Soil Classification & Taxonomy PDF

Soil Classification SOIL TAXONOMY  Soil Taxonomy This formal term refers to the system of classification developed by the USDA Soil Survey.  Individual Soils Pedon – A hexagonal column of soil measuring from 1 to 10m2 in top surface area. A pedon is the basic samp...

Soil Classification SOIL TAXONOMY  Soil Taxonomy This formal term refers to the system of classification developed by the USDA Soil Survey.  Individual Soils Pedon – A hexagonal column of soil measuring from 1 to 10m2 in top surface area. A pedon is the basic sampling unit used in soil surveys. Polypedon – An essential soil individual, comprising an identifiable series of soils in an area. It is made up of multiple pedons and has distinctive characteristics that differentiate it from surrounding polypedons. Series - A soil series is a class of soils and the basic units used to classify soils. Nearly 400 soil series in the Phil. Soil Individual  The principles of Soil Taxonomy are: Classify soils on basis of properties Soil properties should be readily observable and / or measurable Soil properties should either affect soil genesis or result from soil genesis  Soil Taxonomy - Purpose 1. Organize knowledge about soils 2. Understand relationships among different soils 3. Establish groups or classes for practical purposes. a. predicting behavior b. identifying best uses c. estimating productivity d. extending research results  Requirements Temperature Regimes – mean annual soil temperature measured at 50 cm from surface Moisture Regimes – number of days when soil contains available water during the period when soil temperature at 50 cm below the surface is above 5oC Diagnostic Horizons – distinct types of horizons that reflect nature of soil formation Epipedon – surface diagnostic horizons Subsurface diagnostic horizons Mineralogy – dominant type of clay minerals Particle size distribution – proportion of coarse fragments (2 mm – 74 mm size particles) in combination with fine fragments ( - % organic matter Ochric - thin, light colored - surface layers that do not fit any of the above  Comparison of Epipedons Ochric Histic lighter more thinner color organic matter Mollic low base saturation Umbric  Diagnostic Subsurface Horizons Argillic - illuvial horizon of clay accumulation - Bt Natric - same as argillic but with > 15% exchangeable sodium (Na) - Btn  Diagnostic Subsurface Horizons Spodic - illuvial accumulation of oxides of Al and Fe (sesquioxides) and OM, red or dark red color - only found in acid sandy soils, with high rainfall- generally found below E horizon. Contains a Bhs or Bs horizon  Oxic - very weathered layer of only Fe and Al oxides and 1:1 clay minerals, low pH and not very fertile (found in tropical soils) Bo Cambic - slightly altered layer - not weathered enough to be argillic, Bw horizon designation or development of color and or structure NONE - no diagnostic subsurface horizon present  Comparison of Subsurface Diagnosic Horizons Spodic Cambic less more Al developed and Fe Argillic very more sodium weathered Oxic Natric  Soil Taxonomy Soils are divided into six distinct categories based on diagnostic characteristics  Soil Taxonomy Fine-loamy mixed, mesic Aquic Argiudolls 1) Orders – presence or absence of diagnostic horizons 2) Suborders – subdivide soil order based on moisture and temperature regime 3) Great Groups – subdivide suborder based on differences between soil horizons 4) Subgroups – typic (central concept of the great group); intergrades or transitional forms to other orders, suborders, or great groups; extragrades or additional properties not common to great group characteristics 5) Family – particle size, mineralogy, temperature regime, etc. 6) Series – parent material; kind, number and arrangement of horizons in the profile  Family Fine-loamy, mixed, superactive, mesic Aquic Argiudolls Sub Sub Group Order Family Texture, clay minerals, CEC, temp, Great Order Group Based on soil properties that affect management and root penetration, such as texture, temperature, and depth  Lipa Series = Fluvaquentic Epiaquoll Fine-loamy mixed, isohyperthermic Fluvaquentic Epiaquoll Sub Sub Order Family Group Great Order Named from the town or Group landscape feature near where the soil was first recognized (Lipa)  12 Soil Orders Each Order has a diagnostic epipedon and subsurface horizons – which could be “none”.  12 Soil Orders Entisol Ultisols Inceptisol Oxisols Andisols Aridisols Spodosols Vertisols Mollisols Histosols Alfisols Gelisols  Entisol - ent Recent soils - minimal development, little horizonation, young soils. Entisol A R  Entisols: Entisols: Characteristically have A/C or A/R profiles, exhibit only ephemeral soil development - largely confined to surface horizon. May have an Ap horizon.  Vertisol - ert Inverted - soils with high clay content, large shrink swell potential - gradually invert on themselves, Vertisol = Bss at slickenslide soil cracks Slickenslide Global Distribution of Vertisols  Inceptisol - ept Inception - soil shows the beginning of horizon development, little or no illuviation,  Aridisols - id Arid regions of the world (19%), < 10 in A of rainfall, usually contain Bw carbonates, Bk C Aridisol A Bt Bk Bkqm R  Aridisol NaCl Salt accumulates on Az the surface and Bz in the C1 subsurface. C2  Mollisols - oll soils with thick, dark, soft surface - mollic + cambic, natric, argillic or none - high base saturation - soils of the grassland Global Distribution of Mollisols  Spodosols- od acid sandy soils with thick E and red Bhs - ochric and spodic  Alfisol -- alf fertile forested soils with ochric and argillic - high base saturation (> 35%) -forested soils Global Distribution of Alfisols  Ultisols - ult soils more weathered than Alfisols - A ochric E and argillic - low Bt1 base saturation < 35% - Bt2 redder and more acid than Alfisols BC Global Distribution of Ultisols  Histosols - ist peat soils - organic material - histic Peat – undecomposed to slightly decomposed o.m. in waterlogged areas Muck – highly decomposed o.m.  Andisols - and soils from volcanic volcanic ejecta (ash, cinder, pumice, basalt) : very light, A low bulk density early-stage secondary Bw minerals (allophane, imogolite, ferrihydrite 2BC clays), High P fixing capacity 2C  Oxisols - ox Soils with Oxic horizon - very weathered - soils of the tropics. low pH - acid soils - high in 1:1 clay minerals Global Distribution of Oxisols  Gelisol - el New Order as of 1998 - soils with permafrost (formerly Cryochrepts - or frozen Inceptisols)  Gelisols Soils formed in cool climate (pergelic temperature regime) · Any parent material · Often: Glacial drift