Introductory Crop Physiology (1+1)

Factors affecting absorption of water

External factors
1. Available soil water
Sufficient amount of water should be present in the soil in the form that can easily be absorbed by the plants. Usually the plants absorb capillary water i.e. water present in films in between soil particles. Other forms of water in the soil e.g. hygroscopic water, combined water and gravitational water are not easily available to plants. Higher amount of water in the soil results in poor aeration of the soil retarding metabolic activities such as respiration in root cells and thereby the rate of water absorption is reduced.

2. Concentration of soil solution
Increased concentration of soil solution (due to presence of more salts in the soil) results in higher OP. If OP of soil solution will become higher than the OP of cell sap in root cells, the water absorption particularly the osmotic absorption of water will be greatly suppressed. eg. poor absorption of water in alkaline and saline soils.
3. Soil air
Absorption of water is reduced in poorly aerated soils due to the deficiency of O2 and consequently, the accumulation of CO2 will retard the metabolic activities like respiration in roots. This also inhibits rapid growth and elongation of the roots and deprived of fresh supply of water in the soil. Water logged soils are poorly aerated and hence, are physiologically dry.

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4. Soil temperature

Increase in soil temperature up to about 30°C favours water absorption. At higher temperature, water absorption is decreased. At low temperature also water absorption decreased and at about 0°C, it is almost stopped. This is because at low temperature,

a. The viscosity of water and protoplasm is increased
b. Permeability of cell membrane is decreased
c. Metabolic activity of root cells are decreased
d. Root growth and elongation of roots are checked.
Internal Factors

1. Transpiration

The rate of absorption of water is directly proportional to transpiration. The higher transpiration rates produce a tension or pull that is transmitted to roots through hydrostatic system of plants creating a favourable condition for entry of water.

2. Absorbing root systems

The number of root hairs accounts for the entry of water in the plant system. The development of root hairs depends upon the environment, especially moist condition.

3. Metabolism

The metabolism and absorption are closely related. The factors inhibiting rate of respiration such as poor aeration, anesthetics and KCN reduces the absorption rate.

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