ABSORPTION OF WATER
Land plants absorb water mainly from the soil. The soil plays important role in water storage, and serves as a medium for root growth. It is also a reservoir of mineral nutrients and provides anchorage for plants. The ultimate source of water for the soil is rain or irrigation. A part of rainwaterl-surface, along the slope and is called run-away water or run-off.
Water in the soil is known as soil water or soil solution. The total amount of water present in the soil is called holard.
The amount of water available to the plants is called chresard (available water). The amount of water which cannot
be absorbed by the plant is called echard (unavailable water) Water that occurs freely in the pervious rocky matter is called ground water. The upper layer of ground water is called water table, where soil is completely saturated with water and air is excluded. Very few plants can send their roots upto the fringe of the water table, due to deficiency of air. ine plants which do so, are called phreatophytes,
eg., Populus deltoides
Water is present in the soil in five forms- capillary water, gravitational water, hygroscopic water, combined water and water vapours.
Capillary water is present in soil narrow spaces or micropores of soil (diameter s 20 um), held by capillary forces Only capillary water is available to plant roots for absorption.
The per pert dry weight of soil, after the stoppage of gravitational flow is called field capacity. Soil moisture, bevon field capacity, produces water logging.
if soil water is not replenished wilted and die. It is known as permanent wilting percentage (PWP) or permanent wiltin
does not enter the soil, but is drained away from optimum or maximum amount of water retained from time to time, a stage is reached when the plants growing in it become permanently) or the influence of gravity. Thus, gravitational water isn
upto the reach of the roots.
The surface layer of soil is temporarily saturated by water, which gradually percolates down, under ot readily available to the plants and penetrates soil, below up to the reach of
roots.
