Soil Science Spring 2017 Kaizad F. Patel Soil profile image credits: University of Idaho, Michigan State University, NRCS 1. Color 2. Texture 3. Density 4. Consistence 5. Atterberg Limits 6. Drainage 2 Outline
Value/Chroma dominant spectral color degree of darkness or lightness of the color strength/saturation of spectral color 14 Soil hues 10R 2.5YR 5YR 7.5YR 10YR 2.5Y 5Y red yellow
of Idaho - CALS 17 Soil Taxonomy Mollic epipedon Dominant color with chroma of 3 or less, moist Albic materials Color value of 3, moist Chroma of less than 2 Spodic materials Hue of 5YR or redder Color of 10YR 3/1 18 Bangor soil series A horizon has hue of 10YR to 5Y, value of 3 or 4, and chroma of 1 to 3. E horizon has hue of 10YR to 5Y, value of 5 or 6, and chroma of 0 to 2 Bs horizon has hue of 5YR to 10YR, value of 3 to 5, and chroma of 3 to 8. BC horizon has hue of 7.5YR to 5Y, value of 4 to 6, and chroma of 2 to 8 Image taken at Dwight B. DeMerritt Forest, ME
proportions of sand, silt, clay in a soil 21 mineral particles, <2.0 mm in equivalent diameter, ranging between specified size limits 22 Soil Separates
<2.0 mm in equivalent diameter, ranging between specified size limits 23 Soil Separates mm 2.0 - 1.0 1.0 - 0.5 0.5 - 0.25 0.25 - 0.10 0.10 - 0.05 Silt 0.05 - 0.002 Clay <0.002 SAND USDA Classification of Soil Separates Fine Sand Very Fine Sand Silt Clay Very Coarse Sand Coarse Sand Medium Sand Sand – gritty, low nutrient and water retention Silt – velvety, medium to low nutrient and water retention Clay – sticky and ribbons, high nutrient and moisture retention 24
<2.0 mm in equivalent diameter, ranging between specified size limits 25 Soil Separates does not include OM does not include coarse fraction > 2 mm = coarse fraction < 2 mm = fine fraction 26 Soil texture triangle
clay 20% silt 30% sand Total = 100% 28 Loam Exhibits properties of sand and clay in equal amounts Does this mean loam contains sand and clay in equal amounts?
influences specific surface area 31 Importance of soil texture 32 specific surface area surface area per unit mass units: m2/g Michael J. Singer and Donald N. Munns Soils: An Introduction, 6e smaller particles = greater specific surface area
surface area 1536 mm2 = 1181.5mm2/g 384 mm2 =295.4mm2/g Specific surface area and adsorption 34 adsorption vs. absorption greater surface area greater adsorptive capacity =
area and adsorption 35 H2 O water water retention? drainage? erosion? shrink-swell capacity? Specific surface area and adsorption 36 Ca+2 Na+ Mg+2 nutrients
2. Mechanical Analysis by Hydrometer Method 3. Mechanical Analysis by Pipette Method 41 Stokes’ Law 42 Stokes’ Law: settling velocity For a given solid in a given liquid V = kD2 V ∝ D2 Bigger particles settle out of suspension earlier. V = settling velocity g = gravitational acceleration ρp = density of particle ρf = density of fluid D = diameter of particle µ = viscosity of fluid Stoke’s Law V=g ρp −ρf D2 18µ
Law: settling velocity D 2D V 4V V ∝ D2 Solve: Radius 5 cm, velocity = V Radius 25 cm, velocity=? Coarse soil particles settle out first Hydrometer method Pipette method 44 Stokes’ Law Stoke’s Law V ∝ D2
silt 30 seconds 12 hours pipette hydrometer Transmission Electron Microscopy Scanning Electron Microscopy X-ray attenuation Particle counting (Coulter Counter) Light scattering 48 Modern techniques Electron Microscopy David J. Morgan, Wikimedia
aggregates single grained individual particles do not form aggregates massive the entire horizon appears cemented sandy soils Type Class Grade ped name size distinctness 60
(Strength/ firmness) Structureless Weak peds cannot be removed without being destroyed Moderate peds can be removed from the profile Strong peds, when removed, are rigid and durable in the hand Strong Prismatic John Kelley, Soil Science flickr 62
air circulation 63 Why is structure important? Colorado State University Biological factors Physico-chemical factors 64 Formation and stabilization of aggregates
flocculation cation bridging between clay platelets Calcium flocculant Sodium deflocculant, dispersant 70 Physico-chemical: cementation by OM aggregates fall apart aggregates are stable
tillage John Deere Tillage can promote or destroy aggregation. 72 Physico-chemical: tillage Tillage can promote or destroy aggregation. break large clods into aggregates incorporate OM into soil oxidative loss of OM (long term) crush and smear soil aggregates (if wet) puddled soil well-granulated soil
per unit volume of a substance ρ = mass volume density 74 rho g cm3 g/cm3 density of water = 1 g/cm3 at standard temperature and pressure 1 cm3 of water weighs 1 g density of 1 g water vs. 10 g water?
of soil particles divided by volume of the solid soil particles Mass of soil particles divided by bulk volume of soil Units? 76 Mass same Bulk volume greater Which type of density is greater?
of Location in profile surface bulk density? subsurface 84 Influence of land management no till BD decreases (short term) BD increases tilling compaction Long-term: loss of OM till BD increases
pore space 89 Soil A 2.5 Mg/m3 2 Mg/m3 Soil B 2.5 Mg/m3 1 Mg/m3 Which soil has higher porosity? Particle density Bulk density same mass lower bulk density = more volume more pore space Total Soil Porosity = 100−( Db Dp 100) 90 The densities of a soil are: 2 Mg/m3 1 Mg/m3 What is the porosity of the soil? 50%
with which soil can be reshaped or ruptured Amount of forced needed to crush a clod Manner in which soil responds to the force 93 Rupture resistance Stickiness Plasticity Penetration resistance 94
soil to withstand applied stress 95 Rupture resistance Loose Soft Slightly hard Hard Very hard Extremely hard 96 Dry soils Loose Very friable Friable Firm Extremely firm Slightly rigid Wet and moist soils Rupture resistance What kind of food do pedologists like? Anything, as long as its friable soil clod crumbles increasing force
elastic vs. plastic object is permanently deformed does not regain original shape when force is removed object is not permanently deformed regains original shape when force is removed Degree to which “puddled” or reworked soil can be permanently deformed without rupturing 100 Plasticity
to rupture Used by soil scientists Consistency Resistance to penetration Used by engineers 101 102 critical limits of water content in fine grained soil
drained 2. Somewhat excessively drained 3. Well Drained 4. Moderately Well Drained 5. Somewhat Poorly Drained 6. Poorly Drained 7. Very Poorly Drained 8. Subaqueous 107 Soil Drainage Classes water table upper surface of zone of saturation groundwater water within the saturated zone vadose zone unsaturated zone above the water table capillary fringe zone of wetting by capillary movement
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