Plants absorb water from the soil by means of roots and root hairs. The main source of water in soil is rainfall. The total amount of water present in the soil is termed as holard. Out of this, the available water to the plants is called the chesard and which can not be absorbed is termed as chard when rain falls on soil surface, a part of water drains away.
It is known as run-away water which is not available to plants. A part of rain water percolates downwards through large pores between the soil particles under the influence of gravity which is called gravitational water. It accumulates in the water table much below the reach of root system.
This water is of no use to the plants. However, a good amount of water is retained by the soil particles and is known as field capacity moisture. This water may be present in three forms. Capillary water, hygroscopic water and chemically combined water. Water which fills the spaces between non colloidal soil particles is known as capillary water.
It is the available water for the plants. Roots and root hairs enter into the capillaries of the soil particles to absorb this water. Water which is held by soil particles of colloidal complex due to adhesive force constitutes hygroscopic water. Hygroscopic water-is of no use to plants.
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A small portion of water is chemically bound with the soil elements. it mostly occurs in the form of oxides of aluminum, iron, silicon etc. This water is practically not available to plants.