Elements of the Nature and Properties of Soils Pearson New International Edition 9 781292 039299 ISBN 978 1 29203 929 9 Elements of the Nature and Properties of Soils Nyle C Brady Raymond Weil Third E[.]
9 781292 039299 Elements of the Nature and Properties of Soils Brady 3e ISBN 978-1-29203-929-9 Elements of the Nature and Properties of Soils Nyle C Brady Raymond Weil Third Edition Pearson New International Edition Elements of the Nature and Properties of Soils Nyle C Brady Raymond Weil Third Edition Pearson Education Limited Edinburgh Gate Harlow Essex CM20 2JE England and Associated Companies throughout the world Visit us on the World Wide Web at: www.pearsoned.co.uk © Pearson Education Limited 2014 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without either the prior written permission of the publisher or a licence permitting restricted copying in the United Kingdom issued by the Copyright Licensing Agency Ltd, Saffron House, 6–10 Kirby Street, London EC1N 8TS All trademarks used herein are the property of their respective owners The use of any trademark in this text does not vest in the author or publisher any trademark ownership rights in such trademarks, nor does the use of such trademarks imply any affiliation with or endorsement of this book by such owners ISBN 10: 1-292-03929-9 ISBN 10: 1-269-37450-8 ISBN 13: 978-1-292-03929-9 ISBN 13: 978-1-269-37450-7 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Printed in the United States of America P E A R S O N C U S T O M L I B R A R Y Table of Contents Glossary of Soil Science Terms Nyle C Brady/Ray R Weil 1 The Soils Around Us Nyle C Brady/Ray R Weil 21 Formation of Soils from Parent Materials Nyle C Brady/Ray R Weil 49 Soil Classification Nyle C Brady/Ray R Weil 85 Soil Architecture and Physical Properties Nyle C Brady/Ray R Weil 131 Soil Water: Characteristics and Behavior Nyle C Brady/Ray R Weil 173 Soil and the Hydrologic Cycle Nyle C Brady/Ray R Weil 209 Soil Aeration and Temperature Nyle C Brady/Ray R Weil 247 The Colloidal Fraction: Seat of Soil Chemical and Physical Activity Nyle C Brady/Ray R Weil 285 Soil Acidity, Alkalinity, Aridity, and Salinity Nyle C Brady/Ray R Weil 321 10 Organisms and Ecology of the Soil Nyle C Brady/Ray R Weil 379 11 Soil Organic Matter Nyle C Brady/Ray R Weil 421 12 Nutrient Cycles and Soil Fertility Nyle C Brady/Ray R Weil 457 I 13 Practical Nutrient Management Nyle C Brady/Ray R Weil 521 14 Soil Erosion and Its Control Nyle C Brady/Ray R Weil 567 15 Soils and Chemical Pollution II Nyle C Brady/Ray R Weil 605 Appendix: World Reference Base, Canadian, and Australian Soil Classification Systems Nyle C Brady/Ray R Weil 637 Appendix: SI Units, Conversion Factors, Periodic Table of the Elements, and Plant Names Nyle C Brady/Ray R Weil 643 Global Soil Regions Nyle C Brady/Ray R Weil 649 Index 653 Glossary of Soil Science Terms1 The surface horizon of a mineral soil having maximum organic matter accumulation, maximum biological activity, and/or eluviation of materials such as iron and aluminum oxides and silicate clays A horizon abiotic Nonliving basic elements of the environment, such as rainfall, temperature, wind, and minerals Erosion much more rapid than normal, natural, geological erosion; primarily as a result of the activities of humans or, in some cases, of animals accelerated erosion Cations, principally Al3+, Fe3+, and H+, that contribute to H+ ion activity either directly or through hydrolysis reactions with water See also non-acid cations acid cations Atmospheric precipitation with pH values less than about 5.6, the acidity being due to inorganic acids (such as nitric and sulfuric) that are formed when oxides of nitrogen and sulfur are emitted into the atmosphere acid rain The proportion or percentage of a cation-exchange site occupied by acid cations acid saturation A soil with a pH value 7.0 Usually applied to surface layer or root zone, but may be used to characterize any horizon See also reaction, soil acid soil Soils that are potentially extremely acid (pH 3.5) because of the presence of large amounts of reduced forms of sulfur that are oxidized to sulfuric acid if the soils are exposed to oxygen when they are drained or excavated A sulfuric horizon containing the yellow mineral jarosite is often present See also cat clays acid sulfate soils acidity, active The activity of hydrogen ions in the aqueous phase of a soil It is measured and expressed as a pH value acidity, residual Soil acidity that can be neutralized by lime or other alkaline materials but cannot be replaced by an unbuffered salt solution somewhat similar in appearance, to fungal hyphae Includes many members of the order Actinomycetales The upper portion of a Gelisol that is subject to freezing and thawing and is underlain by permafrost active layer active organic matter A portion