Soils 205- General Soils

Lecture 8- Soil water

I. Description of soil water

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    a. Properties of water

        i.  polarity

        ii.  Hydrogen bonding

        iii.  Adhesion and cohesion

        iv. Surface tension

       v.  Capillarity

                -due to cohesion and adhesion

                - smaller pores hold water with greater energy

            capillary rise in soils

II.  Soil Water Energy- All substances, including water, have a tendency to move or change from a state of higher to one of lower energy.  Therefore, differences in energy level from one site to another influences water movement.  Potentials are used to describe the potential energy levels of water in soils.

    a.  Factors affecting the energy state of soil water

        i.  Matric forces

        Matric potential (y_m) -

        ii.  Osmotic forces

        Osmotic potential (Yo) -

        iii.  Gravitational forces

        Gravitational potential (Yg) -

        iv.  Soil water potential

             Total soil water potential = Yt = Yg + Yo + Ym

             Differences in potential cause gradients, and WATER FLOWS IN RESPONSE TO GRADIENTS.