Biological approaches to sustainable soil systems - Part 1 pptx

It is in this context that Biological Approaches to Sustainable Soil Systems is an extremely timely and valuable contribution to a wider understanding of what needs to be done for the sa

Global agriculture is now at the crossroads The Green Revolution of the last century thatgave many developing countries such as India a breathing spell, enabling them to adjustthe growth of their human populations better to the supporting capacity of theirecosystems, is now in a state of fatigue Average growth rates in food production as well

as factor productivity in terms of yield per unit of mineral fertilizer (NPK) are bothdeclining Yet, India and other developing nations are still confronted with the need toproduce more food and other farm commodities under conditions of diminishing arableland and irrigation water resources per capita and with expanding biotic and abioticstresses, some linked to global climate changes

In January, 1968, several months before Dr William Gaud coined the term “GreenRevolution,” I made the following statement in a presidential address to the AgriculturalSciences Section of the Indian Science Congress held in Varanasi:

Exploitative agriculture offers great dangers if carried out with only an immediateprofit or production motive The emerging exploitative farming community inIndia should become aware of this Intensive cultivation of land without con-servation of soil fertility and soil structure would lead, ultimately, to the springing

up of deserts Irrigation without arrangements for drainage would result insoils getting alkaline or saline Indiscriminate use of pesticides, fungicides, andherbicides could cause adverse changes in biological balance as well as lead to anincrease in the incidence of cancer and other diseases, through the toxic residuespresent in the grains or other edible parts Unscientific tapping of undergroundwater will lead to the rapid exhaustion of this wonderful capital resource left to

us through ages of natural farming The rapid replacement of numerous locallyadapted varieties with one or two high-yielding strains in large contiguous areaswould result in the spread of serious diseases capable of wiping out entire crops,

as happened prior to the Irish potato famine of 1854 and the Bengal rice famine

in 1942 Therefore, the initiation of exploitative agriculture without a properunderstanding of the various consequences of every one of the changes intro-duced into traditional agriculture, and without first building up a proper scientificand training base to sustain it, may only lead us, in the long run, into an era ofagricultural disaster rather than one of agricultural prosperity

Since enhancement in productivity per unit of land is the only pathway available to mostpopulation-rich, but land-hungry, countries like India, for the purpose of meeting the foodneeds of a fast-growing population, I started working on what I termed “an ever-greenrevolution movement.” Ever-green revolution involves the enhancement of farm produc-tivity in perpetuity without associated ecological or social harm In his 2002 book,The Future of Life, E.O Wilson endorsed this concept:

The problem before us is how to feed billions of new mouths over the next severaldecades and save the rest of life at the same time, without being trapped in a

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Faustian bargain that threatens freedom and security No one knows the exactsolution to this dilemma The benefit must come from an ever-green revolution.The aim of this new thrust is to lift food production well above the level obtained

by the Green Revolution of the 1960s, using technology and regulatory policiesmore advanced and even safer than those now in existence

For an ever-green revolution, we need, first and foremost, to have sustainable soilsystems In spite of all the advances in aquaculture, the soil will remain the mainsource of food It is in this context that Biological Approaches to Sustainable Soil Systems is

an extremely timely and valuable contribution to a wider understanding of what needs

to be done for the sake of a truly modern agriculture and for the sake of futuregenerations We owe a deep debt of gratitude to Dr Norman Uphoff and all the editorsand contributors for their labor of love to the cause of enhancing the productivity andprofitability for a wide range of farming systems on an environmentally sustainable basis

by sharing both scientific knowledge and practical experience

There is a growing conflict between the proponents of organic farming and chemicalfarming Chapters in this book bring out clearly that there is no need to abandon all externalinputs and that there can be synergy between organic and inorganic inputs The bookprovides the scientific basis for low external-input agriculture Soil health is treated in aholistic manner involving attention to the physics, chemistry, and microbiology of soilsystems The various chapters could help scientists chart out and embark on a program

of “soil breeding” for high productivity Such initiatives for sustainable agriculture shouldreceive as much attention as crop breeding has been given if we are to promote advances

in productivity in perpetuity without adverse ecological consequences

Water is becoming a very serious constraint in many countries and of growing concern.This is where Norman Uphoff has rendered a very valuable service by promoting theSystem of Rice Intensification (SRI) method adapted from agronomic practices developed

in Madagascar (Chapter 28) Experience in India has shown that this methodology leads

to nearly 40% saving in water without affecting the yield of the crop, indeed, as a rule,increasing crop yields with reduced external inputs As decisions on land use areinvariably water-use decisions, land and water use will in the future have to be dealtwith in a more integrated manner I hope that this ambitious and timely book will beread and used widely in order to ensure the long-term viability and sufficiency of foodproduction systems around the world

