Plants absorb water from the soil by their roots. The water is found in different forms in the soil. The chief source of water to the soil is rain. After the rains, a part of the water drains away. This is called runaway water and it is not available to the plants. A part of the water percolates downwards through large pores between the soil particles under the influence of gravity and is known as gravitational water. It reaches the low water table and goes beyond the root zone. Alternatively, a good amount of water is retained by the soil particles and is called Field Capacity moisture, i.e., the water retained due to the water-holding capacity of soil particles.

This water may be present in three forms: Capillary water, Hygroscopic water, and Chemically combined water. Of all these, the water available to the plants is capillary water which fills the space between the non-colloidal smaller particles of soil. Hydroscopic water is held by the soil particles of colloidal smaller particles of soil. Hygroscopic water is held by the soil particles of the colloidal complex due to adhesive force. The roots can not draw this.

Field Capacity and Water Holding Capacity of Soil

It is defined as the amount of water retained by the soil after the grainage of gravitational water has become very slow. The field capacity is affected by soil profile, soil structure, and temperature. For example, fine-textured soil overlying coarse-textured soil will have a higher field capacity than uniformly fine-textured soil. It also depends upon the size of the soil particles, e.g., 5% in sandy soil, 35% in loamy soil, 45% in clay soil, and negligible in gravel and rocks.

Water Holding Capacity :

In fully saturated soils, the %age of moisture held in the form of the film is called Water Holding the capacity of the soil.

Permanent Wilting Point or Wilting Co-efficient :

It is the percentage of soil water left after the plant growing in that soil has permanently wilted. It depends on the osmotic characteristics of the plant. Therefore, different plants if grown in the same soil will wilt at different times depending upon their osmotic potential after the water supply to the soil is stopped.

Water Absorbing Parts of Plant

The major portion of water required by the plants is absorbed by the roots. But the absorption of water by leaves and stem has also been found in a few plants. Hydrophytes absorb by general (Left) surface.

The uptake of water by leaves is influenced by :

i. Structure and permeability of cuticle and epidermis

ii. Hairiness of leaf surface.

iii. Case of the wetting surface.

iv. Internal environment of deficiency of water in parenchymatous cells closes to the epidermis.

Roots play the principal role in the absorption of water. Even orchids develop modified roots for the purpose of absorbing water from the atmosphere. This type of specialized water-absorbing water from the atmosphere. This type of specialized water-absorbing tissue present around the cortex of the roots is called Velamen. It consists of thin-walled parenchymatous cells and the moisture absorbed by it is transferred to the root xylem through exodermis, cortex, endodermis, and the pericycle.

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