This module is designed to offer a firm set of facts that every student involved in agronomic, or environmental sciences should know, by heart.
The information offered below is presented in a condensed manor suitable for flash card study and examinations can be drawn from every bit of this.
The bold words are terms to commit to memory.
source of a) support, b) nutrients, c) water, and d) air
organic wastes are broken down and nutrients are released
a handful of soil contains billions of organisms from thousands of species
water storage and cleansing
building material and support for building
Approximately 50% solids and 50% pore space
decomposed rocks (45-50% -percent by volume)
remains of plants and animals (0-5%)
The study of structure or form; properties characterized by sight, feel, smell or sound
distribution of particle sizes (sand, silt, and clay)
how particles are arranged
grade, size and type
the ability of particles to stick together (adhesion and cohesion forces)
size and abundance
size and abundance
Example = Bt2 horizon
Master Horizon - Major soil horizons identified by capitol letters (O, A, E, & B: included capitol letter non-soil layers C, R, M, & W)
Layer - A term borrowed, likely from geologists, to indicate parallel sheets of a quantity, or thickness of material, typically one of several, covering a surface or body that are laid down by natural forces. Short version of layer - parallel sheets of material laid down by natural forces.
Note: R is sometimes called a horizon, but this is incorrect as R is a layer. A horizon is actually a special kind of layer. To be a horizon the layer is distinguished from a layer as having been formed or differentiated by "soil forming processes."
O horizon or layer
a surface layer dominated by organic materials (> 20% organic carbon)
The i, e, & a are subordinate designators and modify the O
- a mineral horizon, <20% organic carbon, which forms at the surface or beneath an O horizon
- characterized by a darker color than the rest of the profile due to the accumulation of organic matter; high biological activity
- eluvial horizon (loss of materials such as iron/aluminum oxides and clays)
- an intensively leached eluvial horizon in which organic matter along with iron/aluminum oxides and clay have been removed; most commonly found in forest soils
- typically white or light gray in color due to the lack of coatings on the mineral surfaces
horizon formed beneath an A, E or O horizon and is a zone of accumulation (illuvial horizons). May accumulate clay, iron/aluminum oxides, organic matter, carbonates, etc.
C horizon or layer
a layer of unconsolidated material showing little weathering (alteration) and biological activity (e.g., beach sand, alluvium deposited by rivers, glacial till deposited by glaciers)
consolidated rock that can not be dug with a shovel and shows little evidence of weathering (e.g., granite, sandstone)
layer can include organic and limnic (limnic = of or pertaining to fresh water; freshwater) materials. deposited in water by precipitation or through the actions of aquatic organisms, such as algae and diatoms, or derived from underwater and floating aquatic plants and subsequently modified by aquatic animals. They are used only in Histosols (organic soil)
root limiting subsoil layer consisting of nearly continuous, horizontally oriented, human-manufactured materials
indicates water layer(s) within or beneath the soil. [Wf if frozen; so the f is for frozen]
A special kind of horizon that contain properties of two types of master horizons.
Example = AB horizon - has a dark color due to organic matter (A-like), plus red color due to accumulation of iron (B-like)
Common transition horizons: AB, BA, BC, CB
The dominant master horizon designation is listed first.
Note: Topsoil is a term that is depreciated in soil science
Topsoil purchased at a materials yard may not be soil at all!