M.S Swaminathan

Norman Uphoff, Andrew S Ball, Erick C.M Fernandes, Hans Herren, Olivier Husson,

Cheryl Palm, Jules Pretty, Nteranya Sanginga and Janice E Thies

Ana Primavesi

3 Soil System Management in Temperate Regions 27

G Philip Robertson and A Stuart Grandy

Richard J Thomas, Hanadi El-Dessougi and Ashraf Tubeileh

5 The Soil Habitat and Soil Ecology 59

Janice E Thies and Julie M Grossman

6 Energy Inputs in Soil Systems 79

Andrew S Ball

Sustainable Soil Systems 91

Volker Ro¨mheld and Gu¨nter Neumann

of Plant – Bacteria Interaction 109

Frank B Dazzo and Youssef G Yanni

Mitiku Habte

Gregor W Yeates and Tony Pattison

11 Soil Fauna Impacts on Soil Physical Properties 163

Elise´e Oue´draogo, Abdoulaye Mando and Lijbert Brussaard

v

12 Biological Nitrogen Fixation in Agroecosystems and in Plant Roots 177

Robert M Boddey, Bruno J.R Alves, Veronica M Reis and Segundo Urquiaga

13 Enhancing Phosphorus Availability in Low-Fertility Soils 191

Benjamin L Turner, Emmanuel Frossard and Astrid Oberson

14 Phytohormones: Microbial Production and Applications 207

Azeem Khalid, Muhammad Arshad and Zahir Ahmad Zahir

Communication 221

Autar K Mattoo and Aref Abdul-Baki

16 Allelopathy and Its Influence in Soil Systems 231

Suzette R Bezuidenhout and Mark Laing

17 Animals as Part of Soil Systems 241

Alice N Pell

to Implementation 257

Bernard Vanlauwe, Joshua J Ramisch and Nteranya Sanginga

in Southern Africa 273

Paramu L Mafongoya, Elias Kuntashula and Gudeta Sileshi

Go¨tz Schroth and Ulrike Krauss

through Agroforestry Practices 305

Erick C.M Fernandes, Elisa Wandelli, Rogerio Perin and Silas Garcia

Learning from Brazilian Experience 323

Lucien Se´guy, Serge Bouzinac and Olivier Husson

Management 343

Olivier Husson, Lucien Se´guy, Roger Michellon and Ste´phane Boulakia

Peter Hobbs, Raj Gupta and Craig Meisner

Michael Mortimore

26 Restoring Soil Fertility in Semi-Arid West Africa: Assessment

of an Indigenous Technology 391

Abdoulaye Mando, Dougbedji Fatondji, Robert Zougmore´, Lijbert Brussaard,

Charles L Bielders and Christopher Martius

Agroecosystems 401

Robert M Boddey, Bruno J.R Alves and Segundo Urquiaga

Robert Randriamiharisoa, Joeli Barison and Norman Uphoff

Erika Styger and Erick C.M Fernandes

Soil Fertility in the Tropics 439

Roland Bunch

Allison L.H Jack and Janice E Thies

Rafael Martinez Viera and Bernardo Dibut Alvarez

Agroecosystems 479

Ramon Rivera and Felix Fernandez

Brendon Neumann and Mark Laing

Biological Inputs 501

O.P Rupela, C.L.L Gowda, S.P Wani and Hameeda Bee

in the Humid Tropics 517

Johannes Lehmann and Marco Rondon

Interventions 531

Astrid Oberson, Else K Bu¨nemann, Dennis K Friesen, Idupulapati M Rao,

Paul C Smithson, Benjamin L Turner and Emmanuel Frossard

Root Health through Deep Tillage 547

Nico Labuschagne and Deon Joubert

Rotation Systems 559

Liu Xuejun, Li Long and Zhang Fusuo

40 Managing Polycropping to Enhance Soil System Productivity:

A Case Study from Africa 575

Zeyaur Khan, Ahmed Hassanali and John Pickett

Alain Ratnadass, Roger Michellon, Richard Randriamanantsoa and Lucien Se´guy

42 Revegetating Inert Soils with the Use of Microbes 603

Gail Papli and Mark Laing

B Selvamukilan, R Rengalakshmi, P Tamizoli and Sudha Nair

46 Measuring and Assessing Soil Biological Properties 655

Janice E Thies

47 Approaches to Monitoring Soil Systems 671

David Wolfe

48 Modeling Possibilities for the Assessment of Soil Systems 683

Andrew S Ball and Diego De la Rosa

Biologically-Based Approaches 693

Norman Uphoff

50 Issues for More Sustainable Soil System Management 715

Norman Uphoff, Andrew S Ball, Erick C.M Fernandes, Hans Herren, Olivier Husson,

Cheryl Palm, Jules Pretty, Nteranya Sanginga and Janice E Thies

This book has been constructed by the editors and contributors as a report on the state

of knowledge and practice for a more biologically oriented and informed agricultureappropriate to a wide range of contemporary agroecosystems It advances numerousexplanations and conclusions for sustainable soil-system management even though weknow this is a rapidly expanding area for research and field-based innovation, with manyanswers still to be found

