© 2007, John Wiley and Sons, Inc. Physical Geography by Alan Arbogast Chapter 11 The Global Distribution and Character of Soils Lawrence McGlinn Department of Geography State University of New York - New Paltz

© 2007, John Wiley and Sons, Inc. Global Distribution & Character of Soils What is soil? Measurable soil characteristics Soil chemistry Soil profiles (reading the soil) Soil science & classification

© 2007, John Wiley and Sons, Inc. What is Soil? Uppermost layer of Earth’s surface with mineral & organic matter able to support plants Transition between atmosphere & rocky Earth Provides plants with physical support, nutrients & water Plants support soils by anchoring them to Earth

© 2007, John Wiley and Sons, Inc. Basic Soil Properties Inorganic Material – minerals - natural elements or compounds w/crystalline structure – silicon, aluminum, iron, potassium, calcium, etc. common in soil minerals Organic Matter – bacteria & fungi break down remains of plants & animals to form humus – helps soil hold water and increases fertility

© 2007, John Wiley and Sons, Inc. Basic Soil Properties Water – from rain & snow Losses to evapotranspiration Drainage through soil, leaving air pockets Capillary Action – attraction to soil particles Surface tension holds some water in soil Field capacity – max. water capacity of soil Soil-Water Budget – balance of soil-water gains & losses

© 2007, John Wiley and Sons, Inc. Soil-Water Budget

© 2007, John Wiley and Sons, Inc. Basic Soil Properties Air – most air in soil is carbon dioxide Plants give off CO 2 during respiration & take it in during photosynthesis Less air in wet soil because of water

© 2007, John Wiley and Sons, Inc. Soil-Forming Processes Soils form & evolve through sequence of interrelated pedogenic (soil-forming) processes: Soil Additions Translocations Soil Depletions Transformations

© 2007, John Wiley and Sons, Inc. Soil-Forming Processes Transformation Eluviation Illuviation

© 2007, John Wiley and Sons, Inc. Soil-Forming Factors Factors that consistently affect how soils form Parent Material Climate Organisms Relief Time

© 2007, John Wiley and Sons, Inc. Parent Material Sediment in which soil forms – related to geology of the region Residual Parent Material – sediment from rock that weathers in place Regolith – small fragments of weathered rock Transported Parent Material – carried by wind, water, or glaciers from where it weathered

© 2007, John Wiley and Sons, Inc. Regolith & Soil

© 2007, John Wiley and Sons, Inc. Climate Temp & moisture influence the kind & rate of biological and chemical reactions in soil More reactions in warm, wet conditions, so thicker, more developed soils Wetter soils have more eluviation & deeper illuviation b/c of water percolating downward African Climate, Vegetation & Soils

© 2007, John Wiley and Sons, Inc.Organisms Plants & animals that reside in soil They acquire food from soil & regulate its environment Bioturbation – mixing of soil by plant roots and burrowing animals Earthworms important as soil recyclers Micro-organisms decompose organic matter to humus

© 2007, John Wiley and Sons, Inc. Relief Differences between highs and lows of landscape – Mts are high relief, plains low relief Soils thin & poorly developed on steep slopes Sediment eroded more on steep slopes Sediment deposited more on areas of low relief where soils deeper & more developed

© 2007, John Wiley and Sons, Inc. Elluviation and Illuviation

© 2007, John Wiley and Sons, Inc.Bioturbation Prairie Dog Ant Hills, Australia

© 2007, John Wiley and Sons, Inc. Relief and Soil

© 2007, John Wiley and Sons, Inc. Conservation

Time Longer time on a stable surface allows for greater soil development Soil in a 10,000-yr-old floodplain more developed than soil on 2000-yr-old sand dune

© 2007, John Wiley and Sons, Inc. Measurable Soil Characteristics Physical Properties to Distinguish Soil Types: Color Texture Structure Soil Chemistry Soil pH

© 2007, John Wiley and Sons, Inc. Color Can indicate composition of soil, e.g. Humus-rich soil usually dark/black Iron-rich soil usually reddish color Munsell Color Chart based on 3 factors: Hue - composition of light reflection Value – lightness/darkness of soil Chroma – strength of color

© 2007, John Wiley and Sons, Inc.Texture 3 Size Categories for Soil Particles: Sand (largest), silt, & clay (smallest) Textural class based on combined % of these categories Texture important to water flow through soils & nutrient holding capacity Loamy soil, not too much clay or sand, best for agriculture

© 2007, John Wiley and Sons, Inc. Textural Triangle Clay – Horizontal Lines Sand – Bottom to upper left Silt – Upper right to bottom

© 2007, John Wiley and Sons, Inc. Soil Texture

© 2007, John Wiley and Sons, Inc.Structure How soil particles naturally clump together in peds, natural soil aggregates Key to how water and roots penetrate soil

© 2007, John Wiley and Sons, Inc. Soil Profiles Soil processes lead to vertical organization in soil, layers in a profile visible in cross-section Soil Horizon – distinct layer in soil profile Horizons blend into each other, no sharp boundaries Soil profiles vary in different regions of Earth, depending on soil-forming factors

© 2007, John Wiley and Sons, Inc. Fully Developed Soil Profile Base of Soil Soil Horizon Development

© 2007, John Wiley and Sons, Inc. Evolution of Midwest US Soil Soil Horizon Development

© 2007, John Wiley and Sons, Inc. Soil Science and Classification Goal of soil science to understand Earth’s soils in order to preserve & efficiently utilize them Classification in US based on soil taxonomy: color, texture, structure & mineral content Soil Order – highest level in soil taxonomy 12 soil orders occur on Earth Soil orders subdivided into many categories

© 2007, John Wiley and Sons, Inc. Twelve Soil Orders

© 2007, John Wiley and Sons, Inc.Ultisols Warm, moist, sub-tropical – 9% of land – some laterization, but more fertile, less leaching than oxisols – may include clay - support forest E – Eluviation t – texturally distinct, Silicate clay

© 2007, John Wiley and Sons, Inc.Spodosols Cool, humid regions, poleward of alfisols – 3% of land – podzolization – acidic – infertile – support mixed conif/decid forest h – humic acids s - sesquioxides

© 2007, John Wiley and Sons, Inc.Entisols Young soils – 16% of land – poorly developed - no E or B horizons – A horiz. – climate dry or parent material is quartz sand or recent transport

© 2007, John Wiley and Sons, Inc. Inceptisols Older than entisols – 10% of land - limited horizons, A & Bw – usually on transported parent material