of the soil organic matter that is relatively easily metabolized by microorganisms and cycles with a half-life in the soil of a few days to a few years adhesion Molecular attraction that holds the surfaces of two substances (e.g., water and sand particles) in contact The attraction of ions or compounds to the surface of a solid Soil colloids adsorb large amounts of ions and water adsorption adsorption complex The group of organic and inorganic substances in soil capable of adsorbing ions and molecules aeration, soil The process by which air in the soil is replaced by air from the atmosphere In a well-aerated soil, the soil air is similar in composition to the atmosphere above the soil Poorly aerated soils usually contain more carbon dioxide and correspondingly less oxygen than the atmosphere above the soil (1) Having molecular oxygen as a part of the environment (2) Growing only in the presence of molecular oxygen, as aerobic organisms (3) Occurring only in the presence of molecular oxygen (said of certain chemical or biochemical processes, such as aerobic decomposition) aerobic aerosolic dust A type of eolian material that is very fine (about to 10 µm) and may remain suspended in the air over distances of thousands of kilometers Finer than most loess Many soil particles held in a single mass or cluster, such as a clod, crumb, block, or prism aggregate (soil) Exchangeable hydrogen and aluminum that can be replaced from an acid soil by an unbuffered salt solution such as KCl or NaCl A diagnostic subsurface horizon in which clay, silt, and humus derived from an overlying cultivated and fertilized layer have accumulated Wormholes and illuvial clay, silt, and humus occupy at least 5% of the horizon by volume The total acidity in a soil It is approximated by the sum of the salt-replaceable acidity plus the residual acidity agroforestry Any type of multiple cropping land-use that entails complementary relations between trees and agricultural crops A group of bacteria that form branched mycelia that are thinner, but agronomy A specialization of agriculture concerned with the theory and practice of acidity, salt replaceable acidity, total Actinomycetes agric horizon field-crop production and soil management The scientific management of land The proportion of the bulk volume of soil that is filled with air at any given time or under a given condition, such as a specified moisture potential; usually the large pores air porosity A diagnostic subsurface horizon from which clay and free iron oxides have been removed or in which the oxides have been segregated to the extent that the color of the horizon is determined primarily by the color of the primary sand and silt particles rather than by coatings on these particles albic horizon Alfisols An order in Soil Taxonomy Soils with gray to brown surface horizons, medium to high supply of bases, and B horizons of illuvial clay accumulation These soils form mostly under forest or savanna vegetation in climates with slight to pronounced seasonal moisture deficit A population explosion of algae in surface waters, such as lakes and streams, often resulting in high turbidity and green- or red-colored water, and commonly stimulated by nutrient enrichment with phosphorus and nitrogen algal bloom alkaline soil Any soil that has pH 77 Usually applied to the surface layer or root zone but may be used to characterize any horizon or a sample thereof See also reaction, soil allelochemical An organic chemical by which one plant can influence another See allelopathy allelopathy The process by which one plant may affect other plants by biologically active chemicals introduced into the soil, either directly by leaching or exudation from the source plant, or as a result of the decay of the plant residues The effects, though usually negative, may also be positive allophane A poorly defined aluminosilicate mineral whose structural framework consists of short runs of three-dimensional crystals interspersed with amorphous noncrystalline materials Along with its more weathered companion, it is prevalent in volcanic ash materials Fan-shaped alluvium deposited at the mouth of a canyon or ravine where debrisladen waters fan out, slow down, and deposit their burden alluvial fan 1This glossary was compiled and modified from several sources, including Glossary of Soil Science Terms [Madison, WI: Soil Science Society of America (1997)], Resource Conservation Glossary [Ankeny, IA: Soil Conservation Society of America (1982)], and Soil Taxonomy [Washington, DC: U.S Department of Agriculture (1999)] From the Glossary of Elements of the Nature and Properties of Soils, Third Edition, Nyle C Brady, Ray R Weil Copyright © 2010 by Pearson Education, Inc Published by Pearson Prentice Hall All rights reserved glossary alluvium A general term for all detrital