Presentation on theme: "An Abbreviated Key to Soil Orders"— Presentation transcript:
1 An Abbreviated Key to Soil Orders SOILS WITH--1. A. permafrost at <1 m; ORB. gelic materials at <1m and permafrost at <2mGELISOLS2. organic materials that are—A. 2/3 of thickness over lithic/paralithic contact, with no mineral horizons >10 cm; ORB. saturated >30 days/year, AND are >60 cm thick if fibrous OR >40 cm thick if sapricHISTOSOLS3. a spodic horizon >10 cm thick (with certain depth requirements)SPODOSOLS
2 4. andic soil properties in 60% of the soil within 60 cm of the surface or a lithic/paralithic contactANDISOLS5. an oxic horizon within 150 cm of soil surface AND no kandic horizon; OR>40% clay in top 18 cm AND kandic horizon with low weatherable minerals within 1 m of surfaceOXISOLS6. a layer >25 cm thick within 1 m of surface with slickensides or wedge-shaped peds, AND>30% clay in all horizons to depth of 50 cm or a lithic/paralithic contact, ANDperiodic cracking at soil surfaceVERTISOLS
3 7. aridic moisture regime AND ochric epidpedon AND one of following within 1 m of surface: cambic, gypsic, calcic, petrocalcic, petrogypsic, natric, OR argillicARIDISOLS8. argillic or kandic horizon AND % BS (ECEC) <35% in all horizons 125 below the top of argillic/kandic or to depth 180 below soil surface or to lithic/paralithic contactULTISOLS9. mollic epipedon AND %BS (pH 7)>50% in ALL horizons to 180 cm depth or to lithic/paralithic contactMOLLISOLS10. argillic, kandic, or natric horizon, OR fragipan with clay films in some partALFISOLS
4 11. cambic, calcic, gypsic, petrocalcic, OR petrogypsic horizon within 1 m of surface OR oxic or spodic horizon within 2 m of surface, OR sulfuric horizonINCEPTISOLS12. All other soilsENTISOLS
5 Lower Levels in Soil Taxonomy ORDERSUBORDERGREAT GROUPSUBGROUPFAMILYSERIES
7 Nomenclature of Lower Levels Suborders: names of suborders have two syllablesFirst connotes something about the soilSecond is the formative element from the orderUdalf - an Alfisol with a udic moisture regimePsamment - (psamm: sandy) an Entisol with a sandy particle size throughoutAquult - an Ultisol with an aquic moisture regimeGreat Groups: name consists of the suborder and a prefix that suggests something of the diagnostic properties of the soilPaleudalf - (Pale: old); an old (deeply weathered) UdalfUdipsamment - sandy Entisol with a udic moisture regime.Plinthaquult - wet Ultisol with plinthite.
8 Subgroups: name consists of the great group modified by one or more adjectives "Typic" - central concept of the great groupOther types of subgroups are:Intergrades toward other great groupsSpodic Udipsamment is an intergrade to Spodosols,Extragrades - subgroups not intergrading toward any known kind of soilLithic Udipsamment is a intergrade to not soil (hard rock within 50 cm of the soil surface)
9 Suborder Criteria Vary WIDELY with particular order --Meant to delineate MAJOR GROUPINGS within each orderHISTOSOLS:not saturated: FOLISTSsaturated:high fiber content: FIBRISTSlow fiber content: SAPRISTSintermediate fiber: HEMISTSFor MANY orders, suborder criteria are based on soil moisture regimes as way to separate broad classes within the order
10 Soil Moisture RegimesDetermine the potential use of the soil if use depends on water in the soilSuggest processes that have occurred or that are ongoing in the soilThe moisture regime, except for the aquic moisture regime, is the result of climate but is based on soil properties: soil moisture content.Dry soil - water content less than that held against 1500 kPa tensionMoist soil - water content is greater than that held against 1500 kPa tension but less than saturation.
11 Soil Moisture Regimes: Control Section Upper boundary - depth to which a dry soil will be moistened by 2.5 cm of water within 24 hours.Lower boundary - depth to which a dry soil will be moistened by 7.5 cm of water within 48 hours.These depths are approximately:10 to 30 cm for loams, silt loams, silts, clay loams, very fine sandy loams, silty clay loams, silty clays, sandy clay loams, sandy clays, and clays;20 to 60 cm for fine sandy loams and coarser sandy loams;30 to 90 cm for loamy sands and sands.
