Soil is the major source of water for plants. The plants absorb water through root hairs from the soil. The total water content present in the soil is called holard. Out of this, the water which can be absorbed by plants is chresard and remaining is called echard.
Broadly we can recognize the following sources of water for plants:
Gravitational Water
When the water enters the soil and passes through the spaces between the soil particles and reaches the water table, the type of soil water is called gravitational water. This water lies far below and is generally not available to the plant roots.
Hygroscopic Water
This is the form of water which is held by soil particles on soil surface. The water is held tightly around the soil particles due to cohesive and adhesive forces. These forces greatly reduce the water potential and thus this type of water in soil is not available to plants.
Capillary Water
In smaller pores of the soil, water is held against the force of gravity by capillary forces and is called capillary water. This form of water is most important to plants and constitutes the only available source of water to plants.
Run Away Water
All the rain water falling on the soil is not retained by it. Run away water does not enter the soil and gets drained away from soil surface.
Combined water
Some water is present in the form of hydrated oxides of aluminium, iron, silicon inside the soil. This is also a non-available form of water for plant roots.
Diagram Showing Different forms of Soil Water and their Possible Relationship with Soil and Plant Water Status
Seedling Showing Terminal Portion of Root Showing Root Hair Zone
