Lecture 7: Introduction to Soil Formation and Classification

Lecture 7: Introduction to Soil Formation and Classification

Soil Texture and Color Analysis Lab Results

Soil A: Topsoil from Prof. Catalano s backyard Soil B: Soil above beach at Castlewood State Park 10YR 3/2: 8 10YR 4/3: 6 10YR 4/2: 3 10YR 3/4: 2 10YR 3/3: 1 10YR 3/3: 8 10YR 3/2: 7 10YR 4/2: 2 10YR 2/3: 1

Soil C: Subsoil from Prof. Catalano s backyard Soil D: Surface soil on Missouri River floodplain: River Valley Dr @ MO-364 10YR 4/3: 6 10YR 3/3: 6 10YR 4/2: 5 10YR 3/4: 1 10YR 3/2: 1 10YR 4/4: 1 7.5YR 3/1: 7 2.5Y 3/2: 6 2.5YR 3/2: 2 2.5Y 3/1: 2 10YR 2/1: 1 10YR 2/2: 1

Soil E: Surface soil from center of Castlewood State park Soil F: Topsoil, Mississippi R. floodplain, N of confluence with Missouri R. 10YR 3/3: 11 7.5YR 3/2: 4 10YR 3/2: 4 5YR 3/1: 1 2.5Y 2.5/1: 4 10YR 2/1:1 2.5Y 3/1: 4 7.5YR 2.5/1: 3 2.5Y 3/1: 2 2.5Y 2/1: 1 10YR 3/1:1

Soil J: Topsoil, Mississippi R. floodplain, S of confluence with Missouri R. Soil K: Topsoil, Mississippi R. floodplain, S of confluence with Missouri R. 2.5Y 2.5/1: 4 7.5YR 3/1: 1 2.5Y 3/2: 3 5Y 2.5/1: 3 10YR 2/1: 3 2.5Y 3/1: 2 2.5YR 3/1: 2 7.5YR 2.5/1: 5 5Y 2.5/2: 5 2.5Y 2.5/1: 2 2.5Y 3/1: 2 2.5YR 2.5/1: 2 5Y 3/1: 1

Introduction to Soil Formation We will go into more detail April 4 & 6!

One Planet, Different Soils Andisol Spodosol Aridisol Mollisol Alfisol Ultisol

Major Soil Forming Processes Additions: Organic matter from dead plants added to soil surface Wind-blown dust Transformations: Mineral weathering Degradation of organic matter Translocations: Organic matter moving into A horizon Clays moving from A to B horizon Losses: Erosion and leaching by water Decomposition of organic matter to CO 2 Two example processes are listed for each categories, this list is not exhaustive!!!

Factors Controlling Soil Formation 1. Parent material: Soil precursor 2. Climate: Temperature and precipitation 3. Biota: Native vegetation, microbes, soil animals, humans 4. Topography: Slope, aspect, landscape position 5. Time: Duration of exposure of parent material to soil forming processes

Parent Material Review: Rocks and Major classes of rocks: Sediments Igneous: Formed from cooling of molten rock Sedimentary: Formed from lithification of sediments upon burial at Earth s surface Metamorphic: Formed from alteration of igneous or sedimentary rocks Key types of sediment materials: Sand & Silt: Typically composed of quartz [SiO 2 ] Clay: Dominated by microscopic aluminosilicate minerals Loess: Wind-blown silt produced by glaciers; rock flour

Weathering: Turning Parent Material into Soil

Primary and Secondary Minerals

Climate Climate determines the nature and intensity of weathering of parent material Temperature and precipitation are the major climate variables that affect soil formation

Global Atmospheric Circulation Dry Wet Dry Wet Dry Wet Dry

Variation in Soil Depth with Latitude From: Schaetzl and Anderson (2005) Soils: Genesis and Geomorphology

Influences of Biota

Topography

(Granite in SE United States) Time

Interaction of Soil Forming Factors

Key Concepts in Introductory Soil Formation Four Major Soil Forming Processes: Additions, Transformations, Translocations, Losses Five Major Soil Forming Factors: Parent Material, Climate, Biota, Topography, Time The combined effects of Soil Forming Factors determines the Soil Forming Processes that occur, and have occurred in the past, in a specific location, controlling the soil in that environment

Introduction to Soil Classification We will go into more detail March 30 and April 2!

Concept of Individual Soils Soil varies across a landscape, but soils in specific locations display specific characteristics The smallest unit to display a set of unique characteristics is called a pedon A group of similar, closely associated pedons is called a polypedon or soil individual

Soil Taxonomy A comprehensive classification system for soils Hierarchical structure System is based on soil properties that can be observed and measured Diagnostic soil horizons Clay type and content Base saturation Provides a universal means of discussing soils Well-documented, publicly available method for fully naming any soil on Earth

Official Soil Classification System Available at: https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/survey/class/

Official Instruction Manual Available at: https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/survey/class/

Categories in Soil Taxonomy

12 Soil Orders Alfisols Andisols Aridisols Entisols Gelisols Histosols Inceptisols Mollisols Oxisols Spodosols Ultisols Vertisols

Argillic Horizon Alfisols Moderately leached soils with a clay-rich B-horizon Typically found in forests Andisols Short-range-order (SRO) minerals are common Form in volcanic ash Aridisols Dry and often saline soils Form in arid regions

Histic Epipedon Entisols Little or no evidence of soil formation Often sandy or shallow Gelisols Contain permafrost Found in arctic and high alpine regions Histosols Dominantly organic soil material, no permafrost Wetlands, bogs, marshes

Mollic Epipedon Oxic Horizon Inceptisols Soils with altered horizons but no accumulations Young soils, still developing Mollisols Dark surface layer rich in base cations Found in grasslands Oxisols Highly leached soils with iron and aluminum oxides Found in tropical regions

Albic Horizon Spodic Horizon Argillic Horizon Argillic Horizon Spodosols Accumulation of Fe/Al and OM below leached horizon Found in coniferous forests Ultisols Highly leached soils with a clay-rich B-horizon Found in warm, humid forested regions Vertisols High content of swelling clay; deep cracks when dry Shrink-swell behavior

I AM A SUAVE HOG Inceptisols Alfisols Mollisols Andisols Spodosols Ultisols Aridisols Vertisols Entisols Histosols Oxisols Gelisols I GAVE US OMAHA Inceptisols Gelisols Alfisols Vertisols Entisols Ultisols Spodosols Oxisols Mollisols Andisols Histosols Aridisols