Man Soil Qual

Managing Soil Quality

Challenges in Modern Agriculture

Edited by

P. Schjnning, S. Elmholt and B.T. Christensen

Danish Institute of Agricultural SciencesResearch Centre Foulum

TjeleDenmark

CABI Publishing

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A catalogue record for this book is available from the British Library, London,UK.

Library of Congress Cataloging-in-Publication DataManaging soil quality : challenges in modern agriculture / edited by P.Schjonning, S. Elmholt, and B.T. Christensen.

p. cm.Includes bibliographical references and index.

ISBN 0-85199-671-X (alk paper)1. Soils--Quality. 2. Soil management. I. Schjonning, P. (Per) II.

Elmholt, S. (Susanne) III. Christensen, B. T. (Bent Tolstrup)

S591.M323 2004631.4--dc21 2003008927

ISBN 0 85199 671 X

Typeset by AMA DataSet, UKPrinted and bound in the UK by Biddles Ltd, Kings Lynn



Contents

Contributors v

Preface vii

1. Soil Quality Management Concepts and Terms 1P. Schjnning, S. Elmholt and B.T. Christensen

2. Soil Quality, Fertility and Health Historical Context, Status and Perspectives 17D.L. Karlen, S.S. Andrews and B.J. Wienhold

3. Soil Acidity Resilience and Thresholds 35A.E. Johnston

4. Tightening the Nitrogen Cycle 47B.T. Christensen

5. Phosphorus Surplus and Deficiency 69L.M. Condron

6. Sustainable Management of Potassium 85M. Askegaard, J. Eriksen and A.E. Johnston

7. Developing and Maintaining Soil Organic Matter Levels 103W.A. Dick and E.G. Gregorich

8. Microbial Diversity in Soil Effects on Crop Health 121C. Alabouvette, D. Backhouse, C. Steinberg, N.J. Donovan, V. Edel-Hermann andL.W. Burgess

9. Biological Soil Quality from Biomass to Biodiversity Importance andResilience to Management Stress and Disturbance 139L. Brussaard, T.W. Kuyper, W.A.M. Didden, R.G.M. de Goede and J. Bloem

10. Subsoil Compaction and Ways to Prevent It 163J.J.H. Van den Akker and P. Schjnning

iii

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11. Management-induced Soil Structure Degradation Organic Matter Depletionand Tillage 185B.D. Kay and L.J. Munkholm

12. Soil Erosion Processes, Damages and Countermeasures 199G. Govers, J. Poesen and D. Goossens

13. Recyclable Urban and Industrial Waste Benefits and Problems inAgricultural Use 219R. Naidu, M. Megharaj and G. Owens

14. Pesticides in Soil Benefits and Limitations to Soil Health 239M.A. Locke and R.M. Zablotowicz

15. Systems Approaches for Improving Soil Quality 261M.R. Carter, S.S. Andrews and L.E. Drinkwater

16. Implementing Soil Quality Knowledge in Land-use Planning 283J. Bouma

17. Soil Quality in Industrialized and Developing Countries Similaritiesand Differences 297R. Lal

18. Soil Quality Management Synthesis 315P. Schjnning, S. Elmholt and B.T. Christensen

Index 335

iv Contents



Contributors

Alabouvette, C., CMSE-INRA, U.M.R. Biochimie, Biologie Cellulaire et Ecologie des InteractionsPlantes Microorganismes, F 21065 Dijon, France.

Andrews, S.S., USDA-NRCS, Soil Quality Institute, 2150 Pammel Drive, Ames, Iowa 50011, USA.Askegaard, M., Danish Institute of Agricultural Sciences, Department of Agroecology, PO Box 50,

DK-8830 Tjele, Denmark.Backhouse, D., University of New England, School of Environmental Sciences and Natural Resources

Management, Armidale, New South Wales 2351, Australia.Bloem, J., Wageningen University and Research Centre, Alterra Green World Research, PO Box 47,

NL-6700 AA Wageningen, The Netherlands.Bouma, J., Wageningen University and Research Center, Environmental Sciences Group, PO Box 47,

NL-6700 AA Wageningen, The Netherlands.Brussaard, L., Wageningen University and Research Centre, Sub-department of Soil Quality,

PO Box 8006, NL-6700 EC Wageningen, The Netherlands.Burgess, L.W., University of Sydney, School of Land, Water and Crop Sciences, New South Wales

2006, Australia.Carter, M.R., Agriculture and Agri-Food Canada, Crops and Livestock Research Centre, 440

University Avenue, Charlottetown, Prince Edward Island C1A 4N6, Canada.Christensen, B.T., Danish Institute of Agricultural Sciences, Department of Agroecology, PO Box 50,

DK-8830 Tjele, Denmark.Condron, L.M., Soil, Plant & Ecological Sciences Division, PO Box 84, Lincoln University,

Canterbury 8150, New Zealand.Dick, W.A., The Ohio State University, School of Natural Resources, 1680 Madison Avenue, Wooster,

Ohio 44691, USA.Didden, W.A.M., Wageningen University and Research Centre, Sub-department of Soil Quality,

PO Box 8006, NL-6700 EC Wageningen, The Netherlands.Donovan, N.J., New South Wales Agriculture, Elizabeth Macarthur Agricultural Institute,

Private Mail Bag 8, Camden, New South Wales 2570, Australia.Drinkwater, L.E., Cornell University, Department of Horticulture, Plant Science Building, Ithaca,

New York 14853, USA.Edel-Hermann, V., CMSE-INRA, U.M.R. Biochimie, Biologie Cellulaire et Ecologie des Interactions

Plantes Microorganismes, F 21065 Dijon, France.Elmholt, S., Danish Institute of Agricultural Sciences, Department of Agroecology, PO Box 50,

DK-8830 Tjele, Denmark.Eriksen, J., Danish Institute of Agricultural Sciences, Department of Agroecology, PO Box 50,

DK-8830 Tjele, Denmark.

v



de Goede, R.G.M., Wageningen University and Research Centre, Sub-department of Soil Quality,PO Box 8006, NL-6700 EC Wageningen, The Netherlands.

Goossens, D., Catholic University of Leuven, Laboratory for Experimental Geomorphology,Redingenstraat 16, B-3000 Leuven, Belgium.

Govers, G., Catholic University of Leuven, Laboratory for Experimental Geomorphology,Redingenstraat 16, B-3000 Leuven, Belgium.

Gregorich, E.G., Agriculture and Agri-Food Canada, Central Experimental Farm, Ottawa K1A 0C6,Canada.

Johnston, A.E., Rothamsted Research, Harpenden, Herts AL5 2JQ, UK.Karlen, D.L., USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, Iowa 50011,

USA.Kay, B.D., University of Guelph, Department of Land Resource Science, Guelph, Ontario N1G 2W1,

Canada.Kuyper, T.W., Wageningen University and Research Centre, Sub-department of Soil Quality,

PO Box 8006, NL-6700 EC Wageningen, The Netherlands.Lal, R., The Ohio State University, Carbon Management and Sequestration Center, Columbus,

Ohio 43210, USA.Locke, M.A., USDA-ARS, Southern Weed Science Research Unit, PO Box 350, Stoneville,

Mississippi 38776, USA. Present address: National Sedimentation Laboratory, Water Qualityand Ecological Processes Research Unit, PO Box 1157, Oxford, Mississippi 38455, USA.

Megharaj, M., University of South Australia, Centre for Environmental Risk Assessment andRemediation, Mawson Lakes Boulevard, Mawson Lakes, South Australia 5095, Australia.

Munkholm, L.J., Danish Institute of Agricultural Sciences, Department of Agroecology, PO Box 50,DK-8830 Tjele, Denmark.

Naidu, R., University of South Australia, Centre for Environmental Risk Assessment andRemediation, Mawson Lakes Boulevard, Mawson Lakes, South Australia 5095, Australia.

Owens, G., University of South Australia, Centre for Environmental Risk Assessment andRemediation, Mawson Lakes Boulevard, Mawson Lakes, South Australia 5095, Australia.

Poesen, J., Catholic University of Leuven, Laboratory for Experimental Geomorphology,Redingenstraat 16, B-3000 Leuven, Belgium.

Schjnning, P., Danish Institute of Agricultural Sciences, Department of Agroecology, PO Box 50,DK-8830 Tjele, Denmark.

Steinberg, C., CMSE-INRA, U.M.R. Biochimie, Biologie Cellulaire et Ecologie des InteractionsPlantes Microorganismes, F 21065 Dijon, France.

Van den Akker, J.J.H., Wageningen University and Research Centre, Alterra Green World Research,PO Box 47, NL-6700 AA Wageningen, The Netherlands.

Wienhold, B.J., USDA-ARS, Soil and Water Conservation Research Unit, University of Nebraska,East Campus, Lincoln, Nebraska 68583, USA.