material deposited or in transit by streams, including gravel, sand, silt, clay, and all variations and mixtures of these Unless otherwise noted, alluvium is unconsolidated anion exchange capacity The sum total of exchangeable anions that a soil can adsorb Expressed as centimoles of charge per kilogram (cmolc /kg) of soil (or of other adsorbing material, such as clay) Compounds containing aluminum, silicon, and oxygen as main constituents An example is microcline, KAlSi3O8 anoxic aluminosilicates amendment, soil Any substance other than fertilizers, such as lime, sulfur, gypsum, and sawdust, used to alter the chemical or physical properties of a soil, generally to make it more productive Nitrogen-containing organic acids that couple together to form proteins Each acid molecule contains one or more amino groups (—NH2) and at least one carboxyl group (—COOH) In addition, some amino acids contain sulfur amino acids A biochemical process in the N cycle by which certain anaerobic bacteria or archaea oxidize ammonium ions using nitrite ions as the electron acceptor, the main product being N2 gas Ammanox The biochemical process whereby ammoniacal nitrogen is released from nitrogen-containing organic compounds ammonification The entrapment of ammonium ions by the mineral or organic fractions of the soil in forms that are insoluble in water and are at least temporarily nonexchangeable ammonium fixation amorphous material Noncrystalline con- stituents of soils (1) The absence of molecular oxygen (2) Growing or occurring in the absence of molecular oxygen (e.g., anaerobic bacteria or biochemical reduction reaction) anaerobic anaerobic respiration The metabolic process whereby electrons are transferred from a reduced compound (usually organic) to an inorganic acceptor molecule other than oxygen Soil properties related to volcanic origin of materials, including high organic carbon content, low bulk density, high phosphate retention, and extractable iron and aluminum andic properties An order in Soil Taxonomy Soils of dry climates They have pedogenic horizons, low in organic matter, that are never moist for as long as three consecutive months They have an ochric epipedon and one or more of the following diagnostic horizons: argillic, natric, cambic, calcic, petrocalcic, gypsic, petrogypsic, salic, or a duripan anthropic epipedon A diagnostic surface horizon of mineral soil that has the same requirements as the mollic epipedon but that has more than 250 mg/kg of P2O5 soluble in 1% citric acid, or is dry more than 10 months (cumulative) during the period when not irrigated The anthropic epipedon forms under long-continued cultivation and fertilization Aridisols A substance produced by one species of organism that, in low concentrations, will kill or inhibit growth of certain other organisms aspect (of slopes) The direction (e.g., south or north) that a slope faces with respect to the sun Ap The surface layer of a soil disturbed by cultivation or pasturing Atterberg limits antibiotic apatite A naturally occurring complex calcium phosphate that is the original source of most of the phosphate fertilizers Formulas such as [3Ca3(PO4)2] · CaF2 illustrate the complex compounds that make up apatite aquic conditions Continuous or periodic saturation (with water) and reduction, commonly indicated by redoximorphic features A saturated body of rock or sediment that is incapable of transmitting significant quantities of water under ordinary water pressures aquiclude aquifer A saturated, permeable layer of sediment or rock that can transmit significant quantities of water under normal pressure conditions Specialized branched structure formed within a root cortical cell by endotrophic mycorrhizal fungi arbuscule arbuscular mycorrhiza A common endomycorrhizal association produced by phycomycetous fungi and characterized by the development, within root cells, of small structures known as arbuscules Some also form, between root cells, storage organs known as vesicles Host range includes many agricultural and horticultural crops Formerly called vesicular arbuscular mycorrhiza (VAM) See also endotrophic mycorrhiza association, soil See soil association Water contents of finegrained soils at different states of consistency liquid limit (LL) The water content corresponding to the arbitrary limit between the liquid and plastic states of consistency of a soil plastic limit (PL) The water content corresponding to an arbitrary limit between the plastic and semisolid states of consistency of a soil autochthonous organisms Those microorganisms thought to subsist on the more resistant soil organic matter and little affected by the addition of fresh organic materials Contrast with zymogenous organisms See also k-strategist autotroph An organism capable of utilizing carbon dioxide or carbonates as the