Soil moisture(soil water)

• Soil moisture is the amount of water held by soil particles.
• two types of soil moisture

  1. Surface soil moisture
  2. Root zone moisture
• surface soil moisture - uppermost layer of soil, where evaporation occurs
• root zone moisture - below surface soil moisture, where plants absorb water from
• form of water

  1. gas- water vapor
  2. liquid- water
  3. solid- ice
• types of water

  1. gravitational
  2. capillary
  3. hydroscopic
• Gravitational water - water that flows downward under gravity to lower levels of soil
• Capillary water - water that moves upward through small spaces between soil particles due to capillarity
• characteristics of gravitational water

  1. found in macro pores
  2. can cause upland plants to wilt and die because gravitational force occupies air space which is necessary to supply oxygen to the roots
  3. unavailable to plants
  4. drains out of the soil after 2-3 days of irrigation or rainfall
• characteristics of capillary water

  1. found in micro pores
  2. available to plants because capillary forces are greater than the force of gravity
  3. held by cohesion which is the bond of two or more different molecules and adhesion which is the force of attraction between similar molecules
  4. amount of water held is a function of the pore size which means the magnitude of the pulling force increases as the soil dries out
• Hygroscopic water

  1. is tightly bound to soil by adhesion properties, which causes some water only to be consumed by the roots of plants.
  2. is not found only in pores but also on the surface of soil particles
  3. tightly held in soil particles
• hygroscopic water


   Water absorbed from the atmosphere and held very tightly by the soil particles