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T9+Slides

# T9+Slides - Soil Water Soil Water Content Mass Basis Pw...

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1 Soil Water Soil Water Content • Mass Basis Pw (%) = ( Mass H 2 O / mass of dry soil) * 100 Usually grams of water per 100 grams of soil ) ( soil dry of mass soil wet of mass water of mass 100 * ) 24 105 ( (%) 0 hrs C soil dry of mass soil dry of mass soil wet of mass Pw Soil Water Content • Volume Basis – Pv (%) = (Volume of H 2 O / volume of soil) * 100 • Usually cm 3 of water per 100 cm 3 of soil Density of water: 1 gram of water = 1 cm 3 of water Conversions between volume and mass measures of soil water content • Since the density of water is 1 g/cm 3 , the mass and volume of water can be used interchangeably; also need bulk density (Db). Db Pw Pv * (%) (%) Db soil of mass O H cm g O H g mass Db soil of mass O H cm g O H g mass Pv * ) / 1 /( ) ( 100 / ) / 1 /( ) ( 100 2 3 2 2 3 2 density mass volume volume mass D & 100 * / / 100 (%) 2 2 3 2 3 soil density soil mass O H density O H of mass soil cm O H cm Pv Db Pw Pv * (%) (%) Important Concepts Water moves due to differences in the energy level of water between two points The speed of water movement is a function of the hydraulic conductivity Structure and Properties of Water •H 2 O = large anion O 2- and two small cations H + O H H δ positive δ negative Water molecule Bond angle 104.5 o

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2 δ = slightly δ positive δ negative δ positive δ negative Hydrogen bonding Water structure and polarity OH OH OH OH Water bound to the surface Hydroxyls at mineral surfaces Soil particle Soil particle H 2 OH 2 O Strongly structured water Low potential to do work Retained against gravity forces “Normal” water Not effected by the soil particles Free to move with gravity Soil particle Continuum in increased energy Adhesion to the soil/glass and cohesion between water molecules results in a net upward force next to the interface.
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T9+Slides - Soil Water Soil Water Content Mass Basis Pw...

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