sole source of carbon and obtaining energy for life processes from the oxidation of inorganic elements or compounds such as iron, sulfur, hydrogen, ammonium, and nitrites, or from radiant energy Contrast with heterotroph available nutrient That portion of any element or compound in the soil that can be readily absorbed and assimilated by growing plants (“Available” should not be confused with “exchangeable.”) Archaea The maximum slope steepness at which loose, cohesionless material will come to rest One of the two domains of singlecelled prokaryote microorganisms Includes organisms adapted to extremes of salinity and heat, and those that subsist on methane Similar appearing, but evolutionarily distinct from bacteria The portion of water in a soil that can be readily absorbed by plant roots The amount of water released between the field capacity and the permanent wilting point anion Negatively charged ion; during electrolysis it is attracted to the positively charged anode argillan A thin coating of well-oriented clay particles on the surface of a soil aggregate, particle, or pore A clay film B horizon A soil horizon, usually beneath the A or E horizon, that is characterized by one or more of the following: (1) a concentration of soluble salts, silicate clays, iron and aluminum oxides, and humus, alone or in combination; (2) a blocky or prismatic structure; and (3) coatings of iron and aluminum oxides that give darker, stronger, or redder color Exchange of anions in the soil solution for anions adsorbed on the surface of clay and humus particles argillic horizon An order in Soil Taxonomy Soils developed from volcanic ejecta The colloidal fraction is dominated by allophane and/or Al-humus compounds Andisols angle of repose anion exchange See anaerobic Climate in regions that lack sufficient moisture for crop production without irrigation In cool regions annual precipitation is usually less than 25 cm It may be as high as 50 cm in tropical regions Natural vegetation is desert shrubs arid climate A diagnostic subsurface horizon characterized by the illuvial accumulation of layer-lattice silicate clays available water One of two domains of singlecelled prokaryote microorganisms Includes all that are not Archaea Bacteria glossary A unit of pressure equal to million dynes per square centimeter (106 dynes/cm2) It approximates the pressure of a standard atmosphere bar Cations that form strong (strongly dissociated) bases by reaction with hydroxyl; e.g., K+ forms potassium hydroxide (K+ + OH) See non-acid cations base-forming cations (obsolete) The extent to which the adsorption complex of a soil is saturated with exchangeable cations other than hydrogen and aluminum It is expressed as a percentage of the total cation exchange capacity See non-acid saturation base saturation percentage The solid rock underlying soils and the regolith in depths ranging from zero (where exposed by erosion) to several hundred feet bedrock An embankment constructed across sloping fields with a steep drop on the downslope side bench terrace A buildup within an organism of specific compounds due to biological processes Commonly applied to heavy metals, pesticides, or metabolites bioaccumulation The cleanup of contaminated soils by adding exotic microorganisms that are especially efficient at breaking down an organic contaminant A form of bioremediation bioaugmentation biodegradable Subject to degradation by biochemical processes Occurs at ordinary temperatures and pressures It is commonly carried out by certain bacteria, algae, and actinomycetes, which may or may not be associated with higher plants biological nitrogen fixation biomass The total mass of living material of a specified type (e.g., microbial biomass) in a given environment (e.g., in a cubic meter of soil) biopores Soil pores, usually of relatively large diameter, created by plant roots, earthworms, or other soil organisms The decontamination or restoration of polluted or degraded soils by means of enhancing the chemical degradation or other activities of soil organisms bioremediation A group of related soils that differ, one from the other, primarily because of differences in kinds and numbers of plants and soil organisms as a soil-forming factor biosequence Sewage sludge that meets certain regulatory standards, making it suitable for land application See sewage sludge biosolids The cleanup of contaminated soils through the manipulation of nutrients or other soil environmental factors to enhance the activity of naturally occurring soil microorganisms A form of bioremediation biostimulation Soil aggregates with blocklike shapes; common in B horizons of soils in humid regions blocky soil structure A low embankment with such gentle slopes that it can be farmed, constructed across sloping fields to reduce erosion and runoff