NRES 201 Lectures 8-9 (Fall 2014): Soil Classification11NRES 201Soil Classification2Today’s lecture topics- Rationale for classification- Soil taxonomySoil ClassificationNRES 201 Lectures 8-9 (Fall 2014): Soil Classification23Rationale for classificationSoil heterogeneity- The five soil-forming factors interact to produce nearly endless variety in soils- More than 23,000 soil series mapped in the USA- And many more thousands worldwide- Soil formation never stops- So the variety expands over time4Soils as individuals- Soils vary, but they alsomerge into one mass- Soils characterized as pedons- The smallest 3-dimensionalunit that has all the prop-erties of a particular soil- Occupies 10-100 ft2of land- A polypedon is a group ofsimilar pedons- And constitutes a soilindividual- A soil series consists of allsoil individuals whoseproperties fall within a certain rangeSource: http://www.studyblue.comNRES 201 Lectures 8-9 (Fall 2014): Soil Classification35Reasons for soil classification- To organize knowledge of soils- To better understand relationships among soils- To provide information pertinent to similar soilselsewhere in the world 6Soil taxonomyBases of classification- The surface part of the pedon (epipedon)- Organic matter, texture, color, structure,cation composition- The subsurface part of the pedon- Drainage, color, accumulation of clay/Fe/Al/Ca/Na- Climate- Moisture and temperature regimesNRES 201 Lectures 8-9 (Fall 2014): Soil Classification47Diagnostic surface horizons- Mollic epipedon- Formed under grass- Dark-colored- Thick- High organic matter (1-30%)- High in basic cations(Ca2+, Mg2+, K+)Source: http://nspss.unl.edumollic epipedon8- Umbric epipedon- Like a mollic epipedon,but more acidic• Low in Ca2+, Mg2+, K+- Forms in areas with higherrainfallSource: http://courses.soil.ncsu.eduumbric epipedonNRES 201 Lectures 8-9 (Fall 2014): Soil Classification59- Ochric epipedon- Mineral horizon that does notqualify as a mollic or umbricepipedon• Too thin• Too light in color• Too low in organic matterSource: http://courses.soil.ncsu.eduochric epipedon10- Melanic epipedon- Developed from volcanic ash- Thick, black mineral horizonwith a high organic mattercontent (> 10%)- Light in weight and fluffySource: http://www.agronomy.lsu.edumelanic epipedonNRES 201 Lectures 8-9 (Fall 2014): Soil Classification611- Histic epipedon- Formed in wet areas- Thick organic horizon overlying a mineral soil- Light in weight and fluffySource: http://soils.cals.uidaho.eduhistic epipedon12- Summary- Total of eight epipedons- We’ve covered the five most importantSource: Brady and Weil (2008)NRES 201 Lectures 8-9 (Fall 2014): Soil Classification713Diagnostic subsurface horizons- Albic horizon- Light-colored eluvial (E)horizon depleted of clayand Fe and Al oxides- Low in fertilitySource: http://en.wikipedia.orgalbic horizon14- Argillic horizon- Illuvial (Bt) horizon with clayaccumulation- 3-20% higher clay contentthe overlying A or E horizon- Clay accumulates:• On ped surfaces• Between sand grains• As pore liningsSource: http://www.cals.uidaho.eduargillic horizonNRES 201 Lectures 8-9 (Fall 2014): Soil Classification815- Natric horizon- Illuvial (Btn) horizon withaccumulation of clay and Na- Columnar or prismaticstructure- High pH- Poor physical properties dueto soil dispersion- Occurs in arid and semiaridregionsSource: http://www.studyblue.comnatric horizon16- Cambic horizon- Illuvial (Bw or Bg) horizonlimited in clay accumulation- May show carbonatedepletionSource: http://www.cals.uidaho.educambic horizonNRES 201 Lectures 8-9 (Fall 2014): Soil Classification917- Kandic horizon- Illuvial horizon withaccumulation of low-activityclay and Fe and Al oxides- Occurs below an abruptboundary- Common in the southeasternUSASource: http://courses.soil.ncsu.edukandic horizon18- Oxic horizon- Illuvial horizon with extensiveaccumulation of low-activityclay and Fe and Al oxides- High in clay but not sticky- Found in humid tropical andsubtropical regionsSource: http://www.cals.uidaho.eduoxic horizonNRES 201 Lectures 8-9 (Fall 2014): Soil Classification1019- Spodic horizon- Illuvial horizon with accumulation of organicmatter and Fe/Al oxides- Often coarse-textured- Found in highly leached forest soils of cool, humidclimatesspodic horizonSource: http://www.friendsofsylvania.org20- Calcic horizon- Illuvial (Bk) horizon with accumulation of CaCO3- Found in arid and semiarid regionsSource: http://courses.soil.ncsu.educalcic horizonNRES 201 Lectures 8-9 (Fall 2014): Soil Classification1121- Summary- Total of 19 diagnostic subsurface horizons- We’ve covered eight of the most important- Of these eight, only the albic horizon is eluvial- The others are illuvial:• Argillic• Natric• Cambic• Kandic• Oxic• Spodic• Calcic22Moisture regimes- Aquic- Soil saturated with water- B horizon gleyed and mottled- Udic- Soil moisture seldom limits plant growth- Common in humid regions- Ustic- Soil moisture more limiting for plant growth- Drought periods occur- Aridic- Soil dry for at least half of the growing season- Typical for arid regions- Xeric- Mediterranean-type climate- Drought periods in the summerNRES 201 Lectures 8-9 (Fall 2014): Soil Classification1223Temperature regimesIllinois fits here24Categories and nomenclature- Six hierarchical categories- The upper five followsystematic nomenclature- Series named after a town,river, or other geographicfeature near where theywere first recognizedSource: Brady and Weil (2008)NRES 201 Lectures 8-9 (Fall 2014): Soil Classification1325Today’s lecture topics- Rationale for classification- Soil taxonomySoil Classification26Today’s key concepts- Soils are classified according to the properties of their surface and subsurface horizons.- These properties have a critical impact on soil use and management.NRES 201 Lectures 8-9 (Fall 2014): Soil Classification1427Today’s lecture topics- The benefit of taxonomy- Soil orders- Lower-level taxonomic categoriesSoil Classification28- Soils are inherentlyheterogeneous- But they can be groupedaccording to commonproperties- Huge potential forsimplification- From 23,000 series- To 12 ordersSource: Brady and Weil (2008)The benefit of taxonomyNRES 201 Lectures 8-9 (Fall 2014): Soil Classification1529Entisols (...ents)- Dominant soil forming factor:time- Few if any profile features- No diagnostic B horizon- The most common soil orderglobally- Diverse group that includes:- Floodplain