Soils Classified (USDA System)

1. Terminology a. class: A group of individuals that are similar in

selected properties. b. category: A group of classes. c. hierarchical system: A system having a number of

categories differing in level of generalization, such that each class within a category is also a subclass of a class within any higher category.

2. Categories of the USDA System Order (12 total), ex. Spodosol Suborder, ex., Aquod Great Group, ex., Alaquod Subgroup, ex., Aeric Alaquod Family, ex., sandy, siliceous, hyperthermic, Aeric Alaquod Series, ex., Myakka

Syllables used to designate classes

Formative elements for Orders are as follows:

Alfisols - alf Inceptisols - ept Andisols – and Mollisols - oll Aridisols – id Oxisols - ox Entisols – ent Spodosols - od Gelisol – el Ultisols - ult Histosols – ist Vertisols - ert

Useful formative elements at suborder level are:

Aqu - Frequently saturated to surface or near surface. Fluv - Evidence of stratification from flooding. Fibr - High amount of undecomposed organic matter. Hem - High amount of organic matter, moderately decomposed. Sapr - High amount of highly-decomposed organic matter. Ud - Humid climate, but soil not too wet. Ust - Intermediate rainfall, soil not too wet. Xer - Dry climate, soil not too wet. Torr - Hot, dry climate; soil not too wet. Orth - Nothing extreme or distinctive. Umbr - Umbric (dark, thick, low-base surface horizon).

3. Diagnostic Horizons

a. Examples of Diagnostic Surface Horizons (Epipedons)

Histic: high organic C content (generally > 12%) Mollic: soft, dark, thick, high base saturation Umbric: soft, dark, thick, low base saturation Ochric: Essentially a default

b. Examples of Diagnostic Subsurface Horizons (Epipedons)

Albic: light-colored due to loss (eluviation) of components Argillic: zone of clay accumulation via translocation Spodic: zone of preciitation of organo-metal components

chemically translocated from another zone Salic: zone of soluble salt accumulation Sulfuric: low pH, yellow mottles from Fe sulfate minerals

4. Soil Orders that occur in Florida Histosols - Dominated by organic soil material Spodosols - Have Spodic. May have Argillic Mollisol - Have Mollic & BS ≥ 50%. May have Argillic Alfisols - Have argillic and BS ≥ 35% in lower part Ultisol - Have argillic and BS < 35% in lower part Inceptisol - Have Umbric or Histic (in some cases Mollic) Entisol - Default. Absence of most diagnostic horizons to 2 m

Examples of Entisol Great Groups

• Suborder Aquents (Wet Entisols)

• Great Groups Cryaquents - cold Fluvaquents - floodplain Hydraquents - water Psammaquents - sand Epiaquents - perched

5. Categories & Nomenclature Examples Credit Wade Hurt for this a subsequent slides

Examples of Entisol Great Groups

• Suborder Fluvents (Floodplain

soils)

• Great Groups Torrifluvents - torrid (hot and dry) Tropofluvents - tropical (warm and humid) Udifluvents - humid (not dry in most years) Ustifluvents - semi-arid (between Udic-Aridic) Xerofluvents - semi-arid (Mediterranean climate)

Examples of Entisol Great Groups

• Suborder Psamments (Sandy Soils)

• Great Groups Cryopsamments Quartzipsamments -

Quartz Torripsamments Udipsamments Ustipsamments Xeropsamments

Examples of Subgroups

4 3 2 1 Typic Fluvaquents

4 1 2 Typical Entisols with aquic moisture regimes 3 that occur on floodplains. 1. Order 3. Great Group 2. Suborder 4. Subgroup (typical concept of Fluvaquents

Examples of Subgroups

4 3 2 1 Mollic Fluvaquents

1 2 Entisols with aquic moisture regimes that 3 occur on floodplains & have thick, 4 dark surface layers. 1. Order 3. Great Group 2. Suborder 4. Subgroup (intergrading toward a Mollisol)

Examples of Subgroups

4 3 2 1 Aeric Fluvaquents

1 3 2 Entisols on floodplains with aquic moisture regimes that are not so wet. They are better 4 aerated in the “upper” part of the soil profile. 1. Order 3. Great Group 2. Suborder 4. Subgroup (intergrading toward a more aerated subgroup)

“Sidebar”:Aquic Soil Moisture Regimes

• Typic subgroup of an aquic suborder: • Typic ____aqu____

– wettest • Aeric subgroup of an

aquic suborder: • Aeric ____aqu____

– better aerated • Aquic subgroup:

• Aquic ___________ – driest

From Mausbach 1992

Nature of Number Differentiating Category of Taxa Characteristics

The Family name consists of a series of descriptive terms that modify the subgroup name. Note: Family name adds no knowledge to understanding of wet soils.

