Exam Schedule Exam I: Friday, May 22 nd Exam II: Friday June 5 th Exam III: Friday June 19 th Review sessions will be on the Thursday preceding the exam.

Soil Texture Three separates: Sand, Silt, Clay Importance: indicator of pore size, surface area, water movement, reactivity There are 12 textural classes based on relative abundance of sand, silt, clay Florida soils tend to range from sandy to sandy clay textures Texture-by-feel assesses grittiness, smoothness, plasticity to estimate texture Laboratory analysis relies on sedimentation of soil particles in water Stokes’ Law determines the settling rates of particles from water Large particles (sand) settle quickly, small particles slowly. A hydrometer measures the density of a soil suspension Based on the density, the mass of particles remaining suspended is determined

Particle Size Large/coarseMedium Fine/Small Sand Loamy Sand Sandy Loam Sandy clay Loam Silty clay Loam Silt Loam Loam Clay Loam Sandy Clay Silty Clay Clay Pore Size Large Medium Small Reactivity WeakModerate Strong Texture

Texture and Civilization?

Tigris-Euphrates Nile Earliest Civilizations

Civilization Year-round supply of water Enduring Sunlight Trustworthy harvests Building materials Population increases Substantial homes Relative Safety, peace Neolithic Founder Crops Wheat Barley Flax Chick Pea Lentil cows, goats, sheep, and pigs Nile Jordan Tigris Euphrates Periodic Flooding

Flooding

Flooding and Soil Texture Sand mm Silt 0.05 – mm Clay < mm Clay

Sand1 mmV = 112 cm/sec Silt0.05 mmV = cm/sec Clay0.002 mmV = cm/sec Stokes’ Law: V = kD 2 K = 11,241 cm -1 sec -1

Flooding slows flow River channel Sedimentation Sand Clays/Silts

Flood peaks in mid-September Blue Nile The Nile Kenya Uganda Tanzania

Mesopotamia Euphrates Alluvial Plain Flood: March through June

Agriculture and Irrigation Irrigation Canals Dikes Weirs Reservoirs channels

History and Soil Texture (knowledge from clay and stone)

Stone and Clay Egypt Sumer Stone Clay

Architecture and Sculpture Egypt

The Language of Power sacred, ceremonial, literary, and scientific language Sumerian

Soil Structure, Density, Porosity

Soil Structure Arrangement or grouping of individual soil particles into secondary units.

Soil Structure Peds Aggregates Units of soil Structure

Chemical Processes – electrostatic attraction between clay particles and between organic particles. Biological Processes -macro-organisms (burrowing, tunneling,wastes) -roots, fungal hyphae (compression, fibers, exudates) -microorganisms (organic residues) Formation Soil Structure

Importance Effects on porosity, water retention, water movement Small pores Large pores Intra-aggregate pores Inter-aggregate pores (within) (between) Water moves easily and is poorly retained in inter-aggregate pores Water moves slowly and is strongly retained in intra-aggregate pores

Soil Structure is Desirable Poor soil structure can inhibit infiltration of water, water movement, growth of roots.

Structure is the arrangement or grouping of individual soil particles into larger secondary units. Clays and organic matter possess natural electrical Charge which can electrostatically bind particles together. Macro-organisms and microorganisms can aid in binding of individual particles into larger aggregates.. Aggregation allows for both movement and retention of water via macropores and micropores, respectively.. Poor soil structure can inhibit infiltration of water, water movement, growth of roots. Summary

Soil Density

Density Density = Mass Volume g cm 3 ( ) 2.65 g/cm 3

Soil Bulk Density Density of soil including the particles and the pore spaces x y z Volume = xyz B.D. ranges between 1.1 and 1.6 g/cm 3 (for mineral soil with 1 – 5% organic matter) BD = mass OD soil volume solids + pores

Bulk vs. Particle Density Bulk density measures the mass of the soil solids in relation to the volume of the soil solids and the soil pores. x y z Particle density = Mass of particle Volume of particle No pores Bulk density = mass solids volume xyz BD = 1.6 g/cm3 PD = 2.65 g/cm 3

Sampling for Density Known Volume

Dry and Weigh: mass/volume = Bulk Density

Factors Affecting Bulk Density organic matter aggregation arrangement of particles compaction depth in profile Porosity (pores are weightless)

Organic Matter Typical1-5% organic matter Mineral Soil: bulk density = 1.1 –1.6 g/cm 3 Organic Soils: > 20% organic matter bulk density = 0.1 – 0.6 g/cm 3 Factors Affecting Bulk Density

Aggregation One sand grain One aggregate of Clay sized particles (Zero porosity) (50% porosity) Aggregation generally increases overall porosity, decreases density

Packing Arrangement Discrete particle size classes Continuum of particle sizes Particle Size Arrangement (compaction) Sorting

Depth in Profile Lower organic matter Fewer roots Compaction from above => Higher bulk density Aggregation can mitigate Some of these effects.

Summary Bulk densities of typical mineral soils range between 1.0 and 1.6 g/cm 3. Organic matter increases porosity, decreases BD Organic soils can have BD as low as 0.1 g/cm 3. Compaction decreases porosity, increases BD Aggregation increases porosity, decreases BD Depth in profile decreases porosity, increases BD

Porosity

Bulk Density and Total Porosity Bulk Density (g/cm 3 ) 100% Porosity ) ( BD PD 1 - % Porosity = [ ] X g/cm 3 Bulk density high porosity low Bulk density low porosity high

AEBAEB BD = 1.1 g/cm 3 BD = 1.15 g/cm 3 BD = 1.6 g/cm 3 P = 59 % P = 57% P = 40 % Bulk Density and Porosity A E E B

Pore Size Distribution Macropores > 0.8 mm in diameter large, freely draining sands, inter-aggregate pores Micropores < 0.8 mm in diameter small, storage of water clays, intra-aggregate pores

The effect of total porosity and of pore size distribution is largely related to the movement and retention of water as well as the movement of soil gases Knowledge of texture, structure, bulk density, and porosity allow deduction of the patterns of movement of water and gases in soils Next: Water in Soils