12 Moisture Regimes--Overview Aridic: MCS dry >180 d, moist for < 90 dno cropping possible; little soil developmentXeric: MCS dry >90 d, moist >180 d; winter rain/dry summerMediterranean; winter crops; some soil developmentUstic: MCS dry >90 d, moist >180 d; summer/uniform raincotton, irrigated crops; some soil developmentUdic: MCS dry for < 90 d; typically uniform raincorn cultivation; optimum soil developmentPerudic: udic, with monthly PPT>monthly ETcooler or very high rainfallAquic: redox features (<2 chroma) directly below A
18 Aquic Moisture RegimeSoils with an aquic moisture regime have aquic conditions immediately below an ochric epipedon or albic horizonAquic conditions:Horizons with aquic conditions are those that experience continuous or periodic saturation and reductionPresence of aquic conditions is indicated by redoximorphic features and is verified by measurement of saturation and reduction in the field.
19 Aquic Moisture Regime - Saturation Saturation - zero or positive pressure in the soil water. This can be determined be observing "free water" in an unlined auger hole.Duration of saturation is not specified.Three types of saturation are recognized:Endosaturation – saturated in all horizons from the upper boundary of saturation to 2 m or more.Episaturation – saturated in one or more horizons above horizons within 2 m that are not saturated (perched water table).Anthric saturation - variant of episaturation associated with controlled flooding for wetland rice.Produces reduction in the saturated surface soil and oxidation of reduced Fe and Mn in the oxidized subsoil.
20 Suborder Example: Ultisols Ultisols that have—1. Aquic conditions: redox features (including depletions) directly below the epipedon.AQUULTS2. >0.9% organic carbon in the upper 15 cm of the argillic/kandicHUMULTS3. A udic moisture regimeUDULTS4. A ustic moisture regimeUSTULT5. Other ultisols (presumably, xeric moisture regime)XERULTS
22 Great Group Example: Udults… Have a subsurface horizon with >50% (vol) plinthite: PlinthudultsHave a fragipan within 1 m of surface: FragiudultsHave a kandic horizon, and do not have a clay decrease of >20% (relative) within 150 cm of surface: KanidudultsHave a kandic horizon (with clay decrease) Kanhapludults(Have an argillic horizon and) do not have a clay decrease of >20% (relative) within 150 cm of surface: PaleudultsHave an epipedon with value of 3 or less throughout, AND in the upper 1 m of the argillic horizon, at least 50% of the volume has color hues of 2.5YR or redder and values of 3 or less: RhodudultsAll other Udults: Hapludults
23 Subgroup Examples (for Hapludults) Lithic contact at <50cm LithicSurface cracks and slickensides in subsurface Vertic<2 chroma depletions in upper 60 cm of argillic AquicFragic properties in 30% of subsurface layer >15 cm thick FragicSandy particle size in upper 75 cm of argillic PsammenticSandy particle size from surface to top of argillic atdepth of cm Arenicdepth of >100 cm Grossarenic….. (6 other ones: total of 14)OTHER Hapludults Typic
24 Family CriteriaSoil families serve purposes that are largely pragmatic and to enhance interpretation abilityFamily names include and are listed as part of the classification in the following order:Particle-size classMineralogy classCation-exchange activity class*Calcareous and reaction class *Soil temperature classSoil depth class *Soil rupture resistance or consistence class *Class of coatings (on sands) *Class of cracks *“Fine, kaolinitic, thermic” “Loamy-skeletal, mixed, mesic”
25 Key to Particle Size Control Section: A. For mineral soils that have a root-limiting layer within 36 cm of the mineral soil surface:From the mineral soil to the root-limiting layer; orB. For those Alfisols, Ultisols, and great groups of Aridisols and Mollisols that have an argillic, kandic, or natric horizon that has its upper boundary within 100 cm of the mineral soil surface and its lower boundary at a depth of 25 cm or more below the mineral soil surface or that are in a Grossarenic or Arenic subgroup:Either the entire argillic, kandic, or natric horizon if 50 cm or less thick, orthe upper 50 cm of the horizon if more than 50 cm thick; orC. For those Alfisols, Ultisols, and great groups of Aridisols and Mollisols have an argillic, kandic, or natric horizon that has its upper boundary at a depth of 100 cm or more from the mineral surface and that are not in a Grossarenic or Arenic subgroup:Between 25 cm from the mineral soil surface and 100 cm below the mineral soil surface or a root-limiting layer, whichever is shallower; orD. For other soils that have an argillic or natric horizon that has its lower boundary at a depth of less than 25 cm from the mineral soil surface:Between the upper boundary of the argillic or natric horizon and a depth of 100 cm below the mineral soil surface or a root-limiting layer, whichever is shallower; orE. All other mineral soils:Between 25 cm below the mineral soil surface and either 100 cm below the mineral soil surface or a root limiting layer, whichever is shallower.