Family Many

Nature of Number Differentiating Category of Taxa Characteristics

May have virtually the full range of properties permitted in a family, but range is restricted in one or more properties. Note: since the series name adds no knowledge to our understanding of wet soils it the series level of soil classification will not be discussed.

Series 17,000+

Typic Haplosaprists

7. Practice

Typic Haplosaprists • What does the taxonomic classification

mean? • Is it likely, not likely, or maybe hydric?

– Histosol dominated by sapric material (wet). – Likely to be hydric. Large areas of this soil converted

to crop land in south Florida.

Aquic Paleudalfs

Aquic Paleudalfs • What does the taxonomic classification

mean? • Is it likely, not likely, or maybe hydric?

– Alfisol with aquic conditions moderately deep in profile. – Likely to be nonhydric. Has water table in E horizon for

brief periods during high rainfall. In an aquic subgroup.

Aquic Quartzipsamments

Aquic Quartzipsamments

• What does the taxonomic classification mean?

• Is it likely, not likely, or maybe hydric? – Entisol that is sandy, dominated by quartz sand, with

aquic conditions moderately deep in profile. – Likely to be a nonhydric soil. In an aquic subgroup.

Seasonal high water table at about 24 inches.

Typic Argiaquolls

Typic Argiaquolls • What does the taxonomic classification

mean? • Is it likely, not likely, or maybe hydric?

– Mollisol with aquic conditions near surface and accumulation of clay in subsoil.

– Likely to be hydric. Hydric soils commonly classify in an aquic suborder; “argi” is “double whammy” (will explain).

Aeric Alaquods

Aeric Alaquods • What does the taxonomic classification

mean? • Is it likely, not likely, or maybe hydric?

– Spodosol with aquic conditions near surface; not quite as wet as “typic” subgroups.

– Maybe hydric. Typical Spodosol on flatwoods. In an aquic suborder.

Class as Likely Hydric, Maybe Hydric, or Likely Non-Hydric

• Typic Haplosaprists Terric Haplosaprists

• Lithic Cryofolists Aquic Paleudalfs

• Aquic Glossudalfs Typic Aquisalids

• Aquic Quartzipsamments Typic Humaquepts

• Typic Argiaquolls Argiaquic Argialbolls

• Aeric Calciaquolls Aeric Alaquods

• Typic Umbraquults Chromic Epiaquerts

Answers According to Hurt

• Likely Hydric – Typic Haplosaprists Terric Haplosaprists – Typic Humaquepts Typic Umbraquults – Typic Argiaquolls Typic Aquisalids – Chromic Epiaquerts Argiaquic Argialbolls

• Maybe Hydric – Aeric Calciaquolls Aeric Alaquods

• Likely Nonhydric – Aquic Glossudalfs Aquic Paleudalfs – Aquic Quartzipsamments Lithic Cryofolists

Summary

• Likely Hydric: Soils in the Albolls Suborder or soils with a formative element at the Suborder level of soil classification (Aqu, Fibr, Hist, and Sapr.), unless they have the formative element aeri at the suborder level & soils in the following Great Groups Aquisalids, Historthels, and Histoturbels.

• Maybe Hydric: Soils with a formative element at the Suborder level of soil classification (Aqu, Fibr, Hist, and Sapr.) and the formative element aeri at the suborder level & soils on flood plains such as Aquic Dystrochrepts, Aquic Eutrochrepts, & Aquic Udifluvents.

• Likely Nonhydric: Soils with all other classifications including aqu at the Subgroup level of soil classification with some exceptions (note the three example given above).