Lecture 3 Texture - Characterizing Soil Horizons Characterizing Physical Properties of Soils Idealized Surface Soil Voids Avenues Storage

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Unformatted text preview: Characterizing Soil Horizons Characterizing Physical Properties of Soils Idealized Surface Soil Voids Avenues Storage Distribution Movement Solids Interactive Media Minerals Organic matter Reactivity Parent Material to Soil Differentiation Additions Losses Parent Material Translocations Transformations Bedrock Bedrock Soil Horizons Roughly parallel layers in the soil with varying composition and properties Criteria for Characterizing Soil Horizons Soil Color Texture Density Structure Organic matter Mineralogy Chemistry Soil Color Hue dominant spectral color; related to the wavelength of light. Related to the proportions of red to yellow. Value related to total amount of light reflected. Chroma measure of the strength of spectral color Hue = 10 YR Value = 6 Chroma = 3 Munsell Color 10 YR 6/3 Physical Criteria for Delineating Horizons Physical Color Texture Structure Density The Soil Mineral Component: Texture the size of soil particles Soil texture refers to the relative amounts of three distinct size separates comprising the soil mineral component. Sizes classes of particles Sand Silt Clay Soil Texture Soil Class Sand Silt Clay Diameter Dominant Minerals (2.0 – 0.05 mm) Quartz (0.05 – 0.002 mm) Quartz /Feldspars/mica (<0.002 mm) Secondary minerals Quartz Distribution clay silt sand 100% Importance of Soil Texture (Distribution of particle sizes) Soil Porosity Particle Surface Area Water/Gas Movement Reactivity Soil Porosity Porosity – the total volume of soil pores - the distribution of pore sizes Sand Silt Clay Texture, Pore Sizes, and Water Large particles yield large pore spaces Small particles yield small pore spaces Water moves rapidly and is poorly retained in Coarse-textured sandy soils. Water moves slowly and is strongly retained in Fine-textured, clayey soils. Sands Rapid Poor Retention Clays/iron Slow Water Retained Surface Area and Particle Size 2 mm 2 mm 1 mm 1 mm 1 mm 2 mm If each of the resulting cubes was divided similarly, the surface area would increase 16 times more Surface Area Surface units Specific Surface Area = Surface Area cm2 g mass water nutrients Interface with the environment O.M. gasses microorganisms Specific Surface Area Separate SSA (cm2/g) Sand 30 Silt 1500 Clay 16 g of clay 3,000,000 100 g soil Soil A 95 g sand 4 g silt 1 g clay Soil B 90 g sand 5 g silt 5 g clay 95 g sand x 30 g/cm2 = 2850 cm2 90 g sand x 30 g/cm2 = 2700 cm2 4 g silt x 1500 g/cm2 = 6000 cm2 5 g silt x 1500 g/cm2 = 7500 cm2 1 g clay x 3 M g/cm2 = 3 M cm2 Total = 3,008,850 cm2 5 g clay x 3 M g/cm2 = 15 M cm2 Total = 15,010,200 cm2 Soil Horizons Texture Clay Content Surface Area Potential Reactivity Soil Textural Classes Soil Textural Triangle Florida Soils clay Sand Loamy sand Sandy loam Sandy clay loam Sandy clay Clay <10% 10 – 15% 15 – 20% 20 – 35% 35 – 55% > 50% 70% sand, 20% silt, 10% clay 60% sand, 10% silt, 30% clay Measuring Soil Texture Texture-by-Feel Relative amounts of 3 soil separates: Sand, Silt, and Clay Gritty smooth plastic Texture-by-Feel Soil Field Analysis No Ball Sand No Ribbon Loamy Sand Increasing Ribbon Length Low Clay Medium Clay High Clay Grittiness, Smoothness Texture by Feel Sand = Gritty Silt = Smooth Clay = Sticky, Plastic Laboratory Analysis of Soil Texture Laboratory Analysis Laboratory Sedimentation – Sand, Silt, and Clay Fraction drag drag gravity Sedimentation Sand Sand Silt Silt Clay Clay silt sand Quantifying Sedimentation Rates Stokes’ Law Stokes’ g (dp-dL) D2 Velocity V(cm/s) = 18ų g = gravity dp = density of the particle dL = density of the liquid ų = viscosity of the liquid V = K D2 K = 11,241 cm-1 sec-1 1 cm · sec Stokes’ Law V = K D2 K = 11,241 cm-1 sec-1 Sand: D = 1 mm 0.1 cm V = 11,241 x (0.1)2 1 cm · sec X cm2 = 112.4 cm/sec Stokes’ Law V = K D2 K = 11,241 cm-1 sec-1 clay: D = 0.002 mm 0.0002 cm V = 11,241 x (0.0002)2 1 cm · sec X cm2 = 0.00045 cm/sec Settling Velocity (cm/sec) 500 450 400 350 300 250 200 150 100 50 0 clay 0 0.5 silt sand 1 1.5 Particle Diameter (mm) 2 2.5 Sedimentation Sedimentation The density of a soil suspension decreases as particles settle out. 1 minute Sand settles out 4 hours Silt settles out suspension 1 min. silt sand 4 hr. Hydrometer Method Stem 0 g/L Scale Bulb weight hydrometer t=0 Pure distilled water (18o C) = 0 g/L t = 1 min Hydrometer Method Hydrometer Add 40 g soil to 1 liter of water Time = 0 sec density = 40 g/L Time = 1 min. density = 10 g/L Sand settled = 40 g– 10 g= 30 g Sand (%) = 30 g sand = 0.75 = 75% 40 g soil Hydrometer Method Time = 4 hrs density = 4 g/L What is being measured? Clay content = 4 g Clay % = 4 g clay = 0.10 = 10% 40 g soil Silt % = 100% - (75% + 10%) 100% - 85% = 15 % Hydrometer Method Sand = 75% Silt = 15% Clay = 10% Sandy Loam Reactivity, Water Movement Next: Density, Structure, Porosity ...
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This note was uploaded on 07/31/2011 for the course SOS 3022 taught by Professor Staff during the Fall '08 term at University of Florida.

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