The editors and contributors, representing many institutions and diverse disciplines,have worked in dozens of countries What has brought them together is their involve-ment with research and/or experience which shows that agricultural production can beincreased at the same time that it is made more sustainable by being less dependent

on the exogenous resources that have driven the expansion of agriculture in the pastcentury The book focuses on and illuminates ways in which endogenous processeswithin soil systems offer opportunities to expand agricultural output with less reliance

on external inputs, even while these continue to play an important role in contemporaryagriculture

The book is neither antichemical in orientation nor opposed in principle to the use

of external inputs These will remain important in the decades ahead, and, in fact, thebook presents much evidence supporting the optimizing use of mineral fertilizers withbiological interventions However, their pre-eminent role will surely change For manyeconomic, environmental, and equity reasons, it would be unwise not to consider alter-native or complementary approaches to conventional “modern” agriculture No one cansay with certainty what will be the future prices and availability of fossil fuel-based energyand agrochemical inputs However, it is unlikely that their costs will not increase in realterms in the years ahead

Fortunately, many opportunities have been emerging in recent years to move culture in more biologically driven directions that are less dependent on such inputs Thisbook shows that there are many ways in which a variety of crops can be produced moreabundantly and more cheaply by managing and intensifying endogenous processes in soilsystems Improvements in the growing environments for crops can capitalize on existinggenetic potential to achieve substantial increases in output, often 50 –100% and sometimesmore, with less reliance on external inputs, as summarized inChapter 49

agri-Many innovations in agricultural systems have been empirical, not driven by scientificknowledge, but rather by efforts to solve specific problems of soil-system constraints

or decline However, it is desirable that technology does not run too much ahead of science.Improvements in soil-system performance should be explicable in terms of scientificknowledge that can make these innovations more generalizable, more transparent, morereplicable, and more optimal and sustainable Knowing better their limitations andfinding additional opportunities can lead to their wider and safer use This book thusseeks to foster a closer connection between science and practice where now there is oftensome estrangement

The 104 contributors come from 28 countries, presently based in Africa (24), the UnitedStates (24), Latin America (18), Asia (18), Western Europe (12), and 4 each in the

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Middle East and Oceania Denominating contributors’ disciplines is difficult since bothoriginal training and current work are important, but these often diverge Becausethe contributors represent so many different disciplines and have divergent roles alongthe research-development continuum, the voices and concerns of the chapters thatfollow present considerable variety The different tones and perspectives that readerswill find in these chapters mirror the diversity of the underground world about whichthe authors are seeking to communicate The variation we trust will make for more inter-esting reading.

We have included both practitioners and researchers in this review since advancingknowledge in this domain is not a simple linear process of going from science to practice.Practice has often given impetus to scientific inquiry and insights We look forward tohaving richer foundations for these various strands of theory and practice in the decadesahead as productive knowledge and experience accumulate However, we can alreadyidentify, assemble, and share enough knowledge so that agriculture in this new centuryappears positioned for a more successful and sustainable future There is no need for dire

or gloomy predictions

Both authors and readers of a book that is intended for a multidisciplinary audienceface a similar challenge — to optimize between breadth and depth The editors invitedpersons with recognized expertise in many different subject areas to contribute from theirknowledge Our request was to focus on the most important things for nonspecialists

to know on the respective subjects without compromising substance and scientific rigor.The editorial team, which collectively has broad and deep expertise on soil systemsaround the world, took responsibility for writing one-third of the book, the remainderbeing by experts from around the world The managing editor, himself a social scientist byoriginal training, undertook to ensure coherence in the full set of presentations and to havethem presented in language that is broadly accessible

As seen from the table of contents, this book represents an effort to chart some newdirections for agricultural science and practice It is not, however, “breaking new ground”

in that what is presented in Parts I and II has roots in the scientific literature that goback often half a century (e.g., phytohormones) or more (e.g., the effects of mycorrhizalassociations)

