Lecture43-52(2008)

# Lecture43-52(2008) - SOIL TEMPERATURE AND HEAT FLOW IN SOIL...

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SOIL TEMPERATURE AND HEAT FLOW IN SOIL Chapter 12 in Introduction to Environmental Soil Ph ysics Soil temperature governs many soil physical and biological processes Soil temperature is a function of radiant, thermal and latent energy processes

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Equations of Mass Movement in Soil Quantity = constant x driving force Water Solute Heat dX d A K Q Ψ = ) ( θ dX dC DA Q = dX dT A K Q t =
Soil temperature affects the rate of chemical and biological activity in soils—especially seed germination and plant growth. Soil temperature critical to conservation tillage, i.e., no-tillage has significant crop residue on the soil surface that modify soil temperature. Heat flow into and out of the soil takes place at the soil surface. Practices that cover soil e.g., grass/sod, conservation tillage with crop residue on the soil surface--alters this exchange of heat because any cover will have a lower heat conducting property than bare soil. Room at given temperature –carpet vs. tile floor which is colder? --Why?

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Room at given temperature –carpet vs. tile floor which is colder? --Why? q h = K t ( ΔT/Δ Z) It is K t Δ T/ Δ Z is a constant but K t is not

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Surface Energy Balance Day Night Evaporation Radiation Radiation Evaporation/ Condensation Convection Convection Convection Convection
Soil temperature :-- determined by transport processes for heat to and within the soil. Heat transport processes: 1. Radiation 2. Conduction 3. Convection 4. Latent heat transfer Radiation --transfer of thermal energy from a mass by electromagnetic waves. Both convection and conduction of heat require molecules to transfer heat. Radiative heat exchange requires no molecules to transfer heat from one surface to another. Radiant energy is given off by all objects. Both the sun and earth emit radiation but because the sun is hotter (at a higher temperature), the radiant energy is greater for the sun's surface than for the earth's surface.

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1. Radiation 2. Conduction 3. Convection 4. Latent heat transfer Conduction -- occurs by transmission of thermal energy of motion from one particle (microscopic size) to another. Convection
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Lecture43-52(2008) - SOIL TEMPERATURE AND HEAT FLOW IN SOIL...

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