Spodosols

Spodosols

Soils with spodic horizon (organic with or w/out Fe)

>10 cm thick, within 200 cm of surface

Commonly coarse-textured

Albic horizon above is common, NOT required

Bhs—often cemented in parts (orstein-like), difficult to dig (Fe-cemented)

Two temperature regimes– cryic/frigid

thermic

State Factor ConsiderationsParent material and vegetation are the overriding factors Acid, sandy parent material Coniferous vegetation to produce acid leachate high in fulvic acids

Time is also a factor since development of a well-expressed spodic horizon requires a minimum of 3 to 5,000 years Weakly expressed spodic horizons may form in a few hundred years.

Spodosols are found on a variety of landscapes and reliefsClimate must be such that conifers can grow, but there are no other restrictions

DistributionOccur in humid tropical, sub-tropical, cool temperate and boreal areas with coarse-textured parent materialsOccupy about 4.2% of the earth's land surface

Distribution

Problems and Use

Acidity is the major problem

Most Spodosols are either in cold climates or need drainage for agricultural production

Used for forest, blueberries (acid tolerant crop), and citrus (in Florida if soil is drained).

Spodosols have been used for other agricultural crops with addition of lime and fertilizers

AridisolsCentral concept: soils with pedogenic development in arid regions. They either have an aridic moisture regime, or they are saline.

Aridisols must have a diagnostic subsurface horizon If no diagnostic horizon is present, the soil is an EntisolSoils that do not supply water to plants for long periodsCalcic, petrocalcic, and salic horizons are common Lack of leaching from low rainfall results in subsoil accumulation of

the more soluble salts

State factor considerations: Climate is the overriding factor Time is important since the soil must have a diagnostic horizon Can have any parent material, relief, and vegetation (xerophyllic)

Aridisols

Problems and use: Most obvious limitation is lack of water Accumulation of salts more soluble than gypsum is also

serious problem in some areas Soluble salts are toxic to certain plants and can limit availability of

water for plants (high osmotic potential) Salt accumulations can cause structural damage to buildings and

corrosion of steel and concrete.

The major use for Aridisols is for rangeland grazing Motorcycles and dune buggies are also a major use in

some areas

Distribution

Distribution

Aridisols

Aridisols

AndisolsSoils developed from volcanic ejecta and composed of andic soil materials

Only order criterion is 36 cm of andic soil materials in the upper 60 cm of the soilAny vegetation, landscape position, or climate

Andic Soil MaterialsSoil material with properties characteristic of volcanic ash, cinders, and other pyroclastic materials Volcanic materials have an abundance of amorphous silicate components such as allophane and imogolite Low bulk density High P fixation High amounts of Fe and Al extracted with acid oxalate Oxalate extraction will dissolve amorphous Fe, Si, and Al

components but not crystalline components

Andic criteria are designed to separate soils with a high content of amorphous components from soils with crystalline components

AndisolsDominant pedogenic processes are weathering and mineral transformation Translocation is minimal.

State factor considerations The only important factor is parent material. Time is a minor factor

A few 10's or 100's of years to weather fresh ash to produce oxalate soluble components

Biology, climate, and relief are not important Transitional soils With enough weathering, amorphous components will

transform to crystalline minerals and properties associated with andic soil materials will be lost

Andisols

Andisols are generally highly productive soilsFavorable physical and chemical propertiesP fixation may highFew engineering problems.

Andisol Distribution124 million hectares worldwide Pacific Rim of Fire Rift Valley of Africa, the west coast of Italy, the West Indies, and Iceland

Andisols

Andisols

VertisolsSoils with combination of amount and type of clay to have a high shrink-swell potentialOccur in an environment with wet and dry periods to induce shrink-swellThree requirements must be met for a soil to classify as a Vertisol:1. 25 cm thick layer in the upper 100 cm of soil that has either

slickensides close enough to intersect or wedge shaped peds with their long axis tilted 10 to 60o from horizontal; and

2. 30% or more clay in all horizons between the soil surface and a depth of 50 cm or to a lithic or paralithic contact or petrocalcic horizon, if shallower than 50 cm; and

3. cracks that open and close periodically.

