Water is mainly obtained through rain. Some of the water goes into the reservoirs. This is called run off or Run away water. Rest of the water enter into the land. Soil water is the term for water found in naturally occurring soil. Soil water is also called rhizic water. There are three main types of soil water – gravitational water, capillary water, and hygroscopic water – and these terms are defined based on the function of the water in the soil.
TYPES OF SOIL WATER:-
(a) Gravitational water:
Form of water, which reaches at the soil water table due to the gravitational force after the rainfall. This form is not available to plants but available by mechanical methods or by tube well irrigation. This is a free form of water which is held loosely in soil
(b) Hygroscopic water:
Thin film of water is tightly held by the soil particles is called hygroscopic water. This water is also not available to the plants. This type of soil water is bound so tightly to the soil by adhesion properties that very little of it can be taken up by plant roots. Since hygroscopic water is found on the soil particles and not in the pores, certain types of soils with few pores (clays for example) will contain a higher percentage of it.
(c) Chemically combined water:
The amount of water present in the chemical compounds, which are present in the particles of soil. This is not available to the plants.
(d) Capillary water:
Water exists between soil particles in small capillary pores is called Capillary water. It is the most common available form of water for absorption. Capillary water is held in the soil because the surface tension properties (cohesion and adhesion) of the soil micropores are stronger than the force of gravity. However, as the soil dries out, the pore size increases and gravity starts to turn capillary water into gravitational water and it moves down. Capillary water is the main water that is available to plants as it is trapped in the soil solution right next to the roots if the plant.
(e) Atmospheric humidity:
This is water vapor present in air, which can be absorbed by hanging roots of the epiphytes due to presence of spongy velamen tissue and hygroscopic hairs.