Zablotowicz, R.M., USDA-ARS, Southern Weed Science Research Unit, PO Box 350, Stoneville,Mississippi 38776, USA.

vi Contributors



Preface

Soil quality is how well soil does what we want it to do. The statement, extracted from the websiteof the USDA Soil Quality Institute, represents the very essence of the soil quality concept.At first glance, one might be tempted to leave the subject, overwhelmed by the enormouscomplexity embedded in this statement. Alternatively, one might analyse the two aspectsof soil quality separately: how well relates to grading soils, while what we want relates topriority of soil functions. Most previous books on soil quality have emphasized the descriptivegrading of soils or management effects, often by focusing on soil-quality indicators. In theeditorial group, however, we were more concerned with soil quality as it relates to whatwe want the soil to do. Clearly, we must define what we want before we can consider howwell this service is delivered. What glues the two aspects together is soil management. Ourambition was therefore to switch from a more passive attitude to a more active and manage-ment oriented attitude. The readers will judge how successful we have been, but if this bookcan promote a revitalized discussion on the soil quality conceptual framework, we certainlyconsider our effort worthwhile.

Science is a human activity, and science and society interact. The focus of sciencewill inevitably reflect the priorities of society. In societies with a shortage of food supply, thefocus will be on soil productivity, while in developed countries with an abundant supply ofaffordable food, the focus will switch from sheer productivity to the overall sustainability of thefood production activities. Sustainable agriculture involves a sustained productivity but alsothe protection of natural resources. The concept of soil quality is deeply rooted in considerationson sustainable production, but since the priorities of society change over time and differ fromone society to another, soil quality cannot be aligned with the universal laws of nature. Theconcept of soil quality is a human construct allowing specific soil functions to be evaluatedagainst specific purposes.

In this book, we have identified a number of specific challenges in modern agriculture.All contributors were encouraged to identify the thresholds in terms of management, whichare necessary to secure soil quality. This does not mean that soil-quality indicators are notdiscussed, but the focus of this book is on management and the identification of research needsand implementation of existing knowledge. Although most contributions are concerned withchallenges facing industrialized countries, the book also includes a chapter considering soilquality in developing countries.

The editorial work was financially supported by the Danish Ministry of Food, Agricultureand Fisheries and based on a decision by the Parliament to create an overview of the influenceof modern agriculture on soil quality. We wish to thank the Danish Institute of AgriculturalSciences for hosting the project. Thanks to Jesper Waagepetersen, Head of The Department of

vii



Agroecology, who chaired the project executive committee, and to committee members forfruitful suggestions during the initial phases of the work.

The book links to the efforts of the European Society for Soil Conservation (ESSC). In 1998,the ESSC decided to accentuate a number of soil protection issues and the senior editor wasappointed to lead a task force on the soil quality concept. This was a main incentive to give thepresent work a truly international perspective. We sincerely hope that the book will serveto facilitate communication among scientists and between scientists and decision makers insociety. Although still developing, the soil quality concept may be useful in the creation ofcodes of conduct by governments and inter-governmental organizations.

We wish to thank all contributors to the book and we most gratefully acknowledge theirefforts. Although busy with numerous other serious commitments, these distinguished expertstook the time to prepare high quality manuscripts. Thanks also to all anonymous referees forreviewing the contributions.

We thank Dr Hugo Fjelsted Alre at the Danish Research Center for Organic Farming(DARCOF) for fruitful discussions on the role of values in science. We acknowledge the verypositive and constructive cooperation with Tim Hardwick and colleagues at CABI Publishing.Last but not least, we thank Ms Anne Sehested for carrying out the tedious work of bringing thecontributions into full accordance with the requests of the publisher. Part of the editorial workwas linked to ongoing projects financed by DARCOF (ROMAPAC, PREMYTOX and NIMAB).

Per Schjnning, Susanne Elmholt, Bent T. ChristensenResearch Centre Foulum

March 2003

viii Preface



Chapter 1Soil Quality Management

Concepts and Terms

P. Schjnning, S. Elmholt and B.T. ChristensenDanish Institute of Agricultural Sciences, Department of Agroecology,

PO Box 50, DK-8830 Tjele, Denmark

Summary 1Agricultural Research in a Changing World 2Science and Society the Need for Reflexive Objectivity 3The Soil Quality Concept 4Sustainability 5Stability in Terms of Resistance and Resilience 6Soil-quality Indicators 8Indicator Threshold and Management Threshold 9Challenges in Modern Agriculture 9Outlining the Book Content 11References 12

Summary

The industrialization of agriculture and the concurrent increase in societal concerns on environmentalprotection and food quality have put the focus on agricultural management and its impact on soil quality.Soil quality involves the ability of the soil to maintain an appropriate productivity, while simultaneouslyreducing the effect on the environment and contributing to human health. This development has changedsocietys expectations of science and there is an urgent need to improve the communication amongresearchers from different scientific disciplines. The interaction of scientists with decision makers is a topicof utmost relevance for future developments in agriculture. Reflexive objectivity denotes the exercise ofraising ones consciousness of the cognitive context, i.e. societal priorities, and the values and goals of theresearcher. The term sustainability comprehends the priorities in the cognitive context and thus constitutesa valuable tool for expressing the basis of scientific work. Soil quality evaluations should include aware-ness of the stability of any given quality attribute to disturbance and stress. This implies addressing resis-tance and resilience of the soil functions and/or the physical form in question. Most existing literature onsoil quality focuses on assessment of soil quality rather than the management tools available to influencesoil quality. Identification of management thresholds rather than soil-quality indicator thresholds is suggestedas an important means of implementing the soil quality concept. The major challenges facing modernagriculture include proper nutrient cycling, maintained functions and diversity of soil, protection of anappropriate physical form and avoidance of chemical contamination. It is suggested that these challengesand problems as related to the soil quality concept are discussed in the framework expounded above.

CAB International 2004. Managing Soil Quality: Challenges in Modern Agriculture(eds P. Schjnning, S. Elmholt and B.T. Christensen) 1

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Agricultural Research in aChanging World

The foundation of modern agriculture waslaid more than 150 years ago. At that time anawareness of the role of plant nutrientsin crop production emerged, supported byexperiments showing the beneficial effectsof adding mineral fertilizers to the soil.However, the most rapid development hasoccurred since the early 1950s. This develop-ment has been driven not only by scientificachievements, but also by access to affordableenergy, traction power and other techno-logical achievements that reduced the timeand manpower required for agricultural pro-duction. Mineral fertilizers, pesticides andcultivars that respond effectively to increasednutrient levels were important requisitesin the dramatic increase in productivity. Thedevelopment of modern agriculture was sup-ported by government policies introducingsystems of production and commodity subsi-dies with the overall aim to secure adequateand reliable sources of food of good qualityand at affordable prices. The side effects werestructural changes towards larger and morespecialized production units and a massivemovement of labour force from agriculture tothe industry and service sectors. Governmentpolicies also involved a substantial increasein the research supporting agriculturalproduction.

In the developed and industrializedcountries, modern agriculture achieved theseprimary goals, and even more so, as demon-strated by surplus production and subsidizedexport of agricultural products. This hascontributed to a switch in societal concernsfrom sheer productivity to sustainability ofagriculture, including the effects of produc-tion methods on the environment, the diver-sity of the natural flora and fauna, the welfareof domestic animals, and the soil resourceitself. The quality of air, water and as yet to aminor extent soil has come more into focus.

Almost every aspect of modern agri-culture is now under scrutiny from concernedproducers, environmentalists and consumers,from researchers and government as wellas non-governmental organizations, and

agricultural sustainability is on the agendaof most political movements and parties.Concerns, attitudes and opinions about agri-cultural production are effectively communi-cated and amplified by news media. At thesame time, the number of economic subsidiesdevoted to agriculture is being questioned.The demands for economic and ecologicalsustainability are bound to introduce changesin the production concepts of modern agri-culture. This development has increased thedemand for scientifically based solutions thatincorporate a wider range of aspects. Scien-tists have been involved in problem solvingand development in society for centuries, butthe pressure from society for a proactive roleof science is much greater than previously.

Another aspect is the increased inter-action between descriptive and prescriptivebranches of science (Ellert et al., 1997).Typically, scientists in ecology, geographyand other classical scientific disciplinesperceive soil as an ecosystem component,and their approach is descriptive and observa-tional in nature. Agricultural researchers, onthe other hand, are concerned primarily withthe production of food and fibre, and perceivesoils mainly as media to support plant growth.Fertility trials, crop rotation studies, tillageexperiments, etc. have provided the basis foran increasing productivity. Thus, researchersinvolved in agricultural sciences are accus-tomed to producing prescriptions with theclear aim of increasing yields. Ellert et al.(1997) advocated a combination of the concep-tual/ descriptive approaches of ecologists andthe quantitative/prescriptive approaches ofagronomists.

However, the vast amount of scientificliterature concerned with ecosystem health,sustainable farming, soil fertility and soilquality reveals problems in communication.As an example, Doran et al. (1996) reportedon communication failures due to differentopinions on the use of values in science. In thesection below we discuss some basic issuesregarding the role of science in society, whichwe believe may facilitate communication. Thephilosophical deductions should be regardedas a laymans view, not as a professionalcontribution to the theory of science.

