Plants absorb water for development. Only a few xerophyte plants exist in arid climate which can grow without suction of water.
In many plants, transpiration is equal to available quantity of water. Kremer (1969), through one study explained that a maize plant transpires 2 to 4 liter water (double its weight) on a dry and hot day.
If such transpired quantity of water were not re-supplied, the plants would either wither away or die. Transpiration mainly depends on physical factors.
Absorption of water in soil cells is in the direction of decreasing water potential gradient. Hence, such absorption is of two types:
1. Passive Absorption:
Due to water losses because of transpiration of water from plants, when water potential falls in cells of plant leaves, water potential falls to low level in the plant leaves.
2. Active Absorption:
In dry and humid soil as well as moist environment, transpiration is minimum. In such conditions, absorption is called active absorption. According to Kremer (1969), active absorption is less important in water economy of plants.
It happens in the following manner:
(i) Absorption due to seepage activeness of main cells.
(ii) Absorption due to ordinary osmotic reactions.
Transpiration of water is affected by the following factors:
1. Development of Roots:
Plants absorb water through their roots. Plants having deeper and extended roots can absorb water as per their requirement whereas plants having less deep roots can absorb lesser water.
2. Availability of Soil Water:
Quantum of water absorption capacity of plants is determined by existence of water in the soil. Necessary) water is decided by interrelation between wilting point and area capacity but its quantity depends on type and composition of soils found in different areas. Soils having different structure and composition have different water retaining capacity. Sandy soils retain less water whereas loamy soils retain more water.
3. Soil Temperature:
Soil temperature has direct as well as indirect effect on water absorption. Root growth stops with lower temperature and hindrances are created in the water flowing towards roots, which affects active absorption. Higher temperature has also adverse effect. Good aeration arrangement in soil provides active support in absorption of water.