Parent material materials underlying the soil and from which the soil
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Chapter 6 Land and Soil © 2009 Delmar, Cengage Learning Life Requirements • Life requires the presence of certain resources – water, sunlight, and soil • Soil is a valuable resource requiring careful management © 2009 Delmar, Cengage Learning Land, Soil, and Life • Soil makes up surface of Earth’s crust – unique blend of organic and inorganic material – allows for exchange of gases, water, minerals – necessary for life © 2009 Delmar, Cengage Learning Soil Formation • Forms extremely slowly – natural forces act on mineral and rock portions of Earth’s surface – atmosphere, sunlight, water, and living things • Soils vary in composition and character – temperature, organic matter, and amount of air and water © 2009 Delmar, Cengage Learning Soil Types • Types of soils differ with specific sites – shaped by forces of climate, living organisms, parent soil material, topography, and time © 2009 Delmar, Cengage Learning Origins of Soil • Parent material – materials underlying the soil and from which the soil was formed © 2009 Delmar, Cengage Learning Origins of Soil • General categories of soil parent materials – – – – – minerals and rocks glacial deposits loess deposits alluvial and marine deposits organic deposits © 2009 Delmar, Cengage Learning Minerals and Rocks • Minerals – solid, inorganic, chemically uniform, and naturally occurring substances © 2009 Delmar, Cengage Learning Minerals and Rocks • Rocks – aggregates of minerals – three major types • igneous: cooled molten material • sedimentary: solidification of sediment • metamorphic: other rock reformed by heat and pressure © 2009 Delmar, Cengage Learning Which is which? © 2009 Delmar, Cengage Learning Glacial Deposits • Massive rivers of slowly moving ice • Scrape across surface of Earth – scoop up surface material • When glaciers recede or melt, they leave material behind – great deposits of rocks, parent materials, and already formed soil materials © 2009 Delmar, Cengage Learning Loess Deposits • Collections of windblown silt • Create soil formations that look like drifting snow • Often create rich soil deposits – eastern Mississippi Valley – palouse soils of the Pacific Northwest © 2009 Delmar, Cengage Learning Alluvial and Marine Deposits • Soil deposits of waterborne sediments • Alluvial deposits – left by moving fresh water • moving water picks up sediment • as water slows, sediment deposited • creates alluvial fans © 2009 Delmar, Cengage Learning Alluvial and Marine Deposits • Marine deposits – Soil formed on ancient ocean floors • Soil in water drifts to bottom and collects © 2009 Delmar, Cengage Learning Organic Deposits • Lush plant life exists in swamps and marshes – Plants die and decay – Partially decayed material collects • forms muck or peat soils © 2009 Delmar, Cengage Learning Which is it? © 2009 Delmar, Cengage Learning Which is it? © 2009 Delmar, Cengage Learning Which is it? © 2009 Delmar, Cengage Learning Weathering • Minerals and rocks exposed to the weather break into smaller and smaller pieces © 2009 Delmar, Cengage Learning Weathering • Major weathering forces – – – – – temperature changes water action plant roots ice expansion mechanical grinding © 2009 Delmar, Cengage Learning Soil’s Organic Content • Decaying plant and animal parts – important part of formation and productivity of soil © 2009 Delmar, Cengage Learning Soil’s Organic Content • Organic matter may be in two basic forms – Original tissue • portion of organic matter that remains recognizable • twigs and leaves covering a forest floor – Humus • decomposed and constituents unrecognizable • gives topsoil its brown color © 2009 Delmar, Cengage Learning Soil’s Organic Content • Serves many important functions – – – – stabilizes soil structure as cementing agent returns plant nutrients to the soil helps store soil moisture makes soil more tillable for farming © 2009 Delmar, Cengage Learning Soil’s Organic Content – – – – provides food (energy) for soil microorganisms makes soil porous provides storehouse for nutrients minimizes leaching © 2009 Delmar, Cengage Learning Soil Profile • Cross-sectional view of the different layers or horizons in soil • Undisturbed soil will have four or more horizons in its profile – O horizon: on surface and composed of organic matter and small amount of mineral matter © 2009 Delmar, Cengage Learning Soil Profile – A horizon: topsoil; located near surface and combination of mineral matter and organic matter – B horizon: subsoil; similar to A horizon but particle size and proportions differ; less organic material – C horizon: parent material, large soil particles – How many layers do you see in this