27 PARTICLE SIZE FAMILIES For soils that are <50 cm to root-limiting layer, or are in a Lithic, Arenic, or Grossarenic subgroup: <35% clay in control section: “loamy” ≥35% clay in control section: “clayey” Soils that are >50 cm to a root-limiting layer use the following family names: 35-60% clay in control section: “fine” >60% clay in control section: “very fine” NOTE clay % for “textural classes” do NOT correspond exactly to this triangle…. Control sections that have >35% fragments use the following family names: --sand or loamy sand textures: “sandy-skeletal” --<35% clay: “loamy-skeletal” --≥35% clay: “clayey-skeletal” Family particle size name is NOT used with “psamments” (“sandy” family is implied) NOTE: “Lithic” families have lithic contact at <50 cm; “Arenic” families have cm of sandy particle size class at surface (A+E); “Grossarenic” have >100 cm sand at surface.
28 The weighted average is calculated by: Particle-Size ClassThe particle-size class is determined from the weighted average particle size within the control section.The weighted average is calculated by:SUM(% fraction horizon X thickness of horizon) / control section thickness
29 Particle-Size Control Section Weighted average clay = [(15 X 25) + (26 X 39) + (9 X 32)] / 50 = 33.5Weighted average sand = [(15 X 45) + (26 X 48) + (9 X 53)] / 50 = 48.0Family particle-size class is fine-loamy
30 Particle-Size Classes Three generalized particle-size classesclayey - >35% clayloamy - <35% claysandy – weighted average particle size is sand or loamy sandused for soils in shallow families and for soils in arenic, grossarenic, lithic, and pergelic subgroupsOther soils (fall-out key in Soil Taxonomy)Fragmental - <10% fine earth material (<2mm); >90% coarse fragmentsSandy-skeletal - sand or loamy sand texture and 35-90% coarse fragmentsLoamy-skeletal - <35% clay and 35-90% coarse fragmentsClayey-skeletal - >35% clay and 35-90% coarse fragments
31 Particle-Size Classes There are two situations in which particle-size class names are not used.The name is redundant, e.g. PsammentsThe soil is such that particle-size analysis is difficult to apply and particle-size does not adequately describe particle characteristicsSoils with andic propertiesFor anisols: terms used to replace particle-size classes include ashy, pumiceous, medial, hydrous, and others.Strongly contrasting particle-size classes:If the particle size changes significantly within the control section and the transition is less than 12.5 cm, terms are used to describe the strongly contrasting particle size classes, e.g. clayey over loamy.
32 Mineralogy ClassesControl section is the same as that for particle size.Mineralogy placement is dependent on particle-size class which determines the fraction of the soil used to determine mineralogyFor many soils, the mineralogy class is determined either for the whole soil (<2 mm) or for the sand and silt fractionsClay mineralogy specified only forOxisolsKandi and Kanhap great groupsSoils with fine, very-fine, clayey, or clayey-skeletal particle-size classMineralogy class is determined from the key for mineralogy classes
33 Common Mineralogy Classes for SE Soils Sandy or loamy particle-size classMineralogy of coarse silt and sand ( mm)Siliceous – >90% quartz and other resistant mineralsMixed – other soilsFine or very-fine particle size class and kandi or kanhap great groupsMineralogy of clay separate (<0.002 mm)Kaolinitic – >50% kaolinite and <10% smectiteSmectitic – more smectite than any other clay mineral
34 Cation-Exchange Activity Classes Intended to help interpret mineralogy and nutrient retention capacity of soils in mixed and siliceous mineralogy classesNot used in Histosols, Oxisols, kandi and kanhap great groups, or in soils with sandy or sandy-skeletal particle size classesControl section same as particle-size and mineralogyBased on CEC (pH 7.0) to clay ratiosuperactive - >0.60; smectite and other reactive claysactive to 0.60semiactive to 0.40subactive - <0.24; kaolinite and other low-activity clays
35 Calcareous and Reaction Classes Only used for selected taxaControl section - 25 to 50 cmClassesallic – high extractable Alcalcareous - effervesces with HCl in all of control sectionacid - pH <5.0 in 0.01 M CaCl2 (about 5.5 in water) throughout the control section.non-acid - pH >5.0 in 0.01 M CaCl2 in some or all of the control section - not used in family name of calcareous soils.