Much new knowledge is offered through the syntheses and applications presented

in Part III, with amplifications in Part IV Contemporary work shows significant benefitsfrom mobilizing well-documented biological processes within soil systems Agriculturalplants have coevolved with other flora and fauna for several hundred million years Thishas led to many productive symbiotic relationships that are severed when crops aretreated as separate from and independent of the ecosystems in which they function.The original idea for this book was suggested by Russell Dekker, senior editor ofMarcel Dekker, in a discussion in June 2003 with Norman Uphoff, who became managingeditor for this project Both saw value in bringing together what is known from manycountries and disciplines about this “biocentric” way of thinking about agriculturalscience and practice that is gaining ground Special thanks go to Virginia Montopoli atthe Cornell International Institute for Food, Agriculture and Development (CIIFAD) forher support in producing this book An undertaking as ambitious and complex as thisrequired continuous and skilled administrative assistance to bring it to fruition

The concept of an alternative paradigm for crop and soil sciences that is morebiologically oriented came into the literature over a decade ago when one member ofthe editorial team, Pedro Sanchez, presented it in a paper at the 15th World Congress of SoilScience in Mexico (Sanchez, 1994) Since this direction was first articulated, accumulatingknowledge and practice have given shape and momentum to this paradigm

There is still much more to be known and done However, we expect that readerswill agree, after assessing the scientific foundations of this emerging paradigm and itsempirical accomplishments to date, that agriculture in the 21st century can be madeboth more productive and sustainable by accepting this more holistic orientation andassociated knowledge than by simply projecting the current paradigm into the futurewithout considering biological factors and actors in more active and central roles.

Reference

Sanchez, P.A., Tropical soil fertility research: towards the second paradigm In: Transactions of the15th World Congress of Soil Science, Acapulco, Mexico Mexican Soil Science Society, Chapingo,Mexico, 65–88 (1994)

Understanding the Functioning

and Management of Soil Systems

Norman Uphoff, Andrew S Ball, Erick C.M Fernandes, Hans Herren, Olivier Husson, Cheryl Palm, Jules Pretty, Nteranya Sanginga and Janice E Thies

CONTENTS

1.1 Components of Soil Systems 3

1.2 Understanding Soil System Dynamics 5

1.2.1 Difficulties in Analyzing Biological Components 6

1.2.2 Methodological Issues and Opportunities 6

1.3 Soil Systems Analysis and Management 7

1.4 Soil System Interactions 9

1.5 Book Design 10

1.6 Challenges for Agricultural Science and Practice 11

References 12

Soil, the foundation for most terrestrial life, has unrivalled complexity What is seen as mostly mineral and relatively homogeneous material contains uncountable numbers of organisms, as well varying amounts of air and water A single gram of soil usually contains tens to thousands of millions of fungi and bacteria, plus thousands of diverse plant and animal species Indeed, the extraordinary diversity of microbes in the soil remains unappreciated because most, perhaps 95% of them, cannot be cultured and thus have never been examined, classified, or recognized for their ecological significance Terra incognita remains a very relevant concept

Soil scientists have long grappled with the difficulty of discerning the many variations and gradations in soil chemistry and physical structure that have major implications for soil fertility Yet this fertility is a function also of gases, liquids, organic matter, and myriad organisms that are found along with inert solid mineral material This book is about soil systems, rather than about soil, to emphasize the contributions that living components make to something that is variously cultivated, grazed, built on, walked on, and utilized

in other ways It explores the implications of a biologically framed understanding of soil systems for making their management more productive and sustainable

1.1 Components of Soil Systems

Soil systems have four major categories of material content The first is by far the largest in terms of volume, but the last and smallest category has effects on soil system performance that are far out of proportion to its measurable share

3

† Mineral elements are usually about half of the soil’s volume, even though they canappear to be its totality The mineral portion of soil, which differs from system tosystem in its chemical composition and its physical characteristics, has longbeen the focus of most soil science research These mineral elements exist indifferent-sized soil particles, classified (from large to small) as sand, silt, or clay.The mineral composition of soil establishes its physical properties, and itinfluences and is influenced by the life forms that are present.

† Water is usually about a quarter of soil volume, although the actual amount canvary greatly over time and between soil systems With too little water, soil systemsbecome desiccated, and with too much, they are saturated

† Air in well-aggregated soil can be another quarter of the volume, containingoxygen, hydrogen, nitrogen, and carbon in gaseous forms The more pore spacewithin the soil, the greater will be its capacity for holding both water and air whichbenefit plants as well as other flora and fauna in the soil For any given soilporosity, the amounts of water and air are usually inversely related