2 P. Schjnning et al.



Science and Society the Need forReflexive Objectivity

Agricultural research is an applied sciencewith the main objective of improving pro-duction methods and developing productionsystems. In consequence, agricultural scienceinfluences its own subject area, agriculture,in important ways (Lockeretz and Anderson,1993). In general, science that influences itsown subject area is defined as systemic science(Alre and Kristensen, 2002). This character-istic is also true for health, environmental andengineering sciences. The fact that scienceplays a proactive role in the world that itstudies makes the criterion of objectivity as ageneral scientific ideal less straightforward.The general understanding of objectivityis derived from the positivistic criterion ofverifiability of knowledge. Freeman andSkolimowski (1974) defined object as thetotality of external phenomena constitutingthe not-self and hence objective as some-thing that is external to the mind. Thatis, objectivity is defined as opposite to thesubjective. However, when the subject (thescientist in systemic sciences) is part ofthe object (the system studied), an extradimension is added to his/her role as ascientist. It is, therefore, important that thescientist is able to view her- or himself as partof the system (self-reflection). As an example,the researcher involved in the optimization ofcrop yields by management strategies shouldbe able to recognize the consequences of his/her prescriptions on other aspects than justyield. This ability to take an objective stancebut at the same time being aware of theintentional and value-laden aspects of scienceis denoted reflexive objectivity, and the frame-work in which these reflections take placeis labelled the cognitive context (Alre andKristensen, 2002). The cognitive contextmay be divided into three dimensions: theobservational, the societal and the intentional(Fig. 1.1). The observational context includesthe actual methodological aspects of theresearch, the societal context is the group orsegment for which the research is relevant,and the intentional context is the goals andvalues employed.

The observational context comprises thecharacteristics of a scientific work, which areevaluated by the procedure of peer review(such as the experimental set-up, statisticaltreatment of data and discussion of resultsin relation to other relevant studies). Theselection of research topics and the choice ofmethods will frame the outcome of the work(Dumanski et al., 1998), and the methodo-logical aspects of a work are more importantto the results and conclusions than oftenrealized. For example, a study of phosphorusavailability in soil might reach quite differentconclusions depending on the analyticalmethod. Extraction by sulphuric acid wouldyield much more P than a resin (anionexchange membrane based) methodology.Obviously, you would say. The point is,however, that when judging the results, oneuses present-day knowledge of the labilityof different P-pools in soil. There may wellbe plantsoil interactions of importance forP-uptake by plants that we have yet to realize.And such knowledge might induce newmethodologies. Our cognition regarding Pavailability in soil is thus highly dependenton how we establish our analyses.

Concepts and Terms 3

Fig. 1.1. The three dimensions of the cognitivecontext in science. Cognition (perception) isdependent on observational aspects (experimentalset-up), societal priorities, and intentions and goalsfor the scientist or scientific group performing thescientific studies. Please consult the text for details.Based on Alre and Kristensen (2002).



The relevance of the scientific workdepends on the societal context pervading atthe time of the study. There is no universalscience that is independent of social context.When pesticides became available to farmersin the mid 20th century, the most relevant taskfor agricultural researchers was to optimizetheir use for maximum production andminimum costs. When on the other hand an agricultural scientist is engaged in thedevelopment of organic farming, completelydifferent topics dominate. The paradigmassociated with organic farming gives priorityto quality aspects of crops, soil and theenvironment. Concerning pesticides, todaysscientists in industrialized countries areengaged in studies of the detrimental ratherthan the beneficial effects of pesticides (e.g.groundwater pollution, bioaccumulation,side effects on non-target organisms). Theseexamples serve to illustrate that the societalcontext has changed dramatically during theperiod discussed here.

The intentional context in science isperhaps the most controversial. It has to dowith values and goals for the specific researchgroup or scientist. Sojka and Upchurch (1999)gave a critical review on the concept ofsoil quality. Some of their concerns wereabstracted as we are . . . reluctant to endorseredefining the soil science paradigm awayfrom the value-neutral tradition of edaphol-ogy and specific problem solving to aparadigm based on variable, and often sub-jective societal perceptions of environmentalholism. That is, the authors support the classi-cal understanding of objectivity in science. Intheir paper, however, they draw attention toarticles dealing with different aspects of soilquality and raise the query of whether a highbiodiversity in soil is more valuable thananimals at the other end of the food chain.We interpret their statement as giving a highproduction of foods (for higher animals) ahigher priority than a high biodiversity in thesoil. This is of course a legitimate standpoint,but the point is that this opinion also reflectsan intention or a value/goal. Awareness ofthese values is what reflexive objectivity isall about. And the example clearly illustratesthat reflexive objectivity in the room of thecognitive context would facilitate or even be a

prerequisite for communication. We concurwith the statement by Jamieson (1992) andEllert et al. (1997) that frank discussions aboutthe values involved in concepts like soilquality may be equally or more importantthan the technical development and use ofindicators to manage ecosystems.

Scientific work cannot be fully under-stood when detached from the societal andintentional contexts. Campbell et al. (1995)stated that the classification of sustainabilityand health of an agroecosystem require theestablishment of specific judgement criteria,and concluded that such judgement criteriamust be established from a viewpoint that isecologically, politically, socially and economi-cally acceptable. As stated by Munasingheand Shearer (1995) there is bound to be conflictamong such interests. The task of scientistsis thus to provide information that enablesdecision makers to choose among conflictingobjectives by assessing the trade-offs amongthese objectives and the consequences of theirapplication.

The Soil Quality Concept

The term quality implies value judgement(degree of excellence). Thus soil quality isconcerned with some measure of a propertyor function of soil (good/bad, low/high,etc.). Fundamentally, classification of dataand information about soil seems to be a basichuman need, and the concept of soil capabil-ity (good or bad for a specific purpose) isas old as civilization itself (Carter et al., 1997).Patzel et al. (2000) stated that soil qualityencompasses an indefinite (open) set oftangible or dispositional attributes of thesoil. Thus the concept of soil quality may beregarded as a vessel for various attributes ofinterest in any given situation. As an exam-ple, soil quality in the context of highwayconstructions is concerned with the bearingcapacity of the soil medium but does notconsider soil functions for plant growth.Although some people may regard this open(indefinite) concept as truly academic and oflittle use, we think it facilitates reflections onthe value-laden character of the soil qualityconcept. Any decision on quality attributes




enclosed by the concept of soil quality willnecessarily be based on viewpoints, valuesand goals from the societal and intentionalcontexts.

Blum and Santelises (1994) and Blum(1998) considered the functions and servicesof soil as related to human activity andgrouped them into six categories. Three eco-logical uses are: (i) the production of biomass;(ii) the use of soils for filtering, buffering andtransforming actions; and (iii) the provision ofa gene reserve for plant and animal organ-isms. Three other functions relate to non-agricultural human activities; (iv) a physicalmedium for technical and industrial struc-tures; (v) a source of raw materials (gravel,minerals, etc.); and (vi) a cultural heritage.This classification of human interest inand interaction with soil may facilitate anoperational definition of soil quality.

Several definitions of soil quality havebeen advanced (see Karlen et al., Chapter 2,this volume). Most definitions relate soilfunctions to: (i) biological productivity; (ii) theenvironment; and (iii) different expressionsof plant, animal and/or human health (e.g.Doran and Parkin, 1994; Doran et al., 1996).A committee appointed by the Soil ScienceSociety of America (SSSA) offered thefollowing definition (Fig. 1.2): Soil quality is thecapacity of a specific kind of soil to function, withinnatural or managed ecosystem boundaries, tosustain plant and animal productivity, maintain or

enhance water and air quality, and support humanhealth and habitation (Allan et al., 1995; Karlenet al., 1997). Although this definition creates aframework for considering soil quality, it doesnot eliminate the value-laden character ofthe concept. To determine soil quality, thefunctions or services expected of the systemmust be defined and delineated (Ellert et al.,1997). Judgement of what is good or badis influenced by subjective and/or societal pri-orities and decisions. Accordingly, Pankhurstet al. (1997) noted that most authors contri-buting to their book on biological indicatorsof soil health emphasized the holistic natureof the soil health concept and acceptedsubjective assessments of what is healthy. Thesame holds for the soil quality concept.

Early papers on soil quality emphasizedterms like fitness for use in regard to agri-cultural use of soil (Larson and Pierce, 1991,1994). Letey et al. (2003) preferred the termuse to function because use highlights themanagement aspect of the term. However, afunction like carbon sequestration in soil andits interaction with greenhouse gases occursirrespective of agricultural use; only the mag-nitude of this soil function can be manipulatedby agricultural management.

As opposed to other definitions of soilquality, the SSSA definition mentions humansonly in the health part of the text. Concernsregarding plants and animals are associatedwith the productivity part. We find this note-worthy because the expression promotion ofplant and animal health (Doran and Parkin,1994; Doran et al., 1996) in its extended inter-pretation is very ambitious (animals includenematodes and collembola, for example). Weagree that the activity and the diversity of thesoil community are important, and that a largebiomass and a high biodiversity in soil maylink to the degree of soil quality. However,our attitude emphasizes that agriculture bydefinition is a human activity designed for theproduction of food and fibres.

