03 Lect 03 Soil water - Soil as a habitat for...

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Soil as a habitat for microorganisms Soil as a habitat for microorganisms 2) Soil water 2) Soil water Reading : Textbook Sylvia et al., 2004. Chapter 2, pages 41-45 Article from Or et al., 2007. Sections 4 and 4.1, pages 1515-1518 I. Importance of water for organisms living in soils II. Properties of water 1. Cohesion and adhesion 2. Capillarity III. Soil water potentials 1. Matric, gravitational and osmotic potentials 2. Concepts of field capacity and permanent wilting point IV. Soil water content V. How do organisms access nutrients in soil solution? VI. What happen to soil microoorganisms as soil dries? 1. Effect on access to nutrients 2. Effect on mobility and growth 3. Limited interactions 4. Effect on cell hydration and resistance to water stress Essential to life Controls soil aeration and temperature Solvent Transport agent (nutrients, contaminants…) Participates in soil erosion Importance of water in soils
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Adhesion Attraction of water to mineral surfaces - Si O O <<< Cohesion Attraction of water molecules to each other - - Together, the forces of cohesion and adhesion make it possible for the soil solids to retain water and control its movement Water film on soil particles
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Capillarity Caused by adhesion and surface tension (cohesion) Force which lifts water above free surface against the force of gravity ¬ Stronger capillarity in smaller pores 0.15 (cm 2 ) h = r (cm) Diameter of the tube determines the height of capillary rise Capillarity h h - Macropores : water cannot be held
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03 Lect 03 Soil water - Soil as a habitat for...

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