Lecture15-17(2008)

Lecture15-17(2008) - SOIL WATER CONTENT BULK DENSITY AND...

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SOIL WATER CONTENT, BULK DENSITY AND POROSITY Soils are often described and classified by their structure and particle size. Bulk density and pore space or porosity provide a more useful physical description of soil. Soil bulk density is a measure of soil compaction and strength. Porosity also provides some estimate of compaction, and the maximum space available for water (at saturation) or air. Read : Chapter 1 (p. 12-17), and 6 (p. 93-105) — Introduction to Environmental Soil Ph ysics
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SOIL WATER CONTENT, BULK DENSITY AND POROSITY (cont.) Bulk Densit y ( D b ): The mass of dry soil (M s ) per unit bulk volume (V t ). D b = M s /V t V t = V s + V a + V w Air Soil Bulk S pecific Gravit y ( D sb ): The ratio of the D b of a soil to the mass of a unit volume of water ( D w ). D sb = D b / D w [NOTE: D w . 1 Mg/m 3 or 1,000 kg/m 3 ]
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Definition : The mass of dry soil (M s ) per unit volume of soil particles (solids) (V s ). D s = M s /V s The average D s of the solid phase in most mineral soils is about 2.65 Mg/m 3 (2,650 kg/ m 3 ). --NOTE : This is the same as the density of quartz, which is the dominant mineral in the sand fraction of most soils. The density of some aluminosilicate clay minerals is near 2.65 Mg/m 3 . The densities of iron oxides and carbonate minerals are higher. Particle Densit y ( D s ) Example: Mineral M g/m 3 Quartz 2.65 Kaolinite 2.62 Calcite 2.72 Gypsum 2.32 Pyrite 5.02 Hematite 5.20 Organic matter has a much lower D s than mineral solids. This accounts for the low D b in organic soils.
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f = V f /V t = (V a + V w )/(V s + V a + V w ) f = 1 - ( D b / D s ) f = 1 - V s /V t Porosit y (f)
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Soil Water Content Gravimetric ( 2
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This note was uploaded on 08/08/2008 for the course SS 322 taught by Professor Lowery during the Spring '08 term at University of Wisconsin.

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Lecture15-17(2008) - SOIL WATER CONTENT BULK DENSITY AND...

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