Sustainability

The term sustainability is frequently usedin scientific papers dealing with agriculturalsystems and is closely linked to societal and


Fig. 1.2. Soil quality with its three concerns:biological productivity, the environment and humanhealth. Based on Allan et al. (1995).



individual priorities. The term may beregarded as a manifestation of priorities,values and goals of researchers and society.A link between soil quality and sustainabilityis important because soil quality shouldnot remain an abstract concept but rathersomething to be strived for by management(Bouma et al., 1998).

Sustainability entered public debatefollowing the work of the World Commissionon Environment and Development, labelledthe Brundtland Report (WCED, 1987). Tosustain means to keep up, maintain (OxfordAdvanced Learners Dictionary of CurrentEnglish, 1974). If applied only in this sense,sustainability does not make much sensefor the constantly changing human society.Originally, sustainability more accuratelytranslates into sustainable development (Bossel,1999). Accordingly, the concept of sustainabledevelopment was proposed by the Brundt-land Commission as economic developmentthat meets the needs of the present generationwithout compromising the ability of futuregenerations to meet their own needs (WCED,1987).

When applying the concept of sustain-ability to agriculture, a somewhat more tangi-ble definition has to be constructed, althoughSwift (1994) noted that the concept wouldstill be complex. It would embody issuesof economic viability, the quality of life andhuman welfare, and ecological stability andresilience over time. Several other papersand documents have discussed the issue ofsustainability in greater depth, all emphasiz-ing the combination of biophysical and socialaspects of the concept (e.g. Stewart et al., 1991;Smyth and Dumanski, 1993; Lal, 1994, 1998;Herdt and Steiner, 1995; Munasinghe andShearer, 1995).

Smyth and Dumanski (1993) stated that

Sustainable land management combinestechnologies, policies and activities aimed atintegrating socio-economic principles withenvironmental concerns so as to simulta-neously: (i) maintain or enhance productionand services; (ii) reduce the level of produc-tion risk; (iii) protect the potential of naturalresources and prevent degradation of soiland water quality; (iv) be economicallyviable; and (v) socially acceptable.

Bouma et al. (1998) underscored the fivecriteria for sustainability in this definition,i.e. productivity, security, protection, viabilityand acceptability, and suggested that thesecriteria should also be used for judging soilquality. We have adopted this suggestion forframing the soil quality discussion in thisbook. We further endorse the viewpoint ofStewart et al. (1991) and Pankhurst (1994) thatsustainability should be considered dynamicbecause, ultimately, it will reflect the changingneeds of an increasing global population.

Stability in Terms of Resistanceand Resilience

Evaluation of systems requires estimatesof their stability when stressed or disturbed.Stability may express: (i) the resistance tochange in function or form during a stressevent, or (ii) the capacity to recover functionaland structural integrity (resilience) after adisturbance. It is important to distinguishbetween resistance and resilience. In popu-lation ecology, resistance is defined as thecapacity to resist displacement from anequilibrium condition, whereas resilience isdefined as the capacity of a population (orsystem) to return to an equilibrium followingdisplacement in response to a perturbation(Swift, 1994). We tend to follow Seybold et al.(1999) by using the term resistance instead ofstability, which occasionally has been used toexpress the capacity of resisting disturbance(e.g. Kay, 1990). We find that stability is moreappropriate as a common denominator forresistance and resilience.

Eswaran (1994) emphasized that soil res-ilience relates to either performance or stateor structure of the system. The same appliesto resistance. According to Eswaran, perfor-mance refers to functions and processes inthe soil while state or structure refers to thepedological composition of the material. Thelatter is analogous to the structural form (Kay,1990), although Eswaran had a larger timespan in mind than Kay. Thus, resilience relatesto the ability of recovering functions as wellas to physical form. Figure 1.3 illustrates therelationship between the terms discussed.




A soil may exhibit a high resistance but apoor resilience with respect to some specificproperty. This would be the case if subjectinga dry clay soil to heavy mechanical loads. Thesoil strength and thus its resistance to compac-tion is high. If, however, the structural formcollapses, which would happen at a very highload, it would probably be associated witha compaction along the virgin compressionline (Larson et al., 1980). And the resilience the ability to recover from such compactioneffects is poor (e.g. Hkansson and Reeder,1994). Alternatively, a soil may exhibit a poorresistance but a high resilience for someattribute. A number of microbial soil functionsshow examples of this when subjected to,for example, pesticide applications. Pesticidesmay cause response deficits of more than 90%and yet the soil function may return to its orig-inal level so quickly that the ecotoxicologicaleffect can be regarded as insignificant whencompared to natural stress effects (Domschet al., 1983).

Although the stability of soil systemsshould be assessed both in terms of resistanceand resilience, the latter property particularlydeserves attention when evaluating soilquality in managed ecosystems. As any formof agriculture disturbs the original equilib-rium of the native ecosystem, it is evident thatresilience is a key parameter when judging

the sustainability of agricultural systems. Theconcept of resilience was originally coined byHolling (1973) with emphasis on the persis-tence of relationships within a system. Resilientsystems may show the capacity to occupymore than one state of equilibrium (Swift,1994). Each state of equilibrium may maintaina qualitative structural and functional integ-rity but the quantitative properties may differamong equilibria. This dimension of theresilience concept is crucial when dealingwith managed ecosystems. Any form ofagricultural activity disturbs the originalequilibrium of the native ecosystem, and soilresilience can be invoked to connote the abilityof management to maintain the performanceof the soil (Eswaran, 1994). This interpretationmay be controversial, but is logical when deal-ing with managed ecosystems. Managementis an integrated part of the agroecosystem, andresilience should be related to equilibria inthe managed system, not the performance orstate that would prevail in the original, nativeecosystem (Blum, 1998).

Resilience has been defined from variouspoints of view for various purposes (Szabolcs,1994). One important aspect is the timescale. The rate of soil formation from theparent rock is extremely low compared withthe potential rate of soil loss in unsustainableagricultural systems (Lal, 1994; Pennock,1997). Lal (1994) reviewed the estimates ofrates of soil formation for a number of soiltypes and concluded that most soils can beconsidered a non-renewable resource withinthe human life span. However, a soil subjectedto severe gully erosion may be judged resilientalso to this disturbance if regarded in thecontext of geological time spans of hundredsor thousands of years. Thus, the time factorhas to be considered when discussing soilresilience.

It should be emphasized that the expres-sion of resilience has no meaning withoutan explicit statement of the agents, forces oreffects (disturbance) facing the soil (Szabolcs,1994). Blum (1998) discussed the potentialdisturbances and classified the correspond-ing type of resilience into three groups:(i) resilience to physical disturbances; (ii)chemical resilience; and (iii) resilience tobiological disturbances.


Fig. 1.3. Soil stability in terms of resistance andresilience as related to the suggested term formcomprising soil functions as well as structural form.A stable form may be due to a high resistanceand/or a high resilience. The arrow indicates thata given stability is assigned to a given form, butalso that the stability may change with a change in(pheno)form. Based on Kay (1990) and Droogersand Bouma (1997).

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Soil-quality Indicators

Soil quality assessment typically includesthe quantification of indicators of soil quality.Such indicators may be derived fromreductionistic studies, i.e. specific soil para-meters obtained from different disciplinesof soil science (e.g. Larson and Pierce, 1991).However, descriptive indicators, which areinherently qualitative, can also be used inassessing soil quality (Seybold et al., 1998;Munkholm, 2000). Soil-quality indicatorscondense an enormous complexity in thesoil. They are measurable surrogates forprocesses or end points such as plant pro-ductivity, soil pollution and soil degradation(Pankhurst et al., 1997). Herdt and Steiner(1995) and Carter et al. (1997) drew attentionto situations where individual indicatorsshow opposite or different trends. Larsonand Pierce (1994) and later Doran and Parkin(1996) realized the weaknesses in expressingsoil quality information in single numbers,at least in comparative studies of soilmanagement. As stated by Doran and Parkin,such indicators may provide little infor-mation about the processes creating themeasured condition or performance factorsassociated with respective managementsystems. Thus, the interpretation of soil-quality indicators requires the experienceand skill of the researcher and/or soilmanager. Doran (2002) realized that severalsoil-quality indicators would be too complexto be used by land managers or policymakers. Hence, he suggested concentratingon simple indicators, which have meaningto farmers. The use of indicators like topsoildepth and soil protective cover in a givenmanagement system were hypothesized tobe the most fruitful means of linking sciencewith practice in assessing the sustainabilityof management practices (Doran, 2002).Schjnning et al. (2000) showed that quantita-tive soil mechanical properties derived byanalytical procedures in the laboratorycorrelated well with qualitative behaviourof soil in the field. It seems important toevaluate such links when consideringthe use of soil-quality indicators obtainedby reductionistic studies in controlledenvironments.

