Matric Potential (ym)
- The matric potential is developed due to the attraction of water to solid surfaces which has major role in the retaining water in soil and soil water movement.
- Refers to the component of soil water potential resulting from adhesion (attraction of water to soil particles) and capillarity (water movement in small pores due to surface tension).
- Energy Loss: Adsorbed water loses energy as heat of wetting, reducing its free energy.
- Negative Value: Matric potential is always negative (except in saturated soil, where it is nearly zero) because soil’s binding forces lower water’s energy compared to free water.
Role in Water Retention & Movement
a. Wet Soil:
- Water held in larger pores, less tightly bound.
- Higher (less negative) matric potential → higher free energy → greater water mobility.
b. Dry Soil:
- Water held in small pores/thin films, tightly bound to soil.
- Lower (more negative) matric potential → lower free energy → restricted movement.
c. Water Movement:
- Flows from wet soil (high matric potential, less negative) to dry soil (low matric potential, more negative).
- Driven by matric potential gradient, moving from large pores (moist) to small pores (dry).
Importance in Unsaturated Flow
- Unsaturated Flow: Slow but crucial for supplying water to plant roots in non-saturated soils.
- Key Influence: Determines water availability for plants, irrigation efficiency, and soil moisture dynamics.