broad-base terrace broadcast Scatter seed or fertilizer on the surface of the soil Abandoned, idled, or underused industrial and commercial facilities where expansion or redevelopment is complicated by real or perceived environmental contamination brownfields The ability of a soil to resist changes in pH Commonly determined by presence of clay, humus, and other colloidal materials buffering capacity The mass of dry soil per unit of bulk volume, including the air space The bulk volume is determined before drying to constant weight at 105 °C bulk density, soil Soil covered by an alluvial, loessal, or other deposit, usually to a depth greater than the thickness of the solum buried soil by-pass flow See preferential flow A mineral horizon, generally beneath the solum, that is relatively unaffected by biological activity and pedogenesis and is lacking properties diagnostic of an A or B horizon It may or may not be like the material from which the A and B have formed C horizon Soil containing sufficient calcium carbonate (often with magnesium carbonate) to effervesce visibly when treated with cold 0.1 N hydrochloric acid calcareous soil calcic horizon A diagnostic subsurface horizon of secondary carbonate enrichment that is more than 15 cm thick, has a calcium carbonate equivalent of more than 15%, and has at least 5% more calcium carbonate equivalent than the underlying C horizon A layer near the surface, more or less cemented by secondary carbonates of calcium or magnesium precipitated from the soil solution It may occur as a soft, thin soil horizon; as a hard, thick bed just beneath the solum; or as a surface layer exposed by erosion caliche A diagnostic subsurface horizon that has a texture of loamy very fine sand or finer, contains some weatherable minerals, and is characterized by the alteration or removal of mineral material The cambic horizon lacks cementation or induration and has too few evidences of illuviation to meet the requirements of the argillic or spodic horizon cambic horizon A zone in the soil just above the plane of zero water pressure (water table) that remains saturated or almost saturated with water capillary fringe capillary water The water held in the capillary or small pores of a soil, usually with a tension 760 cm of water See also soil water potential carbon cycle The sequence of transformations whereby carbon dioxide is fixed in living organisms by photosynthesis or by chemosynthesis, liberated by respiration and by the death and decomposition of the fixing organism, used by heterotrophic species, and ultimately returned to its original state carbon/nitrogen (C/N) ratio The ratio of the weight of organic carbon (C) to the weight of total nitrogen (N) in a soil or in organic material carnivore An organism that feeds on animals Rounded, water-stable aggregates of soil that have passed through the gut of an earthworm casts, earthworm catena A group of soils that commonly occur together in a landscape, each characterized by a different slope position and resulting set of drainage-related proprieties See also toposequence cation A positively charged ion; during electrolysis it is attracted to the negatively charged cathode cation exchange The interchange between a cation in solution and another cation on the surface of any surface-active material, such as clay or organic matter cation exchange capacity The sum total of exchangeable cations that a soil can adsorb Sometimes called total exchange capacity, base exchange capacity, or cation adsorption capacity Expressed in centimoles of charge per kilogram (cmolc /kg) of soil (or of other adsorbing material, such as clay) Indurated; having a hard, brittle consistency because the particles are held together by cementing substances, such as humus, calcium carbonate, or the oxides of silicon, iron, and aluminum cemented Thin, flat fragments of limestone, sandstone, or schist up to 15 cm (6 in.) in major diameter channery (Greek “claw”) A type of chemical compound in which a metallic ion is firmly combined with an organic molecule by means of multiple chemical bonds chelate chert A structureless form of silica, closely related to flint, that breaks into angular fragments chisel, subsoil A tillage implement with one or more cultivator-type feet to which are attached strong knifelike units used to shatter or loosen hard, compact layers, usually in the subsoil, to depths below normal plow depth See also subsoiling glossary chlorite A 2:1:1-type layer-structured silicate mineral having 2:1 layers alternating with a magnesium-dominated octahedral sheet A condition in plants relating to the failure of chlorophyll (the green coloring matter) to develop Chlorotic leaves range from light green through yellow to almost white chlorosis chroma (color) See Munsell color system A sequence of related soils that