Larson and Pierce (1991) suggested aminimum data set to describe the quality of asoil. This data set should consist of a numberof indicators describing the quality/healthof the soil. Using an analogue to humanmedicine, reference values for each indicatorwould set the limit for a healthy soil (Larsonand Pierce, 1991). The use of indicators hasbeen widely discussed in the literature on soilquality (e.g. Doran and Jones, 1996). Lilburneet al. (2002) and Sparling and Schipper (2002)presented achievements obtained in a NewZealand soil quality project. In contrast tomost other soil quality assessments, theirfocus was on a regional rather than on afarmor field scale.Managementwas similarlyaddressed in terms of distinct land uses (e.g.arable cropping, dairy farms, pine planta-tions). Much effort was allocated to identifythe most adequate indicators, and seven keyparameters were chosen: soil pH, total C andN,mineralizable N, Olsen P, bulk density andmacroporosity (Sparling and Schipper, 2002).Lilburne et al. (2002) identified the difficulttask of isolating the relevant target/thresholdvalues of indicators. Sparling and Schipper(2002) acknowledged the problem in address-ing satisfactorily all combinations of soiltypes and land uses. Generally, however, theyfound the approach useful to raise an aware-ness of soil quality issues among regionalcouncil staff, scientists and thegeneralpublic.

We agree that indicators per se as well astheir thresholds may be important in orderto make the soil quality concept operational.The authors of the individual chapters ofthis book have been encouraged to identifyindicators and thresholds whenever it waspossible to establish generally applicable lim-its. However, we realized that this endeavourwould be difficult due to the vast number ofsoil types and agroecosystems addressed. Thehuman species is well defined comparedwithsoils and a body temperature of 37C is anestablished threshold for a healthy person, atleast regarding infectious diseases. Seyboldet al. (1998) and Sojka and Upchurch (1999)stressed the difficulty in dealing with the18,00020,000 soil series occurring in theUSA.Considering the diverse agricultural uses ofsoils (e.g. growing different crops with dis-similar soil requirements) and the different


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optima associated with each specific use,Sojka and Upchurch (1999) emphasized under-standing rather than rating of the soil resource.However, within a well-defined scenario, forexample research in agricultural managementat one specific site or region, the quantificationof soil attributes and the use of these asindicators of soil quality may be quite useful(e.g. Campbell et al., 1997).

Indicator Threshold andManagement Threshold

Threshold was defined by Smyth andDumanski (1993) as levels beyond which asystem undergoes significant change; pointsat which stimuli provoke response. Thusthreshold links to resilience. As an example,Smyth and Dumanski mentioned the thresh-old for erosion as the level (extent of erosion)beyond which erosion is no longer tolerable(in order to maintain sustainability). Gomezet al. (1996) adopted this definition and usedthe term threshold to denote the boundarybetween sustainable and unsustainableindicator values. Thus, thresholds are valuesof a variable beyond which rapid, often expo-nential, negative changes occur (Pieri et al.,1995). Because of their intimate associationwith resilience, we encourage that focus is onthresholds rather than on references, baselines orbenchmarks, often employed in the literatureon soil-quality indicators.

A main issue when considering thequality of agricultural soil is how to identifysustainable management. One major aim ofthis book is to promote a shift from assessingsoil quality to managing soil quality. Of coursemanagement cannot be addressed withoutevaluating soil attributes (i.e. indicators), butby focusing on the effects of management weintended to establish a more relevant founda-tion for the soil quality concept. Our ambitionwas to concentrate on the challenges facingagriculture in the context of maintaining soilquality. When the common knowledge on soilfunctions and properties (including indicatorthresholds) is combined with that derivedfrom studies on the effects of specific manage-ment tools, the potential outcome can be

management thresholds, i.e. the most severe dis-turbance any management may accomplishwithout inducing significant changes towardsunsustainable conditions. Regarding soilacidity, soil pH is a soil-quality indicator forwhich a threshold can be established, whereasthe rate of liming (e.g. kg CaCO3/ha/year)required to maintain the pH at some pre-scribed level represents the managementthreshold.

The management threshold approach mayseem less ambitious than the indicator thresholdapproach, which includes the identificationof a universal minimum dataset. However,the former may be more successful in solvingkey management problems in agriculture.Exerting all efforts in coping with the problemof non-universality in indicator thresholdsimplies the risk of never approaching themanagement problems. The managementapproach, however, also needs to considerdifferences among soil types and agro-ecosystems, and should be based on athorough understanding of the reaction ofindividual soils to management. Figure 1.4illustrates the differences in the twoapproaches discussed.

Challenges in Modern Agriculture

Modern agriculture faces a number of chal-lenges, which are subject to intense research,but they are seldom defined and discussed inthe context of all three aspects of the soil qual-ity concept (Fig. 1.2). As an example, farmersare challenged to manage plant nutrients inorder to maintain production volumes, mini-mize losses of nutrients to the environmentand create a high quality in plant products foranimal and human consumption.

When addressing the challenges ofmodern agriculture, a main issue is theidentification of management procedures thatare sustainable, that is, simultaneously meetsocietal concerns and recognize the vulner-ability of the soil system to degradation. Theauthors of all chapters have been encouragedto explain their judgement of sustainability.Ideally, management options are consideredin relation to the three concerns of the SSSA




definition of soil quality (Fig. 1.2); that is, howwill different soil management affect bio-logical productivity, the environment framingthe managed soil system and human health.The latter relates primarily to the quality ofproducts for human consumption. We havefurther asked for a consideration of soil stabil-ity to a given management practice, applyingthe concept suggested above (Fig. 1.3). Thisimplies identifying resistance as well asresilience of the soil to the influence fromthe specific management applied. Finally, agoal-directed approach includes discussionand, if possible, identification of soil indicatorthresholds as well as management thresholds forthe soil characteristics and the management

procedures discussed in each chapter(Fig. 1.4).

Figure 1.5 summarizes the approach usedin this book for discussing soil managementas related to soil quality. In the centre standsthe major challenges and management tools,which will be discussed in relation to: (i) thethree aspects of soil quality; (ii) the stability ofform (physical form or soil functions); and(iii) the potential of identifying soil-qualityindicator thresholds as well as managementthresholds. Figure 1.5 also illustrates howthese considerations are framed by theunderstanding of sustainability and furtherby societal priorities, and the values and goalsof the scientist (the cognitive context).


Fig. 1.4. Schematic illustration of the indicator threshold approach typically applied in soil qualitystudies (top) and the management threshold approach suggested for this volume (bottom). In the indicatorthreshold approach, the focus is on identifying (universal) thresholds for specific soil-quality indicators,whereas for the management threshold approach, the focus will be put on identifying thresholds (probablynon-universal) for specific management tools.



Outlining the Book Content

One major concern in agriculture is anadequate supply of nutrients to the crops.Chapters 3, 4, 5 and 6 of this volume addressaspects crucial to basic soil processes andplant nutrition. Soil acidity influences mostsoil functions. Nitrogen, phosphorus andpotassium are three important macro-nutrients, i.e. nutrients taken up by cropsin amounts of kilograms per hectare. Moregeneral aspects of the soil ecosystem aretopics of Chapters 7, 8 and 9, which deal withsoil diversity, including carbon dynamicsand biodiversity. The physical form of soilsis treated in Chapters 10, 11 and 12,with emphasis on physical degradation of

agricultural soils. Chemical contaminants aremajor threats to soil quality. Chapters 13 and14 evaluate the potential hazards from theuse of organic waste materials and pesticides.

The contributions addressing specificmanagement problems are framed by fourconceptual chapters. Chapter 2 reviewsthe history of and advances in soil qualityresearch. Chapter 15 is an important reminderthat systems research may reveal mechanismsnot perceived in analytical research. Finally,any work on soil quality should reflect on howthe knowledge gained can be implemented.Hence, Chapters 16 and 17 discuss how to putsoil quality knowledge to work for industrial-ized and developing countries, respectively.Figure 1.6 gives an outline of the book content.


Fig. 1.5. Illustration of the approach used in focusing major challenges in modern agriculture as related toscientifically based terms and as framed by societal values and priorities. Note that only the societal andintentional dimensions of the cognitive context (cf. Fig. 1.1) are active in defining sustainability.



References

Allan, D.L., Adriano, D.C., Bezdicek, D.F., Cline,R.G., Coleman, D.C., Doran, J.W., Haberen, J.,Harris, R.G., Juo, A.S.R., Mausbach, M.J.,Peterson, G.A., Schuman, G.E., Singer, M.J. andKarlen, D.L. (1995) SSSA statement on soilquality. In: Agronomy News, June 1995, ASA,Madison, Wisconsin, p.7.

Alre, H.F. and Kristensen, E.S. (2002) Towards asystemic research methodology in agriculture.Rethinking the role of values in science.Agriculture and Human Values 19, 323.

Blum, W.E.H. (1998) Basic concepts: degradation,resilience, and rehabilitation. In: Lal, R., Blum,W.E.H., Valentine, C. and Stewart, B.A. (eds)

Methods for Assessment of Soil Degradation. CRCPress, Boca Raton, Florida, pp. 116.

Blum, W.E.H. and Santelises, A.A. (1994) A conceptof sustainability and resilience based on soilfunctions: the role of ISSS in promotingsustainable land use. In: Greenland, D.J. andSzabolcs, I. (eds) Soil Resilience and SustainableLand Use. CAB International, Wallingford, UK,pp. 535542.

Bossel, H. (1999) Indicators for Sustainable Develop-ment: Theory, Method, Applications. A Report tothe Balaton Group. International Institute forSustainable Development, Manitoba, Canada,124 pp.

