Soil Water Reservoir Properties

Soil as a Water Reservoir

• Soil holds water molecules through adhesion, cohesion, and surface tension.
• Water-holding capacity depends on soil texture, structure, and organic matter content.
• Sandy soils have large pores, drain quickly, and have low water-holding capacity.
• Clay soils have smaller pores, drain slowly, and can store more water.

Soil Water Potential

• Soil water potential is the energy required to remove water from the soil.
• Measured in units of joules per kilogram (J/kg) or kilopascals (kPa).
• Water is held in place by forces including gravity, adhesion, and cohesion.

Water Movement in Soil

• Water moves from areas of high water potential to areas of low water potential.
• Two types of water movement:
  • Mass flow: Water moves through pores and cracks driven by gravity.
  • Diffusion: Water molecules move randomly from areas of high concentration to low concentration.

Soil-Water-Plant Relationship

• Soil-water-plant relationship defines the dynamic interactions between soil, water, and plants.
• Ensures the transfer of nutrients, water, and support vital for plant life.

Water: The Essence of Life for Plants

• Water is a fundamental component of plant life, making up 70-80% of plant weight.
• Water serves as a universal solvent, facilitating transport of nutrients and metabolites.
• Water is essential for photosynthesis, maintaining cell turgidity, and providing structural support.

Water Availability for Plants

• Plants can only uptake water from the soil if soil water potential is above a certain threshold value.
• Different plant species have different threshold values.
• When soil water potential drops below the threshold, plants experience water stress.

Functions of Water in Plants

• Water is essential for seed germination and plant growth.
• Water forms over 90% of the plant body by green or fresh weight basis.
• Water is necessary for photosynthesis, as a solvent for fertilizers, and for transporting chemicals.
• Water pressure in plant cells provides firmness to the plants.
• Water is essential for transpiration and aquatic life.

Soil's water-holding capacity depends on its texture, structure, and organic matter content. Learn about the forces that help soil retain water and how different soil types vary in their water-holding capacity.