differ, one from the other, in certain properties primarily as a result of time as a soilforming factor chronosequence classification, soil See soil classification (1) A soil separate consisting of particles 60.002 mm in equivalent diameter (2) A soil textural class containing 740% clay, 45% sand, and 640% silt clay clay mineral Naturally occurring inorganic material (usually crystalline) found in soils and other earthy deposits, the particles being of clay size, that is, 60.002 mm in diameter claypan A dense, compact, slowly permeable layer in the subsoil having a much higher clay content than the overlying material, from which it is separated by a sharply defined boundary Claypans are usually hard when dry and plastic and sticky when wet See also hardpan A group of related soils that differ, one from another, primarily because of differences in climate as a soil-forming factor climosequence A compact, coherent mass of soil produced artificially, usually by such human activities as plowing and digging, especially when these operations are performed on soils that are either too wet or too dry for normal tillage operations clod Mineral (rock) soil particles larger than mm in diameter Compare to fine earth fraction coarse fragments coarse texture The texture exhibited by sands, loamy sands, and sandy loams (except very fine sandy loam) Rounded or partially rounded rock or mineral fragments 7.5 to 25 cm (3 to 10 in.) in diameter cobblestone A method of composting in which two materials of differing but complementary nature are mingled together and enhance each other’s decomposition in a compost system co-composting Holding together: Force holding a solid or liquid together, owing to attraction between like molecules Decreases with rise in temperature cohesion Certain soil that may undergo a sudden loss in strength when wetted collapsible soil colloid, soil (Greek “gluelike”) Organic and inorganic matter with very small particle size and a correspondingly large surface area per unit of mass close-growing crops, or fallow are alternated with those of cultivated crops colluvium A deposit of rock fragments and soil material accumulated at the base of steep slopes as a result of gravitational action controlled traffic A farming system in which all wheeled traffic is confined to fixed paths so that repeated compaction of the soil does not occur outside the selected paths The property of an object that depends on the wavelength of light it reflects or emits color columnar soil structure See soil structure types convection The transfer of heat through a gas or solution because of molecular movement A close-growing crop grown primarily for the purpose of protecting and improving soil between periods of regular crop production or between trees and vines in orchards and vineyards cover crop The practice of growing certain species of plants in close proximity because one species has the effect of improving the growth of the other, sometimes by positive allelopathic effects companion planting Organic residues, or a mixture of organic residues and soil, that have been piled, moistened, and allowed to undergo biological decomposition Mineral fertilizers are sometimes added Usually managed so as to reach thermophilic temperatures compost creep Slow mass movement of soil and soil material down relatively steep slopes, primarily under the influence of gravity, but facilitated by saturation with water and by alternate freezing and thawing concretion A planned sequence of crops growing in a regularly recurring succession on the same area of land, as contrasted to continuous culture of one crop or growing different crops in haphazard order The transfer of heat by physical contact between two or more objects crotovina A former animal burrow in one soil horizon that has been filled with organic matter or material from another horizon (also spelled krotovina) A local concentration of a chemical compound, such as calcium carbonate or iron oxide, in the form of grains or nodules of varying size, shape, hardness, and color conduction conductivity, hydraulic See hydraulic conductivity A soft, porous, more or less rounded natural unit of structure from to mm in diameter See also soil structure types crumb conservation tillage See tillage, conservation consistence The combination of properties of soil material that determine its resistance to crushing and its ability to be molded or changed in shape Such terms as loose, friable, firm, soft, plastic, and sticky describe soil consistence The interaction of adhesive and cohesive forces within a soil at various moisture contents as expressed by the relative ease with which the soil can be deformed or ruptured consistency consociation crop rotation See soil consociation consolidation test A laboratory test in which a soil mass is laterally