† Organic material usually comprises only a small portion of soil by volume, usuallybetween 1 and 6%, although it can be higher than this This fourth categoryencompasses (1) nonliving organic matter which is derived from the growth,reproduction, death, and decomposition of plants, animals, and microbes andexists in the soil as humus or as other inanimate material, and (2) an immensevariety of living flora and fauna, referred to collectively as the soil biota Thiscategory includes also (3) plant roots, which actively make soil systems morehospitable for the growth of their shoots and other species The processes involved

in these interactions are addressed inChapter 5andChapter 6

The organic portion of soils includes both soil organisms and the various biologicalsubstances and processes that animate soil systems The connection between the mineraland organic components of soil systems is intimate, converging at the smallest scale

of soil structure and function in what are called clay –humus complexes At the nexthigher level of structure, in microaggregates, inert and living materials are practicallyfused Although this is well known, the biological dimensions of soil systems are toooften regarded more as secondary or intervening variables, rather than as central anddetermining factors

Here and in the chapters that follow, we present a soil-system perspective that is based

on both well-established principles and recent research findings It gives attention tobiological factors without separating them from or opposing them to the soil’s physicaland chemical aspects, because all three sets of factors are and need to remain integrated

We hope a more biocentric perspective will advance the understanding and management

of soil systems so that these can be made more sustainably productive for food productionand for their environmental services

Both above- and belowground biota are the sources of the organic matter that providesnecessary energy stores to soil systems as discussed in Chapter 5 and Chapter 6.Microorganisms decompose and mineralize organic materials and accelerate the weath-ering of inorganic materials that can then be used by plants and other organisms

In addition to solubilizing certain nutrients which then are available for flora and fauna,they also stabilize chemical and physical aspects of the soil, creating a more hospitablehabitat for plants as well as for themselves The activities of all kinds of organismscombine to aggregate the soil, making it possible for water and air to diffuse below thesurface This makes the soil better able to absorb and retain these elements for subsequentuse by plants and other organisms

By breaking down chemical compounds, the soil biota continuously replenish the pool ofnutrients that are available for plants and other biota, at the same time that they utilize many

of these nutrients for themselves This latter process known as “immobilization” makes thenutrients absorbed by microorganisms unavailable, at least at the time, for plants and otherorganisms However, the process could just as well be regarded as a kind of “banking” of soilnutrients, buffering them in the short run and keeping them in the soil for eventual use byplants, rather than being lost through leaching or volatilization Collectively, the biologicalactors in the soil have many and very great consequences for the performance of soil systems.Plants should themselves be understood as active participants in the continuing ebb andflow of soil processes, rather than just as recipients of water and nutrients, of predation bysoil herbivores or infection by pathogens Plant roots continually adjust their interactionswith the soil environment, particularly with the thin layer of biologically rich soil, known

as the rhizosphere that envelops the root system and is modified by root exudation Anexample of how sophisticated this interaction can be is seen in a recent report on maizeplant responses to attacks by the larvae of the western maize rootworm (Diabrotica virgiferavirgifera), a coleopteran pest that feeds on maize roots When the roots of certain maizevarieties are attacked, they emit a chemical signal, the compound (E)-b-caryophyllene,which attracts a nematode Heterorhabditis megiditis which is a natural enemy of therootworm pest to attack the larvae (Rasmann et al., 2005) Similar strategies are operativeabove ground as maize leaves, in response to caterpillar herbivory, emit certain volatilecompounds which attract parasitic wasps to infest the caterpillars (Turlings et al., 1990;Khan et al., 1997; Degenhardt et al., 2000) Such findings indicate that plants are bestunderstood as active rather than as passive participants in soil systems

1.2 Understanding Soil System Dynamics

Soil systems contain complex food webs which exhibit contrasting processes ofcompetition, mutualism, predation, and symbiosis The many and intricate connections

of the food web and how organisms support each other in diverse ways, while in turn beingconsumed by other organisms, are reviewed inChapter 5 Some of these interactions areunusual, and cannot be simply extrapolated from knowledge about aboveground systems.Thus specific scientific knowledge about belowground actors and processes, reviewed inPart II, is important for understanding means to better manage and improve soil systems,presented in Part III

Here are some examples of belowground processes which are very different from thoseobserved above ground

† The fecal pellets (castings) produced by earthworms are populated by microbesthat decompose mineral nutrients in these pellets before they are reingested, thusfunctioning in effect as a kind of “external rumen.” This symbiotic relationshipsupports worms’ capacity to enrich and aerate the soil through which they move

† Symbiotic protozoa that live in the guts of termites break down cellulose thattermites have ingested, thereby enabling their hosts to derive energy from woodwhich no other organisms can digest

