much later translated to English and published with Raunkiær's collected works.[4][3][5]
Modernization Raunkiær's life-form scheme has subsequently been revised and modified by various authors,[6][7][8]but the main structure has survived. Raunkiær's life-form system may be useful in researching the transformations of biotas and the genesis of some groups of phytophagous animals.[9]
Subdivisions The subdivisions of the Raunkiær system are premised on the location of the bud of a plant during seasons with adverse conditions, i. e. cold seasons and dry seasons:
Phanerophyte
These plants, normally woody perennials, grow stems into the air, with their resting buds being more than 50 cm above the soil surface,[10]e.g. trees and shrubs, and also epiphytes, which Raunkiær later separated as a distinct class (see below).
Raunkiær further divided the phanerophytes according to height as
Megaphanerophytes,
Mesophanerophytes,
Microphanerophytes, and
Nanophanerophytes.
Further division was premised on the characters of duration of foliage, i. e. evergreen or deciduous, and presence of covering bracts on buds, for 8 classes. 3 further divisions were made to increase the total of classes to 12:
Phanerophytic stem succulents,
Phanerophytic epiphytes, and
Phanerophytic herbs.
Epiphytes
Epiphytes were originally included in the phanerophytes (see above) but then separated because they do not grow in soil, so the soil location is irrelevant in classifying them.
Chamaephytes
These plants have buds on persistent shoots near the soil surface; woody plants with perennating buds borne close to the soil surface, a maximum of 25 cm above the soil surface, e.g., bilberry and periwinkle.
Hemicryptophytes
Hemicryptophytes
These plants have buds at or near the soil surface, e.g. common daisy and dandelion, and are divided into:
Protohemicryptophytes: only cauline foliage;
Partial rosette plants: both cauline and basal rosette foliage; and
These plants have subterranean or under water resting buds, and are divided into:
Geophytes: rest in dry soil as a rhizome, bulb, corm, et cetera, e.g. crocus and tulip, and are subdivided into:
o Rhizome geophytes,
o Stem-tuber geophytes,
o Root-tuber geophytes,
o Bulb geophytes, and
o Root geophytes.
Helophytes: rest in marshy or wet soil, e.g. reedmace and marsh-marigold; and
Hydrophytes: rest submerged under water, e.g. water lily and frogbit.
Therophytes
These are annual plants that complete their lives rapidly in favorable conditions and survive the unfavorable cold or dry season in the form of seeds. Many desert plants are by necessity therophytes.
Aerophytes
Aerophytes were a later addition to the system.[11] These are plants that obtain moisture and nutrients from the air and rain. They usually grow on other plants yet are not parasitic on them. These are perennial plants whose roots atrophy. Some can live on mobile sand dunes. Like epiphytes and hemicryptophytes, their buds are near the soil surface. Some Tillandsia species are classified as aerophytes.
Expected Questions based on Raunkier’s Life Form
• What does this set-up demonstrate?
• On what basis is the distribution made?
• Name the different forms with one example each.
• What does this set-up demonstrate?
• Name the scientist who has given this classification?