GEOG 1113: Landform Geography Lecture 1: Soils Earth’s Internal Structure

Global Distribution & Character of Soils What is soil? Basic soil characteristics Soil-forming processes and factors Soil profiles (reading the soil) Soil science & classification Earth’s internal structure

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

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

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

Soil-Water Budget

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

Soil-Forming Processes Soils form & evolve through sequence of interrelated pedogenic (soil-forming) processes: –Soil Additions –Translocations –Soil Depletions –Transformations

Soil-Forming Processes

Soil-Forming Factors Factors that consistently affect how soils form –Parent Material –Climate –Organisms –Relief –Time

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

Regolith & Soil

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

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

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

Elluviation and Illuviation

Bioturbation Prairie Dog Ant Hills, Australia

Relief and Soil

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

Measurable Soil Characteristics Physical Properties to Distinguish Soil Types: –Color –Texture –Structure –Soil Chemistry –Soil pH

Soil Texture Triangle

Soil Texture

Types of Soil Structure

Soil Sampling and Mapping Units

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

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

Earth’s Inner Structure Major Layers (outside-in): Lithosphere Upper Mantle Lower Mantle Outer Core Inner Core

Earth’s Interior

Lithosphere

Types of Crust

Asthenosphere

Isostatic Adjustment Figure 11.4

Earth’s Magnetic Field