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How the Edaphic factors affect the plants?

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Soil is a upper most layer of weathered Earth crust in which plants grow. It is a complex composite mass of minerals and degraded organic material. The study of soil is called as pedology. The foundation of pedalogy was laid by Russian scientist Dokuchaw (1889). According to him, soil is the result of interaction among mother rocks, environment, organisms & time. The formation of soil as a result of weathering of rocks is called as pedogenesis. The rock is an aggregation of minerals which degrades constantly which is called as degradation. Three main factors participate in this process viz.-

  1. Physical factors : Such as air. precipitation, temperature, landslide etc.
  2. Chemical factors : Such as hydrolysis, oxidation, catabolism, hydration, carbonization etc.
  3. Biological factors : Moss, blue green algae, mining etc.

Formation of soil is a continuous but a very slow process. On the basis of formation & origin of minerals, the soil is of two types (a) Residual soil : The soil that remains in the place of its origin.
(b) Transported soil : The soil that has been transported from other places by many ways. It is of four types viz.-

  • Alluvial soil : The soil which is transported by water.
  • Glacial soil : Transported by glaciers.
  • Colluvil soil : Transported by Earth’s gravity.
  • Aeolian soil : Transported by air.

Soil Profile :
A soil profile makes up a distinct layer of soil. It runs roughly parallel to the soil surface and has different properties and characteristics than the adjacent layers above & below. The soil profile is a vertical section of the soil that depicts all its horizons. These horizons are as follows :

1. Horizon ‘A’ :
It is the uppermost layer which is also called as top soil It allow s plants to grow. It is formed by the interaction of rock degradation, activities of the organisms. It is rich in humus. It is dark brown in colour.

2. Horizon ‘B’ :
It is situated below the top soil & also called as subtop soil. It is light brown in colour & denser than top soil. If is life less i.e. without organisms. It contains fine rock particles & soluble minerals. It stores the rain water & acts as water reservoir. This water gradually reach up to the top soil by capillary action.

3. Horizon ‘C’ :
It is the lowermost stratum of the soil profile which is of less important concerning to life. Sometimes long roots of plants are found in it. It is followed by hard rocks.

The top soil is comparatively thicker in the grasslands. The soil devoid of vegitation is without top soil, hence the subtop soil becomes uppermost.

Composition of soil :
Normally, the garden soil consists of four main components-

  1. Mineral components (40% by volume)
  2. Soil organic matter (10% by volume)
  3. Soil water (25% by volume)
  4. Soil air (25% by volume)

They are called as soil factors and they vary qualitatively & quantitatively according to the ecological conditions. In addition, soil temp., soil organisms & soil activities also help in plant growth

1. Mineral Components & Soil texture :
The minerals are the derivatives of the rock. The size of minerals particles is variable and it affects the soil properties.
Chemically, gravel and sand are inert Dead granules are normally made up of oxides of aluminium & silicon. The relative ratio of mineral particles of various sizes determines the soil texture. Pebbles & gravel are not considered in textural classes.

The soil texture decides the water holding, nutrients & growing plants of the soil.
On the basis of relative ratio of rock particles, the soil is of six types –

  • Sandy soil : In includes sand particles. It has sufficient soil air but its water & nutrients holding capacity is less.
  • Clay soil : It mainly includes clay. It’s water holding capacity is high but the aeration is less. It is not suitable for plants to grow.
  • Loam soil : It includes equal quantity of silt & clay. It has moderate aeration & water holding capacity. Hence, it is suitable for plants to grown.
  • Sandy loam soil : It is a loam soil with more soil particles.
  • Silt loam soil : It is a loam soil with more silt granules.
  • Clay loam soil : It is a loam soil with more clay.

2. Soil Organic Matter :
It is also called as humus. It is essential for soil fertility. The decaying organic material of dead organisms is called as humus. It is formed by degradation of remnants of plants and animals, and excreta of animals. Earthworms, microorganisms like bacteria & fungi utilize the humus as food. Formation of humus is called as humification and conversion of humus into mineral salts is called as mineralization. The Humus is of two types :
(a) Mor humus : It is raw humus. It has less mineral salts & microorganism or animals are almost absent.
(b) Mull humus : It is a granular & mature humus. It harbors microorganisms & earthworm abundantly.

3. Soil Water :
The main source of soil water is rain. After heavy rain some of the water flows down which is called as run off water. It is not easily available to the plats. Some water under the influence of gravity reaches unto the water table and it is called as gravitational water. It is also not available easily to the plants. Some part of the rain water occupies the spaces in between the colloidal granules of soil or forms thin layer surrounding the granules. It is called as capillary water. It is easily available to the plants and is of much importance. It is absorbed easily by the roots. Some of the soil water is absorbed by soil colloids which help to bind these particles. It is called as hygroscopic water. It is not available to the plants. Some of the soil water is associated with the mineral molecules. It is called as chemically combined water. It is not absorbed by the roots. To conclude, out of all types of soil water only capillary water is used by the plants.

Soil water holding or Field Capacity (FC) :
Field capacity is the amount of soil water held in the soil after excess water drained away.

Field Capcity ⇒ Capillary water + Hygroscopic water + Chemically combined water + Water vapor

The total of hygroscopic water and capillary water is called as soil water holding capacity. The mineral point of soil moisture the plant requires not to wilt is called as permanent wilting point (PWP). If moisture decreases to this, a plant wilts and can no longer recover its turgidity. The percent hurnidy of soil at which the plant first develops permanent wilting is called as wilting coefficient.

The part of soil water which can be absorbed by plants is called as available water, normally it is capillary water. The part of soil water which cannot be absorbed by the plants is called as non-available water. In other words, the total amount of soil water is called as holard. the part of water that can be absorbed is called as chresard and the part which cannot be absorbed is called as Echard.

Proper growth of plants require a sufficient amount of water. Excess of soil water i.e. water logging reduces the air spaces and roots get damaged. The water absorption is affected and the plant growth is highly reduced. This type of land is called as physiologically dry land.

4. Soil air :
The soil is porous and there are air spaces in between the soil particles which are occupied by either water or air. The amount of soil air depends upon the size of these pores. The soil oxygen is essential for germination of seeds,’ root growth, soil fertility, humus formation, development of root hair, nitrogen fixation by bacteria, absorption by roots etc. Diminished aeration causes morphological & anatomical modifications such as presence of pneumatophores in mangroove plants. The hydrophytes have a developed system spaces that helps to provide O2 to the submerged roots.

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