Question

------is the main source of water for plant

Answer 1

Complete question:

     is the main source of water for the plant.

[I] Gravitational water

[II] Capillary water

[III] Hygroscopic water

[IV] Combined water

Answer:

[II] Capillary water is the main source of water for the plant.                       

Explanation:

The principal source of soil water is rain or precipitation.

Some of the rainwater runs off the surface due to natural slopes and gets collected in water reservoirs such as lakes, rivers ponds, etc.

It is called run-away water and is not available to the plants. The rest of the water which is held by the soil particles occurs in the following forms:

[I] Gravitational water

• After heavy rainfall, an appreciable amount of water moves deep down the soil due to gravitational force. It is called gravitational water.

• It accumulates in the deep situated zone of the earth, called the water table or groundwater.

• It lies beyond the reach of the water-absorbing roots and, therefore, is non-available to plants.

[II] Capillary water

• This water is held by the thin capillaries (i.e., pore spaces) formed by the soil particles after the movement of gravitational water has stopped.
• Capillary water is the major, available source (Chesard) of water for plants.

[III] Hygroscopic water

• The water held tightly in the form of a thin film around the soil particles is called hygroscopic water.

• It is held tightly around the particles as a result of cohesive and adhesive forces and can not be easily removed by the plants. Hence, it is not available to plants.

[IV] Combined water

• This is the form of water that forms the chemical composition of soil particles.

• It occurs in the form of hydrated oxides of aluminium, iron, silicon, etc. This form of water is also not available to the plants.

Therefore the right answer is the option [II] Capillary water.

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Answer 2

Answer:

Rainwater is the main source of water for plant.

Explanation:

• A plant uses a mechanism called transpiration in which internal water evaporates off the surface of the leaves in response to solar heat.
• Thus, subsurface water participates in the water cycle with the help of transpiration.
• Rainwater is the primary supply of water for the soil, according to the facts above.

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