Soil analysis

Soil forensic analysis

The use of soil and geosciences to aid in criminal investigations; soils can act like fingerprints and be used as markers to tie a victim or suspect to a particular location.

Soil

An interdisciplinary science; defined as 'alive' ('Soils are alive, dirt is dead'). Its four components are Air, Water, Mineral matter, and Organic matter.

Dirt

Defined as 'dead'.

Mineral matter

A component of soil. Larger particles are rock, while smaller particles are single minerals. Soil particles range over four orders of magnitude.

Organic matter

A component of soil; traps water and is a major source of nitrogen and phosphorus via decomposition. Although only a small proportion of mass, its importance should not be downplayed.

Humus

Gives organic matter a black/brown color; it is a collection of organic compounds called humic acids that are resistant to decay.

Soil texture

Determined by the relative abundance of the three mineral particles (sand, silt, and clay).

Soil structure

How the soil is aggregated.

Sand

The largest mineral particle size: 2.0 - 0.05 mm or 0.05 - 2 mm. It is composed of a single mineral (SiO2).

Silt

Medium mineral particle size: 0.05 - 0.002 mm or 0.002 - 0.05 mm. It feels smooth or silky, is composed of weatherable minerals, and has low plasticity when wet.

Clay

The smallest mineral particle size: < 0.002 mm. It has a large surface area to absorb water, high plasticity when wet, and fine clays behave as colloids.

Munsell color system

The standard system used to determine soil color, based on three characteristics: Hue, Value, and Chroma.

Hue

A characteristic used in the Munsell color system; refers to the redness or yellowness of the soil.

Value

A characteristic used in the Munsell color system; refers to the lightness or darkness (where 0 = black).

Chroma

A characteristic used in the Munsell color system; refers to the brightness (where 0 = grey).

Soil taxonomy

The hierarchical grouping of soils. The broadest level of organization consists of 12 orders.

Pedon

A fundamental unit of soil classification.

Soil series

A class of soils (20,000 in the U.S.). Units on soil maps are named based on this class. They are named after the town they were first identified.

Diagnostic horizons (Epipedons)

Features characterizing soil orders. Their presence or absence determines the order.

Soils moisture regime

A feature characterizing soil orders; refers to the presence or absence of water saturated conditions.

Nomenclature (Orders)

Soil orders are named for characteristics and genesis features, and their names end in 'sols'.

Entisols

(Ent - recent): Weakly developed mineral soils that have no B horizon. Lacking soil formation due to short exposure time, dry climate, steep slopes, or cultivation.

Inceptisols

(Ept - inception): Exhibit the beginning of a B horizon—more profile development than Entisols. Not found in arid climates.

Andisols

(And - Japanese, ando means 'black soil'): Formed from volcanic ash or other ejecta. Characterized by Andic properties (low density, high-water holding capacity, P fixing). Usually fertile and high in organic matter.

Gelisols

(El - Greek, gelid means 'very cold'): Defined by permafrost within 100 cm. Contains Cytoturbation (frost churning) within 100 cm.

Histosols

(Ist - Greek, histos means 'tissue'): Composed of organic soil (20-30% OM) and is more than 40 cm thick. Little development, usually due to prolonged saturation.

Aridisols

(Id - Latin, aridus means 'dry'): CaCO3 containing, dry soils of arid regions. They support plant growth for less than 90 days.

Vertisols

(Ert - Latin, verto means 'turn'): Dark, swelling, and cracking clays (30% or more clays at 50 cm). Known for Slickensides (cracking during dry season).

Mollisols

(Ol - Latin, mollis means 'soft'): Defined by a Mollic epipedon (dark in color from OM). Has high base saturation (>50%) and is typical of the Great Plains.

Alfisols

(Alf - Nonsense symbol): Highly weathered (less than Spodosols or Ultisols). Develop under native deciduous forests and have high-to-medium base saturation.

Ultisols

(Utl - Latin, ultimus means 'last'): Defined by an Agrillic or kandic horizon (yellow and reddish colors from Fe oxides). They are strongly leached, acidic forest soils with low base saturation and native fertility.

Spodosols

(Od - Greek, spodos means 'wood ash'): Characterized by a light-colored E horizon overlaying a reddish-brown spodic zone (Fe and Al oxides complexed with humus). Found in cold, temperature regions.

Oxisols

(Ox - French, oxide for 'oxide'): Defined by Oxic, never argillic horizons. They are the most highly weathered of all soils, generally nutrient poor, and found in inter-tropical regions.

Cytoturbation

Also known as 'Frost churning'; a characteristic found within 100 cm of Gelisols.

Slickensides

A characteristic of Vertisols; refers to the cracking that occurs during the dry season.

Mollic epipedon

A diagnostic horizon that is dark in color due to organic matter, defining Mollisols.

Spodic zone

The reddish-brown zone in Spodosols where Fe and Al oxides are complexed with humus.

Oxic horizon

A horizon defining Oxisols; Oxisols never have argillic horizons.