† Some species of ants and termites maintain, in effect, “fungus gardens” in theirhills, continuously feeding the resident fungi in order to obtain from them theenergy that enables these “ecosystem engineers” to make the soil more permeable

to air and water

The subterranean world thus contains many unexpected actors and relationships,described in informative detail in recent “underground travelogs” by Wardle (2002) andWolfe (2001) Understanding how this world works requires an integration of chemical,physical, and biological perspectives informed by empirical investigation with a minimum

of preconceptions

1.2.1 Difficulties in Analyzing Biological Components

Studying biological processes and agents is complex, often ambiguous, and invariablymore difficult than assessing chemical and physical factors However, there has been

a burgeoning of research on soil biology and ecology in the last 20 years This bookcould not have been written two decades ago, and even a decade ago it would havecompared poorly with what evidence now available permits us to report

For the sake of simplifying research design and producing replicable results, much soilresearch to date has been carried out under what are called axenic conditions, studyingsoil samples that have been sterilized or fumigated before analysis, thereby eliminatingall living organisms This ensures that no biotic presence or activity will affect the soilbeing evaluated for its physical or chemical properties and relationships (Note thatetymologically the term “a-xenic” means without anything foreign, implying that theorganisms being removed from the soil are alien to it and do not belong there.) Gnotobioticsoil studies are intentionally more biologically oriented, eliminating all but a certainspecies of organism from the soil to study its effects in isolation However, when this isdone, none of the effects of that species’ interactions with other organisms can beconsidered, even though soil biology research has been demonstrating the ubiquity andsignificance of such interactions Having only one species in soil analysis is actually notmuch better than having none, since there can be opposite effects when other organismsare present in the soil, not just larger or smaller effects

For example, research on the soil fungus Trichoderma harzianum has shown thatunder axenic conditions it attacks the mycelium of the beneficial mycorrhizal fungusGlomus intraradices (Rousseau et al., 1996) However, in a soil-based system where otherorganisms are present, researchers have found G intraradices unaffected by the presence of

T harzianum, and in fact, the Trichoderma fungus appears to be suppressed throughnutrient competition (Green et al., 1999, as reported by Whipps (2001)) Thus, notexamining relationships with the whole suite of organisms present and active in the soilcan give misleading results because ex situ studies often give different results from in situinvestigations

Soil research that controls for biological factors by removing them or by making themextraneous to the analysis can produce more apparently precise and replicableexperimental results However, this approach excludes important processes that arepervasively influential under field conditions Conclusions drawn from controlledevaluations are thus only applicable to situations where the same, usually artificialconditions can be found Conclusions based on axenic or gnotobiotic soil samples, whenextrapolated to the real world, should have appropriate qualifications about their limitedapplicability stated clearly and explicitly

1.2.2 Methodological Issues and Opportunities

Soil researchers are confronted with their own version of the uncertainty principle thatWerner Heisenberg proposed for quantum physics, where the act of measurement itselfaffects the phenomena under study Researchers studying living soil relationships have toaccept the fact that they cannot produce as exact or as incontestable results as their peers

who study soil chemistry and soil physics because reductionist methodologies are lessable to illuminate the holistic realm of biology, where emergent properties are particularlyimportant Because of the dynamism of soil systems, the differing results that are oftenobtained when analyzing the same soil at two points in time may be due not tomeasurement error but to variation in the phenomena of interest This discrepancy doesnot represent a failure of measurement, but is more likely a realistic representation ofdiverse and changing soil situations.

Researchers studying soil systems need tolerance for ambiguity, complexity, anduncertainty as they seek to assemble credible and robust explanations of these phenomena.Reductionist methods can and should be used, however, with a sophistication thatappreciates (and talks about) what has been left out of the analysis Sacrificing realismfor the sake of precision and replicability is a trade-off that can lead to more misunder-standing than insight What goes on in soil systems is still incompletely understoodbecause most present scientific knowledge has been based on studies that have under-represented the biological component

Fortunately, in recent years, numerous advances have been made in research methodsfor studying soil biology Good recent examples of such work are found in van Noordwijk

et al (2004), which goes into considerable scientific detail on many of the subjectsaddressed in this volume Indeed, a number of the chapters in this volume report theresults of using some of the most technologically advanced investigation techniques, forexample,Chapter 8on natural Rhizobium-cereal associations,Chapter 15on soil and plantmanagement practices that influence genetic expression for plant senescence andresistance to pests and diseases,Chapter 37on phosphorus availability, and Chapter 40

on polycropping to control weed and insect pests

how they can help us to learn about the functioning of soil systems Chapter 47 and

and practice through monitoring and modeling exercises Many of the means formeasurements now being made of biological actors and activities in soils were notavailable 10 years ago

