Soil Water

1
Soil Water

• Chapter 5

2
Chapter 5 Outline

• I. General Properties of Water
• II. Capillary Action
• III. Energy Concepts
• IV. Flow of Water
• V. Specific Examples

3
Michael J. Singer and Donald N. MunnsSoils An
Introduction, 6e
4
What makes H2O so amazing?

• I. General Properties of Water
• A. Polarity
• B. Hydrogen Bonding
• C. Cohesion/Adhesion
• D. Surface Tension

5

• I. General Properties of Water
• II. Capillary Action
• A. Equation
• B. Comparison of textures
• III. Energy Concepts
• IV. Flow of Water
• V. Specific Examples

6
Capillary Action h0.15/r

• In moist soils, the pores act like thin tubes,
  and water is held by capillarity. Pores are not
  straight and smooth like the tubes in the figure,
  and so water does not reach the same height in
  pores as it would in tubes of the same diameter.
  A soil with many small pores holds more water by
  capillarity than does a soil with few large
  pores. In addition, because of capillarity, water
  rises higher from a water table in a clay soil
  than in a sandy soil.

Figure 5.6
7

• I. General Properties of Water
• II. Capillary Action
• III. Energy Concepts
• A. Energy review
• B. Potential
• C. General Equation and terms
• 1. Gravitational potential
• 2. Osmotic potential
• 3. Pressure potential (matric and hydrostatic)
• D. Measuring water content (?) and potential
  (?)
• IV. Flow of Water
• V. Specific Examples

8

• A. Energy Review
• 1. kinetic vs potential energy
• 2. movement from high to low energy
• B. Potential
• 1. difference in energy level of water from one
  site to another
• 2. wet soil most water far from soil particle
  surface (loosely held, high ?)
• 3. dry soil most water located in small pores
  (tightly held, low ?)
• Water potential is a measure of the water's
  availability, or escaping tendency, or tendency
  to move. It is measured relative to water at a
  standard pressure and temperature at some
  reference elevation.
• High water potential means that water can easily
  move. It is loosely held.
• Water potential is high when it is zero and low
  when it is -1500 kPa.
• More negative is lower potential.

9

• ?t ?g ?m ?o ?s .
• ?ggravitationalpulls water downward
• always positive
• ?mmatricattraction to solids (suction, tension)
• adhesion and capillary (movement moist high
  to dry low)
• ?oosmotic attraction to ions (lower potential
  energy)
• gtconcentration lt potential (impt for water
  uptake by plant)
• ?ssubmergencehydrostatic (saturated zones only)

10

• What are the major components of water potential?
  What factors most influence water potential in
  soil?
• The major components of water potential are the
  gravitational, osmotic, and matric potentials.
• Dry Soils
• In unsaturated soils, matric and osmostic
  potentials are dominant and decline respectively
  with decreasing water content or increasing
  salinity.
• Wet Soils
• In saturated soils and aquifers, gravitational
  potentials are dominant.

11
Table 5.1
12
(No Transcript)
13

• D. Measuring water content (?) and potential (?)
• How would you measure the water content and the
  water potential of a soil?
• Water content (?) of soil is most easily measured
  by weighing a sample wet and again after drying
  (oven to constant weight). Water content
  weight loss/dry weight.
• Water potentials (?) in soil materials can be
  measured with tensiometers.

14
Water content calculation