Soil Water

Soil Water - 1 Soil Water SS 121 (Chapters 5 & 6) 2 3 4...

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1 1 Soil Water SS 121 (Chapters 5 & 6) 2 Hydrologic cycle 3 4 Water held in the soil by • Adhesion and Cohesion – The water molecule – Surface tension – Capillarity 5 6 Adhesion and cohesion 7 Soil water potential energy • How hard do plants have to work to get water out of soil? • Potential energy of soil water as a result of forces acting on the water • Strongest and most common forces: adhesion+cohesion (matric), dissolved salts • Pressure units: atmospheres (atm), bars, kilopascals (kPa) 8 Soil water potential For MOST soils: φ t = φ m + φ o Total soil water potential = matric potential + osmotic potential Matric potential, φ m 0 φ ο always 0 Most soils: φ t = φ m Salty soils : φ t = φ m + φ o 9 Water Content Gravimetric Volumetric Depth ratio 10 Water content • Gravimetric water content
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2 By mass θ m = (Mass moist soil-Mass OD soil) Mass OD soil • Volumetric water content By volume θ v = θ mx Db Dw • Depth ratio Depth of water per depth of soil d water = θ vx ±d soil 11 Suppose you have a soil, sampled moist, volume = 100 cm 3 . Moist weight is 156 grams. Oven dry weight is 130 grams. What is the gravimetric water content?
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Soil Water - 1 Soil Water SS 121 (Chapters 5 & 6) 2 3 4...

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