1.3 Soil Systems Analysis and Management

A growing number of researchers in countries around the world have taken on thechallenge of developing a new and integrated understanding of soil systems, combiningdetailed measurement and reductionist analyses with inclusive understandings of plant,soil, microorganism, climate, and other interactions, and then try to apply this knowledge

to the improvement of agricultural systems The principles governing soil-system tioning have been compared with musical themes by Lucien Se´guy, one of the contributors

func-to this volume Themes in the analysis of soil systems are basically the same acrossdifferent climatic, edaphic, and other conditions, but they will sound somewhat differentwhen played by the different soil-system “orchestras” that differ according to variouscombinations of biophysical and other factors

Well-functioning soil systems have the following requirements according to AnaPrimavesi, another contributor to this volume:

† A well-aggregated soil structure that has sufficient organic matter in the upper soilhorizons so that it can support (1) water and air penetration; (2) aerobic soil life foraggregating the soil and for mobilizing nutrients; and (3) good root development

† Soil protection against the adverse effects of sun and rain (high temperature anderosion) This can be achieved by (1) mulch from crop residues, green manures, orcover crops that keep the surface covered; (2) intercropping or polycropping with

a variety of plants to keep the surface covered; (3) reduced spacing between plants

or planting an undercrop such as groundnut; and/or (4) shading where intensesunshine adversely affects both plants and water

† Diversified and abundant populations of soil organisms to mobilize nutrients

† Extended and well-functioning root systems with widespread access to soilnutrients

† Crops adapted to the soil and climatic conditions, or some adaptation of thegrowing environment to support them, such as provision of nutrients lacking inthe soil

† Windbreaks around cropped areas or reforestation to reduce evapotranspiration,and

† Careful use of machinery to minimize soil compaction, a major hazard for mostsoil systems

Many current standard agricultural practices have negative impacts on soil systems.Plowing not only can contribute to soil erosion; it also disturbs and reduces earthwormand other epigeic fauna populations important for soil fertility By inverting soil layers,plowing kills aerobic organisms on or near the surface by burying them, while eliminatinganaerobic organisms living at lower depths by exposing them to the air The reduced soilporosity that results from compaction creates less favorable conditions for development ofroots and many kinds of microbial life While the application of synthetic fertilizers canhave positive effects, this alters soil chemistry, physics, and biology to different extents.Increasing some but not all of the soil nutrients that are in deficit, and possibly creatingsurpluses of others, can unbalance soil chemistry and biology to the detriment of planthealth and growth The application of some agrochemicals for crop protection also haseffects on populations of soil microflora and fauna, diminishing their biodiversity.Contemporary agriculture has undoubtedly produced many benefits However, thesecan come with substantial economic and ecosystem costs (Waibel et al., 1999; Pretty, 2002;2005; Tegtmeier and Duffy, 2004) Some costs are evident in soil degradation and loss,but often there are greater unseen losses in soil biota Soils with less diverse microbialcommunities have less capacity to suppress pathogenic activity, with resulting plantdiseases The use of agrochemical controls can make disease problems worse in the longterm

Agricultural practices, such as deep plowing and fertilizer application that correct some

of the symptoms of deteriorating soil systems, do not address the causes of thedeterioration and thus do not improve soil conditions in the long run Biologically-basedapproaches aim to promote virtuous rather than vicious cycles, improving conditionsthat will support sustained and beneficial processes The contributions of biologicalunderstanding to soil fertility, discussed in more detail throughout this book, can besummarized as:

† Soil creation Although most soil texts explain this process in terms of physical andchemical processes, biological activity has important roles in soil genesis

† Solubilization and recycling of nutrients Expanding the available pool of nutrients

in the soil is a continuous process, with organisms that operate from micro- tomacroscales contributing more to plant nutrition, even more nitrogen, than

is provided through inorganic amendments (Ladha et al., 1998) The role of plantroots in recycling nutrients is generally undervalued.

† Improvement and stability of soil structure By creating soil aggregates and pores, aswell as mixing minerals and organic matter through the activities of a wide range

of organisms

† Detoxification By decomposing or neutralizing a wide variety of organic andinorganic substances that would otherwise impede the growth of organisms inand above the ground

1.4 Soil System Interactions

Soil systems vary widely in their productivity, their stability, and their resilience, withfactors and processes varying not just between wet and dry or hot and cold seasons, butchanging continuously over time Despite this variation, however, the factors andprocesses involved are reasonably similar across all soil systems, and they commonly varyaround certain fairly predictable states or cycles

Certain processes are faster under tropical conditions than in temperate areas, asdiscussed inChapter 2andChapter 3, but the processes themselves are universal because

of the needs of flora and fauna at different scales The organisms present in soil are neverexactly the same in two different locations, yet the functional categories remain similar.Certain functions are often performed by different sets of flora or fauna, often on an as-needed basis Managing soil systems productively and sustainably requires adaptingcropping principles and practices to particular local conditions, capitalizing on thecomplex systems of interaction that are now coming to be understood better

