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Lecture 7a Soil Water - Part 1

Lecture 7a Soil Water - Part 1. Water Storage for a Thirsty Planet – more crop per drop and more drink per glass. Describe in your own words what happens to the water in the diagram below as it is added to a dry soil. How does the water enter and move through the soil?. Water.

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Lecture 7a Soil Water - Part 1

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  1. Lecture 7aSoil Water - Part 1 • Water Storage for a Thirsty Planet – • more crop per drop and more drink per glass.

  2. Describe in your own words what happens to the water in the diagram below as it is added to a dry soil. How does the water enter and move through the soil? Water A horizon - Air Dry Soil

  3. Soil Water Adhesion Water- water attracted to solid surfaces • held by strong electrical forces - low energy • little movement- held tight by soil • exists as a film • unavailable to plants • removed from soil by drying in an oven

  4. Soil Water Cohesion water – water attracted to other water molecules • held by hydrogen bonding (–when + & - of water molecules are close together)=……… • liquid state in water film • major source of water for plants • greater energy than adhesion water

  5. Gravitational Water • exists in macro -pores • has greatest energy (true liquid) • moves freely due to gravitational forces. (2 hands, 1 hand, 3 fingers, 1 finger, touch) Adhesion Cohesion Gravitational Soil

  6. Soil Water = Soil Moisture • Water has energy - substances tend to change from a state of high energy to states of low energy (water runs down hill) Soil water potential - water is held in soil by “tension” or attraction of water molecules to solid surfaces and to other water molecules

  7. Water Potential • Tension = - pressure • Soil water potential = amount of work that must be done per unit quantity of water in order to transport a quantity of water from a pool of pure water to the soil water.

  8. Soil water potential • Total soil water potential = Matric potential + gravitational potential + Osmotic (salts) • As the soil dries the matric potential decreases or a larger negative number • 00 -5 -8 -10 -15 -55 -100 • sat. wet - -------- dry------- > very dry

  9. Water tension (+) or Potential (-) 0 bar -.33 bar • 1 bar • -15 bar

  10. Soil Water Classification- a way to quantitatively describe the water in the soil. • 0 to -0.3 bar = Gravitational (not available) • -0.3 = Field Capacity • -15 bar = wilt point • Between -0.3 & -15 is plant available water (AWC) • -15 to -100 bar = stages of air dry • -10,000 bar = oven dry AWC 0 bar -0.33 -15 -100 -10000 Saturated Field Cap Wilt point air dry oven dry

  11. Water moves from areas of high potential (wet soil : -2 or -4) to areas of low potential (dry soil -8) -.4 -3 -7 -8 -2 Root Soil Soil

  12. The End – Part 1

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