picture? © 2009 Delmar, Cengage Learning Properties of Soil • A variety of physical properties of soil exist – – – – – – slope: angle of soil surface texture: proportions of sand, silt, and clay drainage: how well water flows through soil flood hazard: likelihood area will flood erosion: degree soil is damaged by erosion topsoil and subsoil thickness: layer depths © 2009 Delmar, Cengage Learning Soil and Plants • Soil provides individual plants with four basic needs – – – – anchorage water oxygen nutrients © 2009 Delmar, Cengage Learning Soil Uses • Human societies depend on soil for – – – – – – – cropland grazing land urbanization building waste disposal forests recreation © 2009 Delmar, Cengage Learning Human Uses of Soil • Cropland – land where crops are planted, cared for, and harvested – Two basic types of crops: annual and perennial © 2009 Delmar, Cengage Learning Human Uses of Soil • Annual crops – – – – planted and harvested within one growing season requires yearly preparation of soil prone to erosion corn, soybeans, cotton, vegetables • Perennial crops – remain in ground several years – alfalfa, fruits, nuts, and nursery stock © 2009 Delmar, Cengage Learning Human Uses of Soil • Grazing land – used to feed grazing animals such as cattle and sheep – eastern United States uses pastures planted with perennial forage – western United States uses rangeland of native grasses © 2009 Delmar, Cengage Learning Human Uses of Soil • Urbanization – land used to build cities, towns, factories, and roads – continues to grow at expense of other land uses © 2009 Delmar, Cengage Learning Human Uses of Soil • Buildings – land used to prepare foundations for construction • Several properties of soil are considered, including – shrink-swell potential – load-bearing capacity © 2009 Delmar, Cengage Learning Human Uses of Soil • Shrink-swell potential – how much soil swells when wet and shrinks when dry • Load-bearing capacity – ability of soil to support great weight © 2009 Delmar, Cengage Learning Human Uses of Soil • Waste disposal – using soil to filter, contain, or confine waste – waste disposal takes a variety of forms • sanitary landfills • hazardous waste landfills • personal home septic systems © 2009 Delmar, Cengage Learning Human Uses of Soil • Forests – soil often left undisturbed – harvesting of trees can damage soil • tear up vegetation • compact soil – may result in increased erosion or limited growth potential © 2009 Delmar, Cengage Learning Human Uses of Soil • Recreation – also takes a variety of forms • golf courses, playing fields, parks, campgrounds – may require special construction or management © 2009 Delmar, Cengage Learning A Living Environment • Soil is living medium containing great variety of organisms – amphibians, mammals, insects, reptiles, worms, microbes, etc. • Most diverse ecosystem on Earth • Many organisms in soil are decomposers © 2009 Delmar, Cengage Learning A Living Environment • Decomposers – break down material that was once living – decomposers play irreplaceable role © 2009 Delmar, Cengage Learning Erosion • Natural process forming channels and canyons – However, human activity is accelerating the process © 2009 Delmar, Cengage Learning Erosion • Major environmental issue – Each year, almost 2 billion tons of soil lost • mostly result of water erosion – Approximately 21 percent of U.S. cropland suffers excessive soil losses – We must conserve soil resources by reducing or eliminating erosion losses © 2009 Delmar, Cengage Learning Erosion by Water • Water erosion occurs in three steps – detachment – transport – deposition © 2009 Delmar, Cengage Learning Erosion by Water • Factors affecting rate of erosion – – – – – soil texture and structure organic matter content slope soil cover plant cover © 2009 Delmar, Cengage Learning Erosion by Wind • Accounts for 40 percent of soil loss in United States • Dry areas with high winds are most prone to wind erosion • Bare soil is at greatest risk © 2009 Delmar, Cengage Learning Erosion by Wind • Effects of wind erosion – – – – – – Removes topsoil reduces nutrient- and water-holding capacities “sandblasts” young plants fills in road or drainage ditches affects respiratory health of humans and other animals wears down paint and other surfaces © 2009 Delmar, Cengage Learning Preventing and Controlling Erosion • Two key practices in controlling erosion – protecting soil surfaces – slowing movement of water and wind © 2009 Delmar, Cengage Learning Preventing and Controlling Erosion • Soil conservation must be practiced to preserve our soil resources – Implementation of best management practices must become a priority – A wide variety of management practices exist to help control erosion © 2009 Delmar, Cengage Learning
