Understanding the U.S. Soil Taxonomy: Categories, Properties, and Regimes, Slides of Biology

Download Understanding the U.S. Soil Taxonomy: Categories, Properties, and Regimes and more Slides Biology in PDF only on Docsity! Unit 4: Soil Taxonomy Docsity.com Objectives • Understand categories of the U.S. taxonomic system • How soil properties help distinguish soil families • Knowledge of locations of various soil orders • Investigate how soil temps and moistures are categorized Docsity.com U. S. System of Soil Taxonomy • Gellisols – Must have permafrost in the top 6’ • Mollisols – Most extensive soils in the U.S. – Naturally fertile, slightly leached – Can be semiarid to subhumid climates • Alfisols – Fertile in favorable moisture conditions – Usually very productive • Ultisols – Leached, acidic – Moderate to low fertility Docsity.com U. S. System of Soil Taxonomy • Aridisols – Arid-region soils – Can be very productive • Oxisols – Hot, wet tropics – Conducive to year-round plant growth • Spodosols – Found mostly in cool climates – Poorest soils for cultivation – Must have lime & fertilization to grow crops Docsity.com U. S. System of Soil Taxonomy – Suborder • Differentiated based on soil properties & horizons • Soil moisture, soil temp, dominating effects of chemical or textural features – Great Groups • Differentiated by soil horizons & soil features – Accumulated clay, iron, humus, hard pans/cement layers – Subgroup • Three kinds of subgroups – Represent the central (typic) concept of the soil group – Properties that intergrade towards other groups, etc. Docsity.com Soil Moisture & Temperature Regimes • Soil Moisture Regimes – Attempt to indicate the extent of naturally available water in the soil depth of maximum root proliferation – Aquic • Wet w/ anaerobic saturation long enough to produce visual evidence of poor aeration – Peraquic • Tidal marsh or inland depression where groundwater is always at or near the surface Docsity.com Soil Moisture & Temperature Regimes – Udic • Usually has adequate water throughout the yr – Perudic • Extremely wet, percolation in all months when not frozen – Ustic • Moisture is limited but is present during the growing season – Xeric • Deficient in water & w/ a dry cropping season • Most precipitation in the winter Docsity.com Soil Moisture & Temperature Regimes – Aridic • Very water deficient • Long dry periods, short wet periods • Soil Temperature Regimes – Based on the mean annual soil temp (MAST) – Mean summer soil temp – Mean winter soil temp – Determined at ~2’ depth – Cryic • MAST 46° F Docsity.com Additional Terminology for Family Groupings • Particle-size Classes – Fragmental • Mostly stones, cobbles, gravel, etc. • Fine-earth component <10% of soil volume – Sandy skeletal • >35% rock fragments • Fine-earth fraction is sand, sandy loam – Loamy skeletal • >35% rock fragments • Fine-earth fraction loamy Docsity.com Additional Terminology for Family Groupings – Clayey skeletal • >35% rock fragments • Fine-earth fraction >35% clay – Sandy • Texture is sand, loamy sand – Loamy • Finer than sand or loamy, <35% clay – Clayey • >35% clay – Very fine • >60% clay Docsity.com Additional Terminology for Family Groupings • Soil Mineralogy Classes – Ferritic: >40% iron oxide in fine-earth fraction – Kaolinitic: >50% kaolinite & other 1:1 or nonexpanding clay – Carbonatic: >40% carbonates plus gypsum – Magnesic: >40% magnesium-silicate minerals – Smectitic: clayey soil w/ more smectite than any other clay – Siliceous: >90% silica minerals – Mixed: not dominated by any mineral type Docsity.com Docsity.com Histisols • Organic soils formed in cold or wet regions • Can occur almost anywhere • Found in FL, LA, GA, some in the Great Lakes states • Large area found in Canada Docsity.com Ee 9 ° > — iQ © ° a  Docsity.com DOMINANT SUBORDERS (ES Aquents (I Orthents WM Arents (2) Psamments Aiea Fluvents Docsity.com Inceptisols • Weakly developed soils • More development than Entisols • Mostly found in Middle Atlantic & Pacific states, northern Rockies • Develop in many climates • Largest area globally found in China Docsity.com Docsity.com DOMINANT SUBORDERS GS Aquands (MM Udands (1) xerands (EE cryands (BD ustands (MS torrands (MMM Vitrands Doesity.com Aridisols • Long dry periods, short periods of wetness • Found in the U.S. primarily in the western mountain states & Pacific states • Low rainfall, scattered grasses, desert shrubs • Rank second worldwide in area to Entisols Docsity.com Mollisols • Dark-colored soils of grasslands & some hardwood forests • Deep, dark-colored, fertile A horizon (mollic epipedon) – Mollic epipedon extends from surface to ~2’ depth • Properties & Classification of Mollisols – Large number of suborders – Naturally fertile – Easily managed Docsity.com Mollisols • Management of Mollisols – Formed under grasses, forests – Tend to be most fertile soil – High humus content – High concentration of N – In wetter climates don’t need irrigation, but in dryer areas can produce highly – May become acidic – Black soil colors to depth of 2-3’ Docsity.com Mollisols – 1/5 of the U.S. soils – Can withstand much variation in cropping – Limited leaching – Quite fertile, even w/out fertilization – Little to no lime needed – Only Alfisols may have high natural productivity – Texture, depth, climate make it ideal for cropping and highly valuable Docsity.com DOMINANT SUBORDERS MM Albolils MBB) Rendolls ME) Xerolls BY Aquolls HBB Udolls z= Cryolls BS Ustalls Docsity.com Vertisols • Self-mixing soils, >30% shrink/swell clays • Found mostly in central & southeastern TX & along lower Mississippi River Docsity.com Ee = Vera Alfisols • Management of Alfisols – If topography & climate are favorable; alfisols can be very productive – Most are leached of lime, and can have an acidic zone • If leached enough, forms an E horizon – Erosion exposing clays at the surface not favorable for plant growth – Most naturally productive soils w/out fertilization or irrigation Docsity.com Alfisols – Usually will require lime amendments – Alfisols & Mollisols generally located in a region’s breadbasket • Distribution of Alfisols – North-central states & mountain states – Occur on all continents – Corn belt of IN, OH, MI, WI, IL – Woodland soils in TX, CO Docsity.com Docsity.com ot i lil ae = eat aii Doesity.com _  Docsity.com Ultisols • Warm, humid regions • Usually too acidic to be classified as a Mollisol/Alfisol, not weathered enough to be an Oxisol • Located in southern Atlantic states, eastern south-central states, Pacific sates Docsity.com Oxisols • Most extensively weathered soils • Typically found on old landforms in tropical, subtropical climates • Found only in HA, Puerto Rico, Guam • Extensive in South America, Africa Docsity.com Do€sity com  PUERTO RICO DOMINANT SUBORDERS ey Aquox = Udox [0 Perox HR Ustox i Torrox — US. 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