Chapter 4 - Soil Architecture and Physical Properties

Munsell Color System

A color system used to classify and describe the color of soil based on hue, value, and chroma, facilitating the identification of soil characteristics and properties.

Organic matter color

dark brown to black

Wet soil color

darker in color than dry ones

Soil separates classification

Classification system based on particle size, including sand, silt, and clay.

Specific Surface Area

the surface area for a given volume or mass of particles

Colloids

tiny particles that remain suspended in soil water and have high surface area and reactivity.

4 fundamental surface phenomena

1 - Water is retained in soils as thin files on the surface of soil particles

2 - both gasses and dissolved chemicals are attracted to and absorbed by mineral particle surfaces

3 - Weathering takes place at t he surface of mineral particles

4 - The surface of mineral particles often carry both negative and some positive, attracting themselves to another

5 - Microorganisms tend to grow and colonize particle surfaces

Micropores

Typically filled with water

Slow water and gas movement

Smaller than 0.08 MM

Macropores

Allow ready movement of air and drainage of soil

large enough to accommodate roots and tiny animals

Larger than 0.08 MM

Textual classes

-12 major classes in a triangle

-Range in percentages of sand, silt, and clay

Loam

mixture of sand, silt, and clay that exhibits the properties of 3 components equally

-Not equal amounts

-Contains many sub divisions

Sandy Loam

Mixture of sand, silt, and clay where sand is dominant

Pebbles/gravel

2.0 - 7.5 MM

Cobbles

75 - 250 MM

-Rond

Flags

75 - 250 MM

-flat

Stones/boulders

250 MM +

Structure

arrangement of primary soul particles into groupings called aggregates or peds

Particle Density

Mass of soil minus air, water spaces per unit volume of soil.

Bulk Density

Mass of dry soil per unit volume, including air and water spaces

lower

fine-textured soils such as silt loams, clays, and clay loams generally have HIGHER/LOWER BD than sandy soils

higher

deeper in the soil profile BD are generally HIGHER/LOWER

The surface horizons of most forested land have HIGHER/LOWER BD

20 to 40

Conventional timber harvest generally disturbs and compacts (__ to ___) precent of the forest floor

Plow Pans

high bulk density immediately below the plowed layer

Subsoiling

a cultivation practice used to break up compacted layers of soil beneath the surface, improving water infiltration and root growth.

Soil Strength

the property of soil that causes it to resist deformation

higher

The lower the BD the HIGHER/LOWER the precent pore space (total porosity)

granulatiobn

the process of forming soil aggregates or clumps, which affects soil structure and porosity.

Flocculation

the process by which soil particles aggregate into larger clumps or flakes, enhancing soil structure and water retention.

Microaggregates

Clumps of soil particles smaller than 0.03 MMthat contribute to soil stability and improve water retention. ps

pseudosand

Soil texture that resembles sand but is composed of smaller particles or aggregates, often improving drainage and root penetration.

physical chemical aggregation

Most important _______ processes are:

1 - the mutual attraction among clay particles

2 - The swelling and shrinking of clay masses

biological aggregation

most important ____ processes are:

1 - burrowing and molding of earthworms

2 - the enmeshment of particles by sticky networks of roots and fungal hyphae

3 - the production of organic glues by microorganisms such as bacteria and fungi.

macroaggregates

larger clumps of soil particles that improve soil structure and enhance aeration and water infiltration.

glomalin

gooey sugar-protein provided by fungi

very effective as a cementing agent

Surface seal

falling water creates a crust on the soil surface that can restrict infiltration and promote runoff.

Soil consistence

the resistance of soil to mechanical stress or manipulation at various moisture contents and its ability to maintain shape when disturbed.

Collapsible soils

noncohesive materials in which loosely packed sand are cemented by moisture and lose strength when wet.

Thixotropy

the sudden assumption of liquid properties of a wet soil when subjected to vibrations