Chapter 1 - Soil Horizons, and Soil Water

These flashcards cover key vocabulary terms and concepts related to soil properties, characteristics, and functions, providing comprehensive study aids.

Sand

Soil particle size ranging from 2.00 to 0.05 mm, visible to the naked eye, feels coarse and gritty.

Silt

Soil particle size from 0.05 mm to 0.002 mm, not usually visible unaided, feels smooth when moistened.

Clay

Fine soil particle size less than 0.002 mm, only visible with electron microscope, feels very smooth or powdery.

Soil Texture

Describes the proportion of soil particle sizes that influence water holding capacity and aeration.

Sandy Textured Soils

Soils that exhibit little plasticity, cannot retain large amounts of water, and have large voids between pores.

Silty Textured Soils

Intermediate texture between sand and clay, retain large amounts of water with moderate to slow permeabilities.

Clay Textured Soils

Soils that exert a significant influence on chemical and physical properties; high in aggregation and water movement.

Volume Composition of Surface Soil

Desirable soil composition consisting of 50% pore space, 25% air, 25% water, 40% solid material.

Particle Density (PD)

Density of soil particles, typically 2.65 gm/cu cm for average soils.

Bulk Density (BD)

Ranges from 1.0 to 1.8 gm/cu cm and depends on the amount of pore space in soil.

Soil Structure

The way soil particles clump together into aggregates or peds, classified by type, class, and grade.

Soil Consistence

The behavior of soil under pressure at different moisture levels: wet, moist, and dry.

Soil Tilth

Ease of tillage, seedbed preparation, and plant rooting movement.

Compaction

Pressure applied at the soil surface that reduces pore spaces.

Porosity

The space within soil that can hold water

calculated by the ratio of water volume to total volume or from bulk density and particle density

Which has greater porosity, sand or clay?

Clay at 50%, sand is lower at about 30%

Permeability

The ease with which air, water, and roots move through soil, influenced by pore characteristics.

Adhesion

The property of water that allows it to stick to solid surfaces.

Cohesion

The property of water that allows it to stick to other water molecules.

Capillary Action

How water moves through narrow spaces based on the interactions with surrounding surfaces.

Micropores

Small pores that retain water even after saturation and drainage.

Macropores

Large pores that allow rapid movement of water and air, facilitating drainage.

Saturated Soil

Soil condition where pores are fully filled with water.

Gravitational Water

Water that drains from macropores under the influence of gravity.

Field Capacity

Moisture level in soil after drainage, when water remains in micropores.

Mostly accessible by plants

Capillary Water

Water held in micropores due to capillary action, accessible to plants.

Permanent Wilting Point

Soil moisture level at which plants can no longer extract water.

Available Water

Water available for plants, existing between field capacity and permanent wilting point.

Water Holding Capacity

The amount of water soil can retain for plant use.

Functions of soil in ecosystem

o   Support growth of plants (medium for root growth and supplies nutrients)

o   Control fate of water in hydrological system

o   Function as natures recycling system

o   Provide habitat for living organisms (small mammals to microscopic organisms0

o   Engineering medium in human built environments

Things that plants obtain from soil

o   Physical support

o   Air

o   Water

o   Temperature moderation

o   Protection from toxins

o   Nutrient elements

Macronutrients

Plants use in large amounts, to include:

Nitrogen

Phosphorous

  Potassium

  Calcium

Magnesium

  Sulfur

  Carbon

  Hydrogen

  Oxygen

Micronutrients

Plants use in relatively small amounts, to include:

Iron

  Manganese

  Boron

  Zinc

  Copper

  Chlorine

  Cobalt

  Molybdenum

  Nickel

Soil Profile

Vertical section of soil exposing various horizons.

Parent Material

The starting material from which soil develops, can be consolidated or unconsolidated.

Regolith

A layer of unconsolidated rock and mineral debris.

Saprolite

Weathered rock that has become loose enough to be dug with a spade.

Pedology

The study of soils and their relationships to landscapes.

Soil Horizons

Layers of soil that form different characteristics from surface to depth.

Soil Ventilation

o   Allows carbon dioxide to escape

o   Allows oxygen to enter

Humus

o   Organic waste that converts the mineral nutrients in the waste into forms that can be utilized by plants and animals

O Horizon

Organic horizon rich in unprocessed organic material like leaves and sticks.

- Raw material that soil organisms will process (consume/alter) in some way

-  Becomes humus when waste material from soil organisms process and yield a useable product or nutrients available for pants/soil organisms

A Horizon (Topsoil)

Surface layer enriched with dark organic matter, essential for nutrient creation.

-  Organic material is largely processed and available for use

-  Nutrient creation layer – soil roots and organisms are continually creating new forms of soil nutrients

-  Creates and reshapes organic materials (leaches into lower layers)

-  Lower layers contain less organic material and referred to as subsoil

E Horizon

Layer of nutrient leaching, sometimes leaving a coarse sandy structure.

-Does not always occur

- Leaching leaves a coarse and sandy layer (finer silts and clays drained to lower layers)

-  B horizon is biggest recipient of leached nutrients from E horizon

B Horizon

Mineral layer receiving leached nutrients from above, less organic material.

- Most organic material has leached down from above

-  Some physical/chemical weathering processes occur, but mainly recipient of nutrients/organic matter from above

-  Can be an abundance of unprocessed minerals from weathered parent material

C Horizon

Least weathered, lowest soil horizon with little to no nutrients.

-  Little to no nutrients (light in color)

-  Roots and soil organisms less common (Can still affect physical/mechanical/chemical processes)

-  Processes typically less frequent than upper layers

Soil Solution

Water that contains dissolved organic and inorganic substances.

Neutral Solution

Solution with equal concentrations of H+ and OH- ions.

Acidic Solution

Solution where H+ ions outnumber OH- ions.

Alkaline Solution

Solution where OH- ions outnumber H+ ions.

Root Interception

Roots continuously growing into new, undepleted soil zones.

Mass Flow

Nutrients dissolved in water moving toward roots absorbing soil moisture.

Diffusion

Process whereby nutrient ions move from areas of higher to lower concentration around root surface

Soil Quality

Measure of a soil's ability to perform ecological functions.

Common processes that lead to degradation of soil quality

o   Erosion that removes topsoil

o   Accumulation of salts in improperly irrigated soil in arid regions

o   Soil is cultivated and crops are harvested without returning organic material and mineral components