Soil Composition and Properties Quiz

Soil Science (LAT 406)

Pedology and Edaphology of soil have evolved over two centuries of scientific studies.
Pedology (scientific study of soil) considers soil as a natural entity, a biochemically weathered and synthesized product of nature.
Pedology deals with aspects such as soil origin, classification, and description.
A pedologist views soil as the natural product formed from weathered rock by climate and living organisms.
Edaphology (study of soil from the standpoint of higher plants) conceptually views soil as a natural habitat for plants.
Edaphology considers soil properties in relation to plant growth and production.
An edaphologist may define soil as a mixture of mineral and organic matter capable of supporting plant life.
The word "soil" comes from the Latin word "solum," meaning floor. The French word "sol" and the Spanish word "suelo" are still used to mean either soil or floor.
Soil (general definition) is the naturally occurring, unconsolidated, or loose covering of weathered/broken rock particles and decaying organic matter (humus) on the surface of the earth, capable of supporting life. Also, soil is the part of the Earth's surface consisting of humus and disintegrated rock.
Generally, soil is an unconsolidated or loose combination of inorganic and organic materials supporting life.
The inorganic components of soil are primarily products of rocks and minerals gradually broken down by weathering and other natural processes.
Organic materials in soil are composed of debris from plants and the decomposition of tiny life forms in the soil.
There's a distinction between soil and land; soil is the synthesized product of weathered rocks and organic matter during decomposition. Land includes all aspects of the physical environment, of which soil is only one component.
Other factors influencing soil include underlying geology, hydrology, relief/topography, plant and animal population, and human activities (past and present).
Earth, one of eight planets in the universe, is composed of concentric layers of geochemically and geophysically different materials, including water and landmasses.
A well-formed soil includes organic materials (in various stages of decomposition, including humus), mineral/inorganic particles, air, and water.
The four components are intimately mixed in the soil.
The organic matter portion of soil is roughly half dead remains in various decomposition stages, and half alive. The living organisms in the organic part include plant roots, bacteria, earthworms, algae, fungi, nematodes, actinomycetes, and other similar lifeforms.
Mineral particles in soil are sorted by size: clay (<0.002 mm), silt (0.002-0.02 mm), and sand (0.02-2.00 mm).
The optimum volume composition of soil for crop growth is approximately 45% mineral matter, 5% organic matter, 25% soil water, and 25% soil air. These percentages are about the appropriate amounts of the four components for soil.
A soil has three phases: solid (mineral and organic matter), liquid (water containing dissolved salts and gases), and gas (various gases).
Morphological properties (physical properties) of soil can be observed via sight and feel.
Analytical properties (chemical properties) of soil can be divided into chemical and biological properties.
Soil properties include physical (mechanical), chemical, and biological properties.
Physical properties are the soil's characteristics that can be seen with the eye or felt with the thumb and fingers; they are a result of the interactions between parent materials, climate factors (like rainfall and temperature), topography (slope and direction), and lifetime effects of organisms living on or in the soil.
Changes to any of those factors usually mean a change in the type of soil formed.
Physical properties influence soil use, plant support, root penetration, drainage, aeration, moisture retention, and plant nutrients.
Physical properties depend on soil size, shape, arrangement, mineral composition, nature, amount and decomposition of organic matter in the soil, pore-space volume and form between soil particles, and the relative amounts of air and water in the pore space.
Important physical properties of soil include soil color, texture, structure, density, porosity, consistence, and temperature.

Soil Color

Soil color is frequently one of the first characteristics noticed.
Soil color indicates important soil conditions.
General soil color is determined by organic matter content, drainage conditions, and the degree of oxidation (or extent of weathering). Color is of no direct agricultural significance but an important criterion used to describe and classify soils.
Inherited soil color (lithochromatic) is determined by the parent rock material, for example, red soils often originate from red sandstones.
Acquired or pedochromatic soil color results from soil-forming processes.
Light colors often mean lower organic matter; dark colors often mean higher organic matter. Light or pale surface soil colors often mean that the soil is coarse textured, highly leached, and has high annual temperatures; dark colors sometimes indicate a high water table (e.g., poor drainage), low annual temperatures, and slow oxidation of organic materials. The color of the parent material can also affect color.
Shades of red or yellow with fine soil textures can indicate subsoil material incorporation into the surface layer.
Red, reddish-yellow, and yellow colors are due mainly to iron products in the clay fraction.