confined within a ring and is compressed with a known force between two porous plates constant charge The net surface charge of mineral particles, the magnitude of which depends only on the chemical and structural composition of the mineral The charge arises from isomorphous substitution and is not affected by soil pH The water used by plants in transpiration and growth, plus water vapor loss from adjacent soil or snow, or from intercepted precipitation in any specified time Usually expressed as equivalent depth of free water per unit of time consumptive use contour strip-cropping Layout of crops in comparatively narrow strips in which the farming operations are performed approximately on the contour Usually strips of grass, crushing strength The force required to crush a mass of dry soil or, conversely, the resistance of the dry soil mass to crushing Expressed in units of force per unit area (pressure) crust (soil) (1) physical A surface layer on soils, ranging in thickness from a few millimeters to as much as cm, that physicalchemical processes have caused to be much more compact, hard, and brittle when dry than the material immediately beneath it (2) microbiotic An assemblage of cyanobacteria, algae, lichens, liverworts, and mosses that commonly forms an irregular crust on the soil surface, especially on otherwise barren, arid-region soils Also referred to as cryptogamic, cryptobiotic, or biological crusts cryophilic Pertaining to low temperatures in the range of to 15 °C, the range in which cryophilic organisms grow best Physical disruption and displacement of soil material within the profile by the forces of freezing and thawing Sometimes called frost churning, it results in irregular, broken horizons, involutions, oriented rock fragments, and accumulation of organic matter on the permafrost table cryoturbation cryptogam See crust (2) microbiotic glossary crystal A homogeneous inorganic substance of definite chemical composition bounded by planar surfaces that form definite angles with each other, thus giving the substance a regular geometrical form The orderly arrangement of atoms in a crystalline material crystal structure cultivation A tillage operation used in preparing land for seeding or transplanting or later for weed control and for loosening the soil A modification of the texture, structure, or fabric at natural surfaces in soil materials due to concentration of particular soil constituents; e.g “clay skins.” cutans Chlorophyll-containing bacteria that accommodate both photosynthesis and nitrogen fixation Formerly called bluegreen algae cyanobacteria deciduous plant A plant that sheds all its leaves every year at a certain season Chemical breakdown of a compound (e.g., a mineral or organic compound) into simpler compounds, often accomplished with the aid of microorganisms decomposition deflocculate (1) To separate the individual components of compound particles by chemical and/or physical means (2) To cause the particles of the disperse phase of a colloidal system to become suspended in the dispersion medium An individual polygon shown by a closed boundary on a soil map that defines the area, shape, and location of a map unit within a landscape delineation desorption The removal of sorbed material from surfaces detritivore An organism that subsists on detritus detritus (As used in Soil Taxonomy) Horizons having specific soil characteristics that are indicative of certain classes of soils Horizons that occur at the soil surface are called epipedons; those below the surface, diagnostic subsurface horizons diagnostic horizons diatomaceous earth A geologic deposit of fine, grayish, siliceous material composed chiefly or wholly of the remains of diatoms It may occur as a powder or as a porous, rigid material Algae having siliceous cell walls that persist as a skeleton after death; any of the microscopic unicellular or colonial algae constituting the class Bacillariaceae They occur abundantly in fresh and salt waters and their remains are widely distributed in soils diatoms The movement of atoms in a gaseous mixture or of ions in a solution, primarily as a result of their own random motion diffusion An octahedral sheet of silicate clays in which the sites for the sixcoordinated metallic atoms are mostly filled with trivalent atoms, such as A13+ dioctahedral sheet disintegration Physical or mechanical breakup or separation of a substance into its component parts (e.g., a rock breaking into its mineral components) (1) To break up compound particles, such as aggregates, into the individual component particles (2) To distribute or suspend fine particles, such as clay, in or throughout a dispersion medium, such as water delta An alluvial deposit formed where a stream or river drops its sediment load upon entering a quieter body of water dissimilatory nitrate