Soils 205- General soils

Lecture 13- Soil temperature

I.  Soil temperature affects:

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    a.  control of soil temperature

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    b.  radiation balance

    c.  radiation balance- day and night

II.  Thermal properties of soils

    1) specific heat- the amount of energy required to raise the temperature of water by 1C.

                    Dry soil =

                    water =

    2)  Heat of vaporization-  It takes 540 kcal (2.3J) for every kg of water vaporized.  This energy must come from solar radiation or from the surrounding soil.

    3)  Thermal conductivity- heat flow is similar to water flow in that it is determined by a driving force and the ease with which heat flows in soils.

        a.  Thermal conductivity is influenced by:

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        Heat conduction provides a means of temperature adjustment.  Since it is slow, changes in subsoil temperature lag behind those of surface horizons.

III.  Soil temperature

        a.  Diurnal fluctuations

        b.  seasonal fluctuations

IV.  Soil temperature control

    1)  Soil cover- mulches or litter layers (Fig. 7.27 and 7.28)

    2)  moisture control