VertisolsThe most common feature of Vertisols is occurrence in an environment with seasonal drying of the soil profileAlso common among Vertisols are parent materials with a basic reaction, i.e. basic igneous rocks, chalks, marls, basalt, etc. Vertisols also often occur in basins Accumulation of basic cations and Si from mineral weathering in

upslope positions Maintainence of high Si in soil solution is important for smectite

stability

Vegetation is commonly grassland or savannah - rarely forest.Vertisols are often referred to as self-mulching Strong structure at surface behaves more like sand than clay

VertisolsGenesis of Vertisols requires substantial volume changes2 models for slickenside formation Self-swallowing

SwellingSwellingSwelling

Soil Mechanics

σ0 = σV = σL

σ0

σ0 = cohesion + internal friction

σV

σL σL

σV Dry Soil

σ0

σ0 = σV > σL

σL > σ0 > σV

Moist and Shallow

σ0 σLσL

σV

Moist and Deep

σ0

σ0 < σL ≤ σV = shear failure

σV

σL σL =

Vertisol Features

Vertisol Features

Gilgai

State Factor ConsiderationsParent material and climate are the overriding factors. The parent material must have either minerals that weather to clays that induce shrink-swell or this type of clay

Climate must result in Either continually moist or dry and no volume change

Relief is sometimes a factor Basins and other low position where cations and Si

accumulateVegetation and time are not important

Shrink SwellClays with high shrink-swell are not necessarily smectitic Volume change is not from changes in interlayer spacing Volume change is due to change in thickness of the water shell surrounding

clay particles and packets Clay particle size is more important than type

Kaolinite – 1-2 µm Smectite <0.2 µm

Flexibility of the clay also has an influence Fine-grained kaolinite (volcanic derived) may have high shrink-swell

Distribution

Distribution

Problems and UseVertisols are one of the most difficult classes of soils to manageShrink-swell creates many engineering problems Foundation stability Roads Lime stabilization

Ca vs. Na saturated clays

Agronomic problems include water erosion water excess and deficiency low trafficability when wet high P fixation high energy demand for tillage

Histosols

Histosols are soils composed of organic soil materials

10

12

14

16

18

20

22

0 20 40 60 80

Clay, %

Org

an

ic C

, %

To be a Histosol, more than half of the upper 80 cm of the soil must be organic soil materials (>40 cm)

Organic Soil Material

Mineral Soil Material

FiberFragment or piece of plant tissue, excluding roots, that is retained on a 100-mesh sieve (0.15 mm) after dispersion separate with sodium hexametaphosphate.Fiber content of organic material determined in the field is rubbed fiber Material is rubbed 10 times between the thumb and

forefinger Fiber content is estimated

Decomposition state has a large impact on many soil properties including water holding capacity, bulk density, hydraulic conductivity, etc.

Fiber Content Affect on Soil Properties

Type of Organic Material

Bulk Density Water

Content at Saturation

Fiber Content

Mg m-3 g g-1

Fibric <0.1 8.5-30 >2/3 Hemic 0.1-0.2 4.5-8.5 1/3-2/3 Sapric >0.2 <4.5 <1/3

Control SectionSurface to either 130 or 160 cm thick depending on kind of organic material Unconsolidated mineral substratum does not limit the

depth of the control section Lithic or paralithic contact, water, or frozen soil is lower

limit

Control section divided into 3 tiers: Surface tier - upper 30 cm (60 cm if the organic material

is fibric) Subsurface tier - next 60 cm from base of surface tier Bottom tier - next 40 cm from base of subsurface tier

Properties that Affect Classification

Hydric - soils that have a layer of water within the control sectionLimnic - limnic materials >5 cm thick within control sectionLithic - organic materials rest on lithic contact within the control sectionTerric - a mineral layer other than limnic materials is 30 cm or more thick and its upper boundary is within the control section

Suborders

Saprists - sapric material dominant

Hemists - hemic material dominant and/or have sulfuric horizon within 50 cm of the soil surface or sulfidic materials within 1 m or the surface

Fibrists - fibric material dominant

Folists - not saturated with water for more than a few days and is composed of leaf litter, twigs, and branches resting on rock or fragmental materials

Family CriteriaParticle-size class - refers to mineral layer of terric subgroups Mineralogy class - Ferrihumic - Fe oxides mixed with organic materials Terric subgroups - mineral mineralogy classes applied to mineral part of soil Limnic subgroups - limnic layers within the control section 5 cm or more thick

Coprogenous Diatomaceous Marly

Reaction classes Euic - pH is 4.5 or more in 0.01 M calcium chloride in at least some part of

the subsurface tier Dysic - pH less than 4.5 throughout subsurface tier

Soil temperature classes - same as mineral soilsSoil depth classes - same as mineral soils