Bouma, J., Finke, P.A., Hoosbeek, M.R. andBreeuwsma, A. (1998) Soil and water quality


Fig. 1.6. An outline of the book chapters indicating the four groups of challenges addressed in specificchapters.



at different scales: concepts, challenges,conclusions and recommendations. NutrientCycling in Agroecosystems 50, 511.

Campbell, C.A., Janzen, H.H. and Juma, N.G. (1997)Case-studies of soil quality in the Canadianprairies: long-term field experiments. In:Gregorich, E.G. and Carter, M.R. (eds) SoilQuality for Crop Production and EcosystemHealth. Developments in Soil Science 25,Elsevier, Amsterdam, pp. 351397.

Campbell, C.L., Heck, W.W., Neher, D.A., Munster,M.J. and Hoag, D.L. (1995) Biophysicalmeasurement of the sustainability oftemperate agriculture. In: Munasinghe, M.and Shearer, W. (eds) Defining andMeasuring Sustainability. The BiogeophysicalFoundations. The World Bank, Washington,DC, pp. 251273.

Carter, M.R., Gregorich, E.G., Anderson, D.W.,Doran, J.W., Janzen, H.H. and Pierce, F.J. (1997)Concepts of soil quality and their significance.In: Gregorich, E.G. and Carter, M.R. (eds) SoilQuality for Crop Production and EcosystemHealth. Developments in Soil Science 25,Elsevier, Amsterdam, pp. 119.

Domsch, K.H., Jagnow, G. and Anderson, T.H.(1983)An ecological concept for the assessmentof side-effects of agrochemicals on soilmicroorganisms. Residue Reviews 86, 65105.

Doran, J.W. (2002) Soil health and global sustain-ability: translating science into practice.Agriculture, Ecosystems and Environment 88,119127.

Doran, J.W. and Jones, A.J. (eds) (1996) Methods forAssessing Soil Quality. Soil Science Societyof America Special Publication Number 49,410 pp.

Doran, J.W. and Parkin, T.B. (1994) Definingand assessing soil quality. In: Doran, J.W.,Coleman, D.C., Bezdicek, D.F. and Stewart,B.A. (eds) Defining Soil Quality for a SustainableEnvironment. Soil Science Society of AmericaSpecial Publication Number 35, pp. 321.

Doran, J.W. and Parkin, T.B. (1996) Quantitativeindicators of soil quality: a minimum data set.In: Doran, J.W. and Jones, A.J. (eds) Methodsfor Assessing Soil Quality. Soil Science Societyof America Special Publication Number 49,pp. 2537.

Doran, J.W., Sarrantonio, M. and Liebig, M.A. (1996)Soil health and sustainability. In: Sparks, D.L.(ed.) Advances in Agronomy. Academic Press,San Diego, California, pp. 154.

Droogers, P. and Bouma, J. (1997) Soil survey inputin explanatory modeling of sustainable soilmanagement practices. Soil Science Society ofAmerica Journal 61, 17041710.

Dumanski, J., Pettapiece, W.W. and McGregor, R.J.(1998) Relevance of scale dependentapproaches for integrating biophysical andsocio-economic information and developmentof agroecological indicators. Nutrient Cycling inAgroecosystems 50, 1322.

Ellert, B.H., Clapperton, M.J. and Anderson, D.W.(1997) An ecosystem perspective of soil qual-ity. In: Gregorich, E.G. and Carter, M.R. (eds)Soil Quality for Crop Production and EcosystemHealth. Developments in Soil Science 25,Elsevier, Amsterdam, pp. 115141.

Eswaran, H. (1994) Soil resilience and sustainableland management in the context of AGENDA21. In: Greenland, D.J. and Szabolcs, I. (eds)Soil Resilience and Sustainable Land Use. CABInternational, Wallingford, UK, pp. 2132.

Freeman, E. and Skolimowski, H. (1974) The searchfor objectivity in Peirce and Popper. In:Schilpp, P.A. (ed.) The Philosophy of Karl R.Popper. The Open Court Publishing Co.,La Salle, Illinois, pp. 464519.

Gomez, A.A., Kelly, D.E.S., Syers, J.K. andCoughlan, K.J. (1996) Measuring sustainabilityof agricultural systems at the farm level. In:Doran, J.W. and Jones, A.J. (eds) Methods forAssessing Soil Quality. Soil Science Societyof America Special Publication Number 49,pp. 401409.

Herdt, R.W. and Steiner, R.A. (1995) Agriculturalsustainability: concepts and conundrums.In: Barnett, V., Payne, R. and Steiner, R. (eds)Agricultural Sustainability: Economic, Environ-mental and Statistical Considerations. John Wiley& Sons, Chichester, UK, pp. 113.

Holling, C.S. (1973) Resilience and stability ofecological systems. Annual Review of Ecologyand Systematics 4, 123.

Hkansson, I. and Reeder, R.C. (1994) Subsoilcompaction by vehicles with high axle load extent, persistence and crop response. Soil andTillage Research 29, 277304.

Jamieson, D. (1992) Ethics, public policy, and globalwarming. Science Technology & Human Values17, 139153.

Karlen, D.L., Mausbach, M.J., Doran, J.W., Cline,R.G., Harris, R.F. and Schuman, G.E. (1997) Soilquality: a concept, definition, and frameworkfor evaluation. Soil Science Society of AmericaJournal 61, 410.

Kay, B.D. (1990) Rates of change of soil structureunder different cropping systems. Advances inSoil Science 12, 152.

Lal, R. (1994) Sustainable land use systems and soilresilience. In: Greenland, D.J. and Szabolcs, I.(eds) Soil Resilience and Sustainable Land Use.CABInternational,Wallingford,UK,pp.4167.




Lal, R. (1998) Soil quality and agriculturalsustainability. In: Lal, R. (ed.) Soil Quality andAgricultural Sustainability. Ann Arbor Press,Chelsea, Michigan, pp. 312.

Larson, W.E. and Pierce, F.J. (1991) Conservationand enhancement of soil quality. In: Evaluationfor Sustainable Land Management in theDeveloping World. International Board forSoil Research and Management, Bangkok,Thailand, pp. 175203.

Larson, W.E. and Pierce, F.J. (1994) The dynamicsof soil quality as a measure of sustainablemanagement. In: Doran, J.W., Coleman, D.C.,Bezdicek, D.F. and Stewart, B.A. (eds)Defining Soil Quality for a SustainableEnvironment. Soil Science Society of AmericaSpecial Publication Number 35, pp. 3751.

Larson, W.E., Gupta, S.C. and Useche, R.A. (1980)Compression of agricultural soils from eightsoil orders. Soil Science Society of America Journal44, 450457.

Letey, J., Sojka, R.E., Upchurch, D.R., Cassel, D.K.,Olson, K., Payne, B., Petrie, S., Price, G.,Reginato, R.J., Scott, H.D., Smethurst, P. andTriplett, G. (2003) Deficiencies in the soilquality concept and its application. Journalof Soil and Water Conservation 58, 180187.

Lilburne, L.R., Hewitt, A.E., Sparling, G.P. andSelvarajah, N. (2002) Soil quality in NewZealand: policy and the science response.Journal of Environmental Quality 31, 17681773.

Lockeretz, W. and Anderson, M.D. (1993) Agri-cultural Research Alternatives. University ofNebraska Press, Lincoln, Nebraska, 239 pp.

Munasinghe, M. and Shearer, W. (1995) An intro-duction to the definition and measurement ofbiogeophysical sustainability. In: Munasinghe,M. and Shearer, W. (eds) Defining andMeasuring Sustainability. The BiogeophysicalFoundations. The World Bank, Washington,DC, pp. xviixxxii.

Munkholm, L.J. (2000) The Spade Analysis aModification of the Qualitative Spade Diagnosisfor Scientific Use. DIAS report, Plant ProductionNo. 28. The Danish Institute of AgriculturalSciences, Tjele, Denmark, 73 pp.

Oxford Advanced Learners Dictionary of CurrentEnglish (1974) Oxford University Press,Oxford.

Pankhurst, C.E. (1994) Biological indicators ofsoil health and sustainable productivity.In: Greenland, D.J. and Szabolcs, I. (eds)Soil Resilience and Sustainable Land Use. CABInternational, Wallingford, UK, pp. 331351.

Pankhurst, C.E., Doube, B.M. and Gupta, V.V.S.R.(1997) Biological indicators of soil health:synthesis. In: Pankhurst, C.E., Doube, B.M. and

Gupta, V.V.S.R. (eds) Biological Indicators of SoilHealth. CAB International, Wallingford, UK,pp. 419435.

Patzel, N., Sticher, H. and Karlen, D.L. (2000) Soilfertility phenomenon and concept. Journal ofPlant Nutrition and Soil Science 163, 129142.

Pennock, D.J. (1997) Effects of soil redistribution onsoil quality: pedon, landscape, and regionalscales. In: Gregorich, E.G. and Carter, M.R.(eds) Soil Quality for Crop Production andEcosystem Health. Developments in Soil Science25, Elsevier, Amsterdam, pp. 167185.

