Soil Water: Potential and Importance

After reading this article you will learn about the potential and importance of soil water.

Potential of Soil Water:

The retention and movement of water in soils, its uptake and translocation in plants and its loss to the atmosphere are all energy-related phenomena. The more strongly water is held in the soil, the greater is the heat (energy) required. In other words, if water is to be removed from a moist soil, work has to be done against adsorptive forces.

Conversely, when water is adsorbed by the soil, a negative amount of work is done. The movement is from a zone where the free energy of water is high (standing water table) to one where the free energy is low (a dry soil). This is called soil water energy concept.

Free energy of soil water is affected by:

(i) Matric (solid) force i.e., the attraction of the soil solids for water (adsorption)— which markedly reduces the free energy (movement) of the adsorbed water molecules,

(ii) Osmotic force i.e., the attraction of ions and other solutes to reduce the free energy of soil solution. Matric and Osmotic potentials are negative and reduce the free energy level of the soil water. These negative potentials are, referred as suction or tension,

(iii) Force of gravity acts on soil water, the attraction is towards the Earth’s centre, which tends to pull the water downward. This force is always positive. The difference between the energy state of soil water and pure free water is known as soil water potential. Total water potential (Pt) is the sum of the contributions of gravitation potential (Pg), matric potential (Pm) and the osmotic potential (Po).

Pt = Pg + Pm + Po

Potential represents the difference in free energy levels of pure water and of soil water. The soil water is affected by the force of gravity, presence of soil (matric) and of solutes.

Importance of Soil Water:

Water is essential for all forms of life. Water plays a very significant role in soil-plant growth relationships.

There are following functions of water in plant growth and crop production:

1. Plant nutrients:

Water serves as a solvent and carrier of food nutrients for the growth of plants Water itself acts as a nutrient also.

2. Weathering process:

The process of weathering and soil formation depend on water.

3. Tillage operation:

Good tilth can be secured at right stage of moisture content.

4. Structure formation:

Water helps in good structure formation.

5. Physical, Chemical and Biological activity:

In fact, the soil water is a great regulator of physical, chemical and biological activities in the soil.

6. Microorganism activity:

The microorganism inhabiting the soil also require water for their metabolic activities.

7. Photosynthesis:

Water is essential for the process of photosynthesis.

8. Plant turgidity:

Water also maintains the turgidity in plant.

9. Seed germination and Plant growth:

Often an excess or deficit of water in the soil is a limiting factor in seed germination and plant growth.

10. Adverse effect:

Water protects plant from adverse conditions like drought, frost etc..