State Factor ImpactsTime - needed to accumulate and decompose organic matterParent Material Rock type is not important Type of organic material can affect accumulation and decomposition rates

Relief Important in warm climates

Flat landscapes and depressions with saturated conditions Less important for Folists and Fibrists in cold climates

Blanket bogs

Climate - affects organic matter decomposition Cold Wet

Organics - various types of plants will contribute to Histosol formation Sphagnum mosses are common precursor to Fibrists

DistributionBoreal climatesWarm wet climates with low relief landscapes South Florida Southeast Asia

Distribution

Use ConsiderationsDrainage Saturation is a limitation for most soil uses Saturated conditions cause Histosol formation Drainage leads to Histosol destruction

Subsidence through organic matter decomposition is a major problem Subsidence rates up to 3 cm per year in Florida

Use ConsiderationsIn areas of crop production, the water level is controlled to prevent the soil's destruction Water table is maintained at the

surface during most of the year Soil only drained when necessary

for a production operations

In addition to subsidence, organic materials are not rigid. and as water in pores is removed, the material collapses

Use ConsiderationsHistosols are used in many areas for vegetable or citrus production Fertile with high CEC, adequate moisture, good tilth, etc. Mostly high-value crops because of cost of drainage and to control

the water table

Histosols have been historically and are still being used for fuelDemand for use as potting soil, wrapping material, etc.Histosols have severe limitations for use in roads, buildings, etc. High water tables Low bearing capacity and strength Subsidence.

SeriesLowest category in Soil Taxonomy More than 19,000 series in the United States

Purpose is mainly pragmatic Closely related to interpretations

Differentiae used for series are the same as those used for classes in other categories Series properties cannot range across limits of classes in

higher categories Cecil must be a fine, kaolinitic, thermic Typic Kanhapludult Rion must be a fine-loamy, siliceous, themic Typic Kanhapludult Cataula must be a fine, kaolinitic, themic Oxyaquic Kanhapludult

Many families only have one series

Greater Restriction within a Family

Fine, kaolinitic, thermic Typic Kanhapludults Cecil – Bt horizon has hue of 2.5YR or redder Appling – Bt horizon has hue of 5YR or yellower

fine-loamy, siliceous, thermic Plinthic Kandiudults Tifton – common Fe stone in upper Bt Dothan – no Fe stone in upper Bt

Distinctions within a family are restrictions in the range of one or more properties of the family Only those differences that serve to distinguish one series

from another are included in statements of series differences

3 Tests of Series Differentiae

Properties serving as differentiae can be observed or can be inferred with reasonable assuranceDifferentiae must create soil series having a unique range of properties Difference among series should be greater than normal errors made

by qualified pedologists

Differentiae must reflect a property of the soils Can be reflected in the nature or degree of expression of one or

more horizons. Can be almost any horizon or soil property

May also be Landscape property Commonly associated soils Climate

We may not be as smart as we think

Phase

Properties that may influence certain but not all uses of a soil Slope Stoniness Aspect “Wind swept”

Not a part of Soil Taxonomy

Utilitarian classification that can be superimposed at any categorical level to permit more precise interpretations for soil use

Competing Series Statement - CecilThese are the Appling, Bethlehem, Madison, Nankin, Pacolet, Tumbleton,

and Wedowee series in the same familyThose in closely related families are the Aragon, Braddock, Cataula,

Chestatee, Cullen, Georgeville, Hayesville, Herndon, Hulett, Kolomoki, Lloyd, Mayodan, Mecklenburg, Spotsylvania, Tatum and Wedowee series

Appling soils have dominant hue of 7.5YR or yellower or where hue is 5YR it has evident patterns of mottling in a subhorizon of the Bt or BC horizon

Aragon soils contain fragments of chert, and have a cherty limestone C horizon.

Bethlehem soils are moderately deep to weathered bedrock of sillimanite schist, phyllite schist, or mica schist.

Braddock and Hayesville soils are mesicCataula soils have a fragipan, Chestatee soils contain more than 15

percent, by volume, of coarse fragments throughout the pedon . . . . . . .

Piedmont Series Key

Upper 50 cm of Bt horizon has >35% clayBt horizon has hue of 5YR or redder

Upper part of Bt horizon has common mica flakes - Madison

Bottom of Bt horizon with more than 35% clay is 45 to 75 cm below the surface – Pacolet

Bottom of Bt horizon with more than 35% clay is more than 75 cm below the surface – Cecil