The major sources of water available either for agriculture or for human consumption is obtained from the precipitation in the form of rainfall or snowfall. Run-off from precipitation drains through streams and rivers or collects in surface depressions forming tanks or ponds. Water of streams stored in reservoirs or is diverted directly through canal system for irrigation. Run-off water stored in tanks or ponds is also regulated for irrigation through suitable conveyance system. Part of rainfall is stored as a Ground water. Of the annual rainfall of 400 (m. ha. m) about 215 (m. ha. m) infiltrates into the soil. A major part of it amounting to about 165 (m. ha. m) is retained as a soil moisture, which is essential for growth of vegetation. It is only after the soil has absorbed water to field capacity that water starts percolating down to water table and adds to ground water reservoir.
Functions of water:
The distribution of vegetation over the surface of earth is controlled by the availability of water than any other single factor. In heavy rainfall area, flush vegetation (forest) is observed.
The ecological importance of water is result of physiological importance.
It is a constituent of protoplasm:
Water is as important quantitatively as qualitatively Constituting 80 to 90 Percent of fresh weight of most herbaceous plant parts and 50 percent of the fresh weight of woody plant.
It is a very good solvent:
Water acts as a solvent in which gases, minerals (plant Nutrients) and other solutes are dissolved. The dissolved plant nutrients are absorbed by Plant through soil solution. It acts as a carrier of food nutrients.
It is a reagent:
Water acts as a reagent in many important processes, such as photosynthesis and hydrolysis of starch and sugar.
It maintains turgidity of plant:
Maintenance of turgidity is essential for cell Enlargement and growth. Turgidity is also important in opening of the stomata, movement of leaves, flower, petals etc.
It controls the temperature of plant and soil.
It is a major part of plant body