GEOG 1113: Landform Geography Soils July 2, 2013

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

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

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

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