NRES 201 Lectures 8 9 Fall 2014 Soil Classification NRES 201 Soil Classification 1 Soil Classification Today s lecture topics Rationale for classification Soil taxonomy 2 1 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Rationale for classification Soil 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 time 3 Soils as individuals Soils vary but they also merge into one mass Soils characterized as pedons The smallest 3 dimensional unit that has all the properties of a particular soil Occupies 10 100 ft2 of land A polypedon is a group of similar pedons And constitutes a soil individual A soil series consists of all Source http www studyblue com soil individuals whose properties fall within a certain range 4 2 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Reasons for soil classification To organize knowledge of soils To better understand relationships among soils To provide information pertinent to similar soils elsewhere in the world 5 Soil taxonomy Bases 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 regimes 6 3 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Diagnostic surface horizons Mollic epipedon Formed under grass Dark colored Thick High organic matter 1 30 High in basic cations Ca2 Mg2 K mollic epipedon Source http nspss unl edu 7 Umbric epipedon Like a mollic epipedon but more acidic Low in Ca2 Mg2 K Forms in areas with higher rainfall umbric epipedon Source http courses soil ncsu edu 8 4 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Ochric epipedon Mineral horizon that does not qualify as a mollic or umbric epipedon Too thin Too light in color Too low in organic matter ochric epipedon Source http courses soil ncsu edu 9 Melanic epipedon Developed from volcanic ash Thick black mineral horizon with a high organic matter content 10 Light in weight and fluffy melanic epipedon Source http www agronomy lsu edu 10 5 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Histic epipedon Formed in wet areas Thick organic horizon overlying a mineral soil Light in weight and fluffy histic epipedon Source http soils cals uidaho edu 11 Summary Total of eight epipedons We ve covered the five most important Source Brady and Weil 2008 12 6 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Diagnostic subsurface horizons Albic horizon Light colored eluvial E horizon depleted of clay and Fe and Al oxides Low in fertility albic horizon Source http en wikipedia org 13 Argillic horizon Illuvial Bt horizon with clay accumulation 3 20 higher clay content the overlying A or E horizon Clay accumulates On ped surfaces Between sand grains As pore linings argillic horizon Source http www cals uidaho edu 14 7 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Natric horizon Illuvial Btn horizon with accumulation of clay and Na Columnar or prismatic structure High pH Poor physical properties due to soil dispersion Occurs in arid and semiarid regions natric horizon Source http www studyblue com 15 Cambic horizon Illuvial Bw or Bg horizon limited in clay accumulation May show carbonate depletion cambic horizon Source http www cals uidaho edu 16 8 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Kandic horizon Illuvial horizon with accumulation of low activity clay and Fe and Al oxides Occurs below an abrupt boundary Common in the southeastern USA kandic horizon Source http courses soil ncsu edu 17 Oxic horizon Illuvial horizon with extensive accumulation of low activity clay and Fe and Al oxides High in clay but not sticky Found in humid tropical and subtropical regions oxic horizon Source http www cals uidaho edu 18 9 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Spodic horizon Illuvial horizon with accumulation of organic matter and Fe Al oxides Often coarse textured Found in highly leached forest soils of cool humid climates spodic horizon Source http www friendsofsylvania org 19 Calcic horizon Illuvial Bk horizon with accumulation of CaCO3 Found in arid and semiarid regions calcic horizon Source http courses soil ncsu edu 20 10 NRES 201 Lectures 8 9 Fall 2014 Soil Classification 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 Calcic 21 Moisture 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 summer 22 11 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Temperature regimes Illinois fits here 23 Categories and nomenclature Six hierarchical categories The upper five follow systematic nomenclature Series named after a town river or other geographic feature near where they were first recognized Source Brady and Weil 2008 24 12 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Soil Classification Today s lecture topics Rationale for classification Soil taxonomy 25 Today 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 26 13 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Soil Classification Today s lecture topics The benefit of taxonomy Soil orders Lower level taxonomic categories 27 The benefit of taxonomy Soils are inherently heterogeneous But they can be grouped according to common properties Huge potential for simplification From 23 000 series To 12 orders Source Brady and Weil 2008 28 14 NRES 201 Lectures 8 9 Fall 2014 Soil Classification Soil orders Entisols ents Dominant soil forming factor time Few if any profile features No diagnostic B horizon The most common soil order globally Diverse group that includes Floodplain soils Sand dunes Steeply sloping soils Soils subject to human disturbance Land area coverage 16 global 12 USA 5 suborders Aquents wet Arents disturbed Fluvents alluvial Orthents typical Psamments sandy Source