36 Soil Temperature Classes Mean annual soil temperature estimated by adding 1o C to mean annual air temperature.Classes of soil temperature:Pergelic - mean annual soil temperature <0o CPermafrost at a shallow depth.Cryic - mean annual soil temperature between 0 and 8o C and mean summer soil temperature is <15oFrigid - mean annual soil temperature between 0 and 8o C (mean summer temperature >15o C is implied)Mesic - mean annual soil temperature between 8 and 15o CCorn and winter wheatThermic - mean annual soil temperature between 15 and 22o CCotton and yellow pineHyperthermic - mean annual soil temperature is 22o C or higherCitrusFor frigid, mesic, thermic, and hyperthermic temperature regimes; an iso prefix is used if the mean summer and mean winter soil temperature differ by less than 6o C, i.e. isofrigid, isomesic, isothermic, and isohyperthermic.Designates tropical climates
37 Other Family Groupings Used to provide reasonable groupings of certain seriesMany of the characteristics are poorly understoodDepth of soil“shallow” - less than 50 cm (100 cm in Oxisols) to upper boundary of rock or root limiting horizon and not in lithic subgroupRupture Resistance“ortstein” and “noncemented” - used only for Spodosols.Classes of coatings - only used for Psamments“coated” - silt + (2 X clay) > 5“Uncoated” - silt + (2 X clay) < 5Classes of permanent cracks“Cracked” is the only classUsed only in Fluvaquents and Humaquepts
38 Series Lowest category in Soil Taxonomy Purpose is mainly pragmatic More than 19,000 series in the United StatesPurpose is mainly pragmaticClosely related to interpretationsDifferentiae used for series are the same as those used for classes in other categoriesSeries properties cannot range across limits of classes in higher categoriesCecil must be a fine, kaolinitic, thermic Typic KanhapludultRion must be a fine-loamy, siliceous, themic Typic KanhapludultCataula must be a fine, kaolinitic, themic Oxyaquic KanhapludultMany families only have one series
39 Greater Restriction within a Family Fine, kaolinitic, thermic Typic KanhapludultsCecil – Bt horizon has hue of 2.5YR or redderAppling – Bt horizon has hue of 5YR or yellowerfine-loamy, siliceous, thermic Plinthic KandiudultsTifton – common Fe stone in upper BtDothan – no Fe stone in upper BtDistinctions within a family are restrictions in the range of one or more properties of the familyOnly those differences that serve to distinguish one series from another are included in statements of series differences
40 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 propertiesDifference among series should be greater than normal errors made by qualified pedologistsDifferentiae must reflect a property of the soilsCan be reflected in the nature or degree of expression of one or more horizons.Can be almost any horizon or soil propertyMay also beLandscape propertyCommonly associated soilsClimateWe may not be as smart as we think
41 Phase Properties that may influence certain but not all uses of a soil SlopeStoninessAspect“Wind swept”Not a part of Soil TaxonomyUtilitarian classification that can be superimposed at any categorical level to permit more precise interpretations for soil use
42 Competing Series Statement - Cecil These 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 seriesAppling 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 horizonAragon 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
43 Piedmont Series Key Upper 50 cm of Bt horizon has >35% clay Bt horizon has hue of 5YR or redderUpper part of Bt horizon has common mica flakes - MadisonBottom of Bt horizon with more than 35% clay is 45 to 75 cm below the surface – PacoletBottom of Bt horizon with more than 35% clay is more than 75 cm below the surface – Cecil