Soil Texture

Soil texture refers to the relative proportion/amount of different-sized mineral particles in a soil sample.
Soil texture is also described by the fineness/coarseness of mineral particles.
Soil texture depends on the proportions of sand, silt, and clay.
Each textural class has a range of possible amounts of sand, silt, and clay.
Soil separation systems (e.g., USDA, English, and International) exist for classifying soil based on the diameter range of particles.
Soil textures range from coarse to fine.

Soil Separates

Mineral particles fall into different size categories; names and size limits differ depending on the specific system being used (e.g., USDA).
Soil separation classifications exist (e.g., very coarse sand, coarse sand, fine sand, very fine sand, and clay).

Soil Texture Triangle

The textural triangle is a diagram showing how twelve soil textures are classified based on sand, silt, and clay content.
To identify the soil texture using the triangle, use the percentages of sand, silt, and clay in a given sample.
Steps to identify soil texture using the triangle:
Find the percent of clay on the left side of the triangle.
Find the percent of silt on the right side of the triangle.
Find the percent of sand percentage at the bottom of the triangle.
Connect the lines of the percentages. The point where all three lines intersect will represent the soil texture.

Determining Soil Texture

Soil texture can be determined in the field by rubbing moist-to-wet soil between the thumb and fingers.
In the lab, mechanical analysis separates soil particles into clay, silt, and different types of sands.
Organic matter is not part of the texture determination.

Soil Structure

Soil structure is distinct from soil texture; it refers to the way soil separates are put together.
Soil structure is the arrangement or combination of soil particles in crumb, granule, or other patterns; it's also the clumping of sand, silt, and clay into secondary clusters.
The primary particles (sand, silt, clay) are frequently grouped together to form aggregates. Natural soil aggregates are called peds, and those created by human activity are called clods.
Soil structure is studied in the field under natural conditions and described by Type, Class, and Grade.
Types of structural shapes include granular, blocky, prismatic, columnar, and platy. Other soil structural types are structureless (single-grained or massive).

Soil Drainage

Soil drainage is the rate and extent of water movement (across and down) in the soil.
Slope is an important factor in soil drainage; other factors include texture, structure, and the physical condition of the surface and subsoil layers.
Soil color can be a key indicator: clear or bright colors suggest well-drained soil; mixed, drab, or gray often indicates poor drainage.
Low-lying areas with run-off water and hardpan layers generally worsen internal drainage.
Sufficient water is needed; too little means the plants wilt and die. Too much water causes plant roots to suffocate, due to lack of oxygen. The ideal situation is one in which approximately half the pore space is filled with water.
A way to check drainage is to dig a hole the size of a 5-gallon bucket. Fill it, let it drain, repeat, and see how long it takes to drain.

Soil Depth

Effective soil depth is the vertical distance from the surface to the depth where plant root growth stops.
The barrier layer could be of rock, sand, gravel, heavy clay, or a cemented layer (like caliche).
Terms like "very shallow," "shallow," "moderately deep," "deep," and "very deep" express effective soil depths.
Deep, well-drained soils with good texture and structure are suitable for most plants. Deeper soils hold more nutrients and water compared to shallow soils. Soil depth impacts crop yields, particularly for annual crops without irrigation.
Plants on shallow soils have less mechanical support.
Trees on shallow soils are more easily blown over by wind.

Soil Surface Features

Soils with lost surfaces (due to erosion) are harder to till and yield less.
Practices to compensate for surface loss include improved fertilization and soil management.
Increasing organic matter content helps eroded soils regain tillage characteristics, water-holding capacity, and nutrient capacity.
Erosion causes surface loss and can be from water or wind, or land leveling during home construction. Using soil amendments and organic fertilizers improves poor-quality subsoil soil.