Pieri, C., Dumanski, J., Hamblin, A. and Young, A.(1995) Land Quality Indicators. World BankDiscussion Papers 315, The World Bank,Washington, DC, 63 pp.

Schjnning, P., Munkholm, L.J., Debosz, K. andElmholt, S. (2000) Multi-level assessment ofsoil quality linking reductionist and holisticmethodologies. In: Elmholt, S., Stenberg, B.,Grnlund, A. and Nuutinen, V. (eds) SoilStresses, Quality and Care. Proceedings from NJFSeminar 310, 1012 April 2000, s, Norway.DIAS report 38, Danish Institute of AgriculturalSciences, Tjele, Denmark, pp. 4352.

Seybold, C.A., Mausbach, M.J., Karlen, D.J. andRogers, H.H. (1998) Quantification of soilquality. In: Lal, R., Kimble, J.M., Follett, R.F.and Stewart, B.A. (eds) Advances in SoilScience. CRC Press, Boca Raton, Florida,pp. 387404.

Seybold, C.A., Herrick, J.E. and Brejda, J.J. (1999)Soilresilience: a fundamental component of soilquality. Soil Science 164, 224234.

Smyth, A.J. and Dumanski, J. (1993) FESLM: an Inter-national Framework for Evaluating SustainableLand Management. World Resources Reports73, Land and Water Development Division,FAO, Rome, 77 pp.

Sojka, R.E. and Upchurch, D.R. (1999) Reservationsregarding the soil quality concept. Soil ScienceSociety of America Journal 63, 10391054.

Sparling, G.P. and Schipper, L.A. (2002) Soil qualityat a national scale in New Zealand. Journal ofEnvironmental Quality 31, 18481857.

Stewart, B.A., Lal, R. and El-Swaify, S.A. (1991)Sustaining the resource base of an expandingworld agriculture. In: Lal, R. and Pierce, F.J.(eds) Soil Management for Sustainability. Soiland Water Conservation Society, Ankeny,Iowa, pp. 125144.

Swift, M.J. (1994) Maintaining the biological statusof soil: a key to sustainable land management?In: Greenland, D.J. and Szabolcs, I. (eds)Soil Resilience and Sustainable Land Use.CAB International, Wallingford, UK,pp. 235247.




Szabolcs, I. (1994) The concept of soil resilience.In: Greenland, D.J. and Szabolcs, I. (eds) SoilResilience and Sustainable Land Use. CABInternational, Wallingford, UK, pp. 3339.

WCED (1987) Our Common Future: the BrundtlandReport. Report from the World Commissionon Environment and Development (WCED).Oxford University Press, Oxford.




Chapter 2Soil Quality, Fertility and Health Historical

Context, Status and Perspectives

D.L. Karlen,1 S.S. Andrews2 and B.J. Wienhold31USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, Iowa 50011,USA; 2USDA- NRCS, Soil Quality Institute, 2150 Pammel Drive, Ames, Iowa 50011,

USA; 3USDA-ARS, Soil and Water Conservation Research Unit, University ofNebraska, East Campus, Lincoln, Nebraska 68583, USA

Summary 17Evolution of the Soil Quality Concept 18

Introduction 18Defining soil quality 19Assessment tools and indicator selection 20Inherent and dynamic soil-quality indicators 21Implementation of the soil quality concept 21

Relationships among Soil Fertility, Health, Productivity and Management 23Soil fertility and soil quality 24Soil services, soil health and soil quality 24Soil productivity and soil quality 25Soil management effects on soil quality 25Soil quality management strategies 26

Interpreting Soil Quality Data 26Perspectives for Using the Soil Quality Concept 30References 31

Summary

Evolution of the soil quality concept and its relationship to soil fertility and health are discussed. Aframework for evaluating soil quality is also presented. Soil quality assessment begins by selecting themanagement goal(s) (e.g. productivity, waste management, carbon sequestration) for which the evaluationis being made. Critical soil functions (e.g. nutrient cycling, water infiltration and retention, filtering andbuffering) associated with each goal are identified. Finally, appropriate physical (e.g. aggregate stability,bulk density), chemical (e.g. pH, organic carbon, total N, EC, phosphorus) and biological (e.g. potentiallymineralizable N, microbial biomass, soil enzymes) indicators are selected to measure how well eachfunction is being performed. Scoring algorithms help to interpret the indicator data, with each having soil-and site-specific threshold and optimum values to accommodate differences in soil properties, climate ormanagement practices (e.g. tillage, fertilization, crop rotation or water management). The framework can

CAB International 2004. Managing Soil Quality: Challenges in Modern Agriculture(eds P. Schjnning, S. Elmholt and B.T. Christensen) 17



be modified to evaluate construction sites, athletic fields, forests or other land uses by selecting differentcritical functions, indicators and scoring algorithms. We conclude by stressing that soil quality is not anend in itself but rather a science-based soil management tool for modern agriculture and other land uses.

Evolution of the Soil Quality Concept

Introduction

Alexander (1971) suggested developingsoil quality criteria in reference to agri-cultures role in environmental improvement.Warkentin and Fletcher (1977) subsequentlyintroduced the soil quality concept per se atan international seminar on soil environmentand fertility management for intensive agri-culture. They stressed that the concept wasneeded to facilitate better land-use planningbecause of the increasing number of functions(e.g. food and fibre production, recreation,and recycling or assimilation of wastes orother by-products) that soil resources musteither provide or accommodate.

During its evolution, the soil qualityconcept has been examined using severalapproaches. These range from simple score-card and test-kit monitoring for educationalpurposes to comprehensive laboratory-basedassessments and indexing as a tool to evaluatethe sustainability of various soil managementpractices (Larson and Pierce, 1991; Doran andParkin, 1994; Doran et al., 1996; Gregorich,1996; Karlen et al., 1997, 2001). None of theapproaches, however, ever implied that thesoil quality concept was expected to replacemodern soil survey programmes or diminishthe importance of technology and scientifi-cally-based soil management. Rather, as theintensity of modern agriculture increases (i.e.profit margins narrow, land and other naturalresources become more scarce, world popula-tion increases, and public concern for off-siteimpacts of agriculture grows), the need tounderstand soil quality not as an end in itselfbut as a science-based tool that can be used tohelp guide soil management decisions willonly increase. It is within this context that thisbook emphasizes soil quality management inrelation to agricultural practices rather thansimply monitoring soil-quality indicators, and

thus appropriately brings the soil quality con-cept full-circle from when it was introduced.

Warkentin and Fletcher (1977) suggestedseveral ways to manage soil quality. One wasto determine the critical soil function(s) withinan ecosystem and then to evaluate howadequately those functions were beingperformed. This approach was suggested forintensive agricultural operations, assumingthe information could be used to improvefuture land-use decisions. A second approachwas to determine the number of feasibleoptions for which a specific soil resourcecould be used. High quality soils would bethose capable of supporting a larger numberof different land uses. Soil quality could alsobe determined based on the absence of pollu-tants, analogous to some water and air qualitydeterminations. For this approach, soil qualitywould be quantified by determining thesuitability of a soil for several different uses.For example, if soil resources were used fordisposal of toxic waste materials and thiscreated irreversible changes that would makethose soils unsuitable for other functions (e.g.crop production, recreation or urban develop-ment), the overall soil quality rating would belower (less desirable) than if applying wastematerials did not impair the resource for otherpotential uses. This consideration of irrevoc-able system changes anticipated the state andtransition models currently being developedfor range management (Friedel, 1991).Warkentin and Fletcher (1977) concluded bystating that a soil quality concept was neededto complement soil science research bymaking our understanding of soils morecomplete and to help guide labour, fiscal andinput allocation as agriculture intensifies andexpands to meet increasing world demands.

As we begin the 21st century, thedemands and expectations for our soilresources continue to increase. Worldwideneed for food, feed and fibre production,recreational areas, reforestation and carbon

18 D.L. Karlen et al.



sequestration, urban development andremediation of wastes are just some of thesustainable land use and development issuesfor which different stakeholder groups haveexpressed concern. Wynen (2002) stated thatdesertification, salinization and waterloggingof soils are clear indications that the modernways of managing soils are not sustainable.She listed other examples including contami-nation of soil, ground and surface waters withnitrate and pesticides; eutrophication ofinland and near-shore waters; and continuingsoil erosion in all parts of the world.

The importance of soil protection wasalso recognized at the Rio Summit in 1992 withthe result being the adoption of conventionson climate change, biological diversityand desertification in some countries. TheEuropean Commission has outlined a strategyto protect soil resources by including athematic strategy on soil protection withinthe 6th Environment Action Programme.Attention is being given to preventingerosion, deterioration, contamination anddesertification of soil resources with emphasison the decline in soil organic matter (OM)and prevention of pollution (COM, 2002).Recommended activities include describingthe multiple functions of soils, identifying themain threats to soil resources and outliningsoil characteristics relevant to policy develop-ment. To meet those needs, we suggest evalu-ating both inherent (intrinsic) and dynamic(use-dependent) soil properties and processesto ensure that the immediate and long-termeffects of modern agriculture are sustainable.