reduction to ammonium (DNRA) A bacterial process by which The biochemical reduction of nitrate or nitrite to gaseous nitrogen, either as molecular nitrogen or as an oxide of nitrogen denitrification density See particle density; bulk density disperse nitrate is converted to ammonium under a wide range of oxygen and carbon levels Compare to dentrification (a different type of dissimilatory nitrate reduction) which is strictly anaerobic and requires an energy source Process by which molecules of a gas, solid, or another liquid dissolve in a liquid, thereby becoming completely and uniformly dispersed throughout the liquid’s volume desalinization dissolution desert crust A hard layer, containing calcium carbonate, gypsum, or other binding material, exposed at the surface in desert regions distribution coefficient (Kd) Removal of salts from saline soil, usually by leaching A natural residual concentration of closely packed pebbles, boulders, and other rock fragments on a desert surface where wind and water action has removed all smaller particles desert pavement A thin, dark, shiny film or coating of iron oxide and lesser amounts of manganese oxide and silica formed on the surfaces of pebbles, boulders, rock fragments, and rock outcrops in arid regions desert varnish Material of any sort deposited by geological processes in one place after having been removed from another Glacial drift includes material moved by the glaciers and by the streams and lakes associated with them drift Debris from dead plants and animals The ratio of eroded sediment carried out of a drainage basin to the total amount of sediment moved within the basin by erosion processes delivery ratio drainage, soil The frequency and duration of periods when the soil is free from saturation with water The distribution of a chemical between soil and water diversion terrace See terrace (1) To provide channels, such as open ditches or drain tile, so that excess water can be removed by surface or by internal flow (2) To lose water (from the soil) by percolation drain An area of soil into which the effluent from a septic tank is piped so that it will drain through the lower part of the soil profile for disposal and purification drain field, septic tank drumlin Long, smooth, cigar-shaped low hills of glacial till, with their long axes parallel to the direction of ice movement dryland farming The practice of crop production in low-rainfall areas without irrigation duff The matted, partly decomposed organic surface layer of forest soils A diagnostic subsurface horizon that is cemented by silica, to the point that airdry fragments will not slake in water or HCl Hardpan duripan dust mulch A loose, finely granular or powdery condition on the surface of the soil, usually produced by shallow cultivation Horizon characterized by maximum illuviation (washing out) of silicate clays and iron and aluminum oxides; commonly occurs above the B horizon and below the A horizon E horizon earthworms Animals of the Lumbricidae family that burrow into and live in the soil They mix plant residues into the soil and improve soil aeration ecosystem A dynamic and interacting combination of all the living organisms and nonliving elements (matter and energy) of an area Products of natural ecosystems that support and fulfill the needs of human beings Provision of clean water and unpolluted air are examples ecosystem services ectotrophic mycorrhiza (ectomycorrhiza) A symbiotic association of the mycelium of fungi and the roots of certain plants in which the fungal hyphae form a compact mantle on the surface of the roots and extend into the surrounding soil and inward between cortical cells, but not into these cells Associated primarily with certain trees See also endotrophic mycorrhiza edaphology The science that deals with the influence of soils on living things, particularly plants, including human use of land for plant growth The amount of cation charges that a material (usually soil or soil colloids) can hold at the pH of the material, measured as the sum of the exchangeable Al3+, Ca2+, Mg2+, K+, and Na+, and expressed as moles or cmol of charge per kg of material See also cation exchange capacity effective cation exchange capacity .. .Pearson New International Edition Elements of the Nature and Properties of Soils Nyle C Brady Raymond Weil Third Edition Pearson Education Limited Edinburgh Gate Harlow Essex CM20 2JE England... Department of Agriculture (1999)] From the Glossary of Elements of the Nature and Properties of Soils, Third Edition, Nyle C Brady, Ray R Weil Copyright © 2010 by Pearson Education, Inc Published by Pearson. .. cryoturbation and/ or ice in the form of lenses, veins, or wedges and the like The mode of origin of the soil, with special reference to the processes responsible for the development of the solum,