# lab 5 – soil physics

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Lab 5 – Soil Physics . 1. Mechanical Analysis: Textural Class in the Lab %Sand , Silt, and Clay 2. Bulk Density: 3 Methods 3. Aggregation: Wet-Stability of Soil Aggregates 4. Particle Density and Sand Mineralogy. Mechanical Analysis. Soil Textural Class - Laboratory Method - PowerPoint PPT Presentation

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Today Sept. 17 2009

Lab 5 Soil Physics

1. Mechanical Analysis: Textural Class in the Lab %Sand, Silt, and Clay2. Bulk Density: 3 Methods3. Aggregation: Wet-Stability of Soil Aggregates4. Particle Density and Sand Mineralogy

Mechanical AnalysisSoil Textural Class - Laboratory MethodSoil Particles dispersed in 1 L H2O to separateStokes Law determines suspended particlesHydrometer measures suspended particles (g/L)Mechanical Analysis50 g soiladdedSandSiltClayDispersedParticlesMechanical Analysis50 g soiladdedSandSiltClayAfter 40 secSilt + Clayin suspensionMechanical Analysis50 g soiladdedSandSiltClayAfter 8 hoursClay onlyin suspensionMechanical AnalysisStokes Law (simplified):v = 8950r^2 Where r = particle radius, v = settling velocitySince r^2 (r squared), as r , v exponentiallyi.e. Sand settles quickly, Clay settles extremely slowlyCalculating Particle Size40 second reading:Gives si + cl = 20 gSince sa + si + cl = 50 gSa = 50 (si+cl) = 50 20 = 30 gSo % sa = 30/50 x 100 = 60%2 hour reading Gives suspended clay = 6 gSo, % cl = 6g/50g x 100 = 12%Since %sa + %si + %clay = 100%% si = 100% - %sa - %cl = 100 60 12 = 28%

Bulk density and Porosity Bulk Density: g/cm3Inversely related to porosityPorosity: % pore space (non-solid)Non-solid = macro/micro-pores filled with air and/or water %Porosity=100 x (1-BD/PD)Bulk density and Porosity Three Methods:1. Cylinder best for tilled soils; subjective volume2. Ring in situ method; retains soil structure 3. Clod plastic coated clod; allows for irregular shapes

Archimedes Principle

The Crown of Syracuse

https://www.youtube.com/watch?v=wEvtahSn_msAggregate Stability Wet-Sieving Soil Aggregates: How erodible?Stability: humus, macro-pores, rootsSlaking: aggregate breakdown due to rapid wetting%WSA (Water Stable Aggregates):Proportion of retained (wet-stable) aggregatesSand Mineralogy DisplayTwo sands; one dark, one light-coloredWhy?Particle DensityBlack mineral, white mineral: what are they?

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