Defining soil quality

Prior to the mid-1980s, controlling soilerosion and minimizing its effect on crop pro-ductivity were major foci for North Americansoil management research. Gradually atten-tion broadened to include sustainable agri-culture, environmental health and preventionof further soil resource degradation. Animportant outcome of this expansion was theCanadian Soil Quality Evaluation Program(SQEP) and its assessment of soil health(Acton and Gregorich, 1995).

During this same period, Larson andPierce (1991) defined soil quality as the capac-ity of soils to function within the ecosystemboundaries and to interact positively with theenvironment external to that ecosystem. Theywere among the first to propose a quantitativeformula for assessing soil quality and relatingthe changes to soil management practices.As a result, soil quality was recognized andinterpreted as a more sensitive and dynamicway to measure soil condition, responseto management changes and resilience tostresses imposed by natural forces or humanuses. The emerging soil quality conceptalso provided the focus for an InternationalWorkshop entitled Assessment and Monitor-ing of Soil Quality at the Rodale InstituteResearch Center in Emmaus, Pennsylvania.One outcome was agreement that the soilquality concept should not be limited tosoil productivity, but should encompassenvironmental quality, human and animalhealth, and food safety and quality.

Soil quality became more prevalent in thevocabulary of policy makers, natural resourceconservationists, scientists and farmers afterthe US National Academy of Sciencespublished the book Soil and Water Quality:an Agenda for Agriculture (National ResearchCouncil, 1993) and specifically identified theneed for more holistic soil quality research.The increasing interest in the concept resultedin several symposia and publications.Each, however, seemed to provide its owndefinition, list of critical soil functions andapplications for which soil quality should beassessed.

Some equated soil quality with soilfertility and in response, Patzel et al. (2000)attempted to differentiate the two termswithin the German-language literature byextensively examining soil science, agronomicand ethnic studies. They concluded that noneof the existing soil fertility terminology wassynonymous with the soil quality concept andthat both terms were appropriate. Othersconsidered soil quality to be synonymouswith soil productivity (Sojka and Upchurch,1999), an effort that was prematurely institu-tionalized, and a diversion of resources fromefforts aimed directly at developing improvedsoil management practices (Sojka et al., 2003).

Soil Quality, Fertility and Health 19



Linkages between soil productivity andsoil quality are logical because productivity isa critical function for agricultural sustain-ability. Productivity can be reduced throughwind or water erosion, nutrient mining,salinization, acidification, waterlogging orcompaction, all of which are conditionsreflecting reduced soil quality. Furthermore,the effects of soil management on productivitycan be assessed using soil quality attributes.We acknowledge the partial overlap, butargue that the soil quality concept is evenmore encompassing than soil productivitybecause of its emphasis on environmentalexternalities, chemical, physical, and bio-logical properties, multiple land uses andhuman health.

In 1994, Dr Larry Wilding, president ofthe Soil Science Society of America (SSSA)appointed a 14-person committee to define thesoil quality concept, examine its rationale andjustification, and identify the soil and plantattributes that would be useful for describingand evaluating it. The Committee presentedits first report in the June 1995 issue ofAgronomy News, stating that the simplestdefinition for soil quality is the capacity(of soil) to function. An expanded version(Karlen et al., 1997) defined soil quality as thecapacity of a specific kind of soil to function,within natural or managed ecosystem bound-aries, to sustain plant and animal productiv-ity, maintain or enhance water and air quality,and support human health and habitation.This definition was adopted for the presentvolume (Chapter 1).

Assessment tools and indicator selection

Soil quality research and education activitieshave resulted in the development of teachingmaterials, assessment tools and the evalua-tion of many different soil biological, chemi-cal and physical indicators. In the USA, edu-cational materials were developed primarilyin partnership with the NRCS-Soil QualityInstitute (SQI). These include informationsheets, the Soil Biology Primer, Guidelinesfor Soil Quality Assessment in ConservationPlanning and an evolving website with

user-friendly information and a frameworkfor soil quality evaluation. Assessment toolsinclude farmer-based scorecards, soil qualitytest kits and a spreadsheet designed to helpinterpret indicator data and compute soilquality indices.

Patterned after the Wisconsin soil healthcard (Romig et al., 1995), the scorecardsare intended to provide a qualitative self-assessment of a farmers current soil and cropmanagement practices. The visual soil assess-ment (VSA) protocol (Shepherd, 2000) and asoil quality monitoring system (SQMS) (Beareet al., 1999) are two other tools developedto help improve the sustainability of land-management decisions. For all of these visualassessment tools, scoring is relatively simple(e.g. poor, fair, good) and based on generalobservations of tilth, earthworms, runoff,ponding, plant vigour, yield, ease of tillage,soil colour, aroma, structure, cloddiness orsimilar indicators.

Soil quality test kits were developedto provide semiquantitative indicator dataprimarily at the soil surface (07.5-cm depth).Bulk density, infiltration rate, water-holdingcapacity, electrical conductivity, soil pH, soilnitrate and soil respiration were identified as areasonable minimum data set for evaluatingsoil quality at points within a field. Prelimi-nary studies in several locations showed thattest-kit data compared favourably with labor-atory analyses (Liebig et al., 1996). The resultsdemonstrated the potential to use thesetools for screening agricultural soil quality(Sarrantonio et al., 1996) and for evaluatingnon-agricultural soil conditions (e.g. NewYork Citys Central Park; L. Norfleet, NRCS-SQI, Iowa, 2002, personal communication).

For assessments using laboratory data,many different indicators have been evalu-ated to identify those most appropriate formaking assessments at points within a singlefield, across entire fields, farms, watershedsor Major Land Resource Areas. Some (e.g.Larson and Pierce, 1991) have suggested thatidentifying a minimum data set (MDS) couldprovide sensitive, reliable and meaningfulinformation for soil quality assessment. Real-istically a single MDS will probably remainundefined because of the inherent variabilityamong soils, but it may be feasible to identify a

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suite of biological, chemical and physicalindicators that are useful for evaluating site-specific, temporal trends in soil quality. Widevariation in magnitude and importance ofvarious indicators, failure to clearly definesoil quality or soil health, and disagreementamong soil scientists, conservationists andother land managers regarding whichindicators should be measured, as well aswhen and how, are unresolved challenges.

As the soil quality concept continuesto evolve into a tool for modern agriculture,there are several issues associated with indica-tor selection that need to be resolved. Two arespatial and temporal scale (Halvorson et al.,1997; Wander and Drinkwater, 2000). Anotheris the need to demonstrate causal relation-ships between soil quality and ecosystemfunctions (Herrick, 2000). The accuracy, preci-sion and cost of making the MDS measure-ments are also questions that have not beenresolved. However, as people become awarethat soil is a vital and largely non-renewableresource, we anticipate that the use of soilquality assessment will increase. We areconfident that those assessments will helpquantify resistance to degradation (defined asthe capacity of a system to continue function-ing without change when disturbed (Pimm,1984)) and the resilience of a soil resource torecover following disturbance. Ultimately,rules for indicator selection will be created toidentify general trends in soil quality, if notspecific index values. We suggest that animportant role for soil scientists is to helpdetermine those rules so that the assessmentswill be understood by and useful to landmanagers, who are the ultimate stewards ofsoil quality and soil health (Doran and Zeiss,2000).

Inherent and dynamic soil-quality indicators

Inherent soil characteristics are those deter-mined by the soil-forming factors of climate,parent material, time, topography and biota(Jenny, 1941), whereas the dynamic or use-dependent soil properties are those influ-enced by the management practices imposedby humankind. Both are very important with

regard to sustainability. It is also importantto understand that inherent and dynamicindicators are observations in time alonga continuum and that the values will bevariable because soils are living and dynamicsystems. The philosophy that both inherentand dynamic soil properties and processesinfluence soil quality has been discussedpreviously (e.g. Seybold et al., 1998; Karlenet al., 2001) but without reference to thegenoform/phenoform concept of Droogersand Bouma (1997). We suggest that the twoconcepts are closely related.

Evaluating inherent soil properties andinterpreting how they affect land use haveprovided the foundation for soil survey,classification and land-use recommendationsfor more than a century (Kellogg, 1955). Themodern survey has focused on identifyingand grouping soils with similar morphology,properties or functional characteristics andemphasized the suitability or limitations ofeach soil for various uses (e.g. crop produc-tion, recreation, forestry, wetlands, drainagefields, roads or building sites). In contrast,dynamic soil quality assessment has focusedon the surface 2030 cm and attempts todescribe the status or condition of a specificsoil due to relatively recent (i.e. < 210 years)land-use or management decisions. There-fore, traditional soil survey, classificationand interpretation (i.e. inherent soil qualityevaluation) and dynamic soil quality assess-ment are not competing concepts, but comple-mentary. Furthermore, as stated by Herrick(2000), true calibration of soil quality requiresmore than merely comparing values acrosssoils or management systems. Soil qualitymust be viewed in a landscape context sincemost ecosystem functions depend on multipleconnections through time and space.

Implementation of the soil quality concept

Institutional as well as research andeducation activities have contributed to theworldwide evolution and implementationof the soil quality concept. In the USA, thereorganization of the USDA-Soil Conserva-tion Service (SCS) into the Natural Resources

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