A schematic representation of soil system dynamics developed from the work of Se´guyand CIRAD researchers in countries including Brazil, Madagascar, France, and Vietnam ispresented inFigure 1.1.This analysis underscores the benefits of maintaining permanentcover on fields as discussed in Chapter 22 to Chapter 24 Various means — biological,chemical, and physical — can be used to control weed competition and alter soil structure,the main reasons for plowing over the millennia Replacing tillage with practices that keepthe soil covered and nurture more biotic activity in the upper horizons is one of manybiologically-based approaches for better management of soil systems This kind of analysisand associated changes in standard agronomic practice are opening up new possibilities,with many other examples considered in Part III These achieve economic productionobjectives in ways that are more compatible with and supported by natural ecosystemprocesses and are also more cost-effective

Soils have often been regarded as a medium for anchoring plants and for receivingfertilizer and other inputs, assuming a fixed endowment of inherent nutrients Anynutrients that are lost through crop production, according to the standard view, must bereplaced whenever exported in order to sustain a given level of fertility Such asimplification of soil processes has supported some demonstrable successes in agronomictheory and practice However, a more multifaceted appreciation of how soils function asdynamic systems can help achieve even greater increases in yield and profitability whilealso contributing to improved soil and water quality

Biologically-based practices with an agroecological perspective do not focus on singlespecies, respectively Instead they address the complex interactions of one or more cropswith soil biota of many kinds, sometimes even incorporating the management of weedsinto cropping systems to take advantage of what such plants can contribute, such as

harboring beneficial insects or putting out more root exudates for the benefit of soilmicrobes The purpose is to create more favorable conditions for desired plant growth,through greater soil porosity, canopy humidity, optimum microclimatic temperatures,nutrient mobilization, and other services Plants have co-evolved over eons with soilorganisms, starting with the services of mycorrhizal fungi some 400 million years ago asascertained from the fossil record (Margulis and Sagan, 1997) Trying to improve theperformance of plants with little or no reference to the environment in which they haveevolved, and with which they have developed systemic interdependence, will surely limitfuture success.

1.5 Book Design

The perspective taken here is not a radical departure from present agriculture, thoughsome proponents of more biologically-oriented approaches may prefer to emphasize thedifferences rather than the similarities We do not see new approaches as displacingpresent ones in a zero-sum way Rather, there is likely to be an accelerated evolution andacceptance of new practices, informed by emerging scientific knowledge and by thesuccess of alternative methods The impetus for this book arose from the substantialimprovements in crop performance that were being achieved through changes in

Erosion controlled by cover/mulch and roots

Soil aeration

C incorporation

Soil structure improved by roots and biological activity

Reduced competition

Weeds controlled

by mulch Shadow effects and allelopathy

Biological pumps Nutrient and water extraction plus recycling by deep and dense root systems

Reduced nutrient losses (and less pollution)

Reduced water and nutrient losses

Increased water reserves

Plant nutrition

Increased nutrients and water availability

Mineralization

of OM Solubilization

of nutrients

N fixation Improvement by fauna Stabilization by mycelium

Increased stability

Increased biological activity

in soil

Preserved habitat Increased humidity

Buffered temperatures Increased OM content

Habitat for micro-organisms Water and air flow Provision of fresh OM

Energy sources Symbiosis

the management of plants, animals, soil, water, and/or nutrients The innovations andevaluations reported inChapters 18,19,21–23,28,29,31,34, 41, and42are ones withwhich members of our editorial group were personally acquainted or involved We wereencouraged also by other work that we were learning about, undertaken by colleaguesfrom around the world and reported in other chapters in Part III and Part IV.

This volume is intended to communicate the scope and substance of biologicalapproaches to managing soil systems (a) to scientists who have an interest in innovationand practice, and (b) to practitioners who are concerned with improving agriculture on abroader scale, both spatially and over time, based on better scientific understandings Part

II presents the major important components and aspects of soil systems from multipledisciplinary perspectives It aims to provide a reasonably inclusive appreciation of what isknown about biological factors in soil systems’ functioning Part III seeks to acquaintreaders with what is being done around the world with the knowledge that isaccumulating for supporting new management approaches It covers accomplishmentsand limitations of current efforts to capitalize on biological potential for improvingagricultural systems Part IV puts these approaches into a more comprehensive setting,addressing important complementary issues and opportunities as well as problems andmethods of measurement, monitoring, and modeling (Chapter 46toChapter 48).Chapter

49assesses the current and prospective context of agricultural development strategies andthen considers what advantages can be achieved with more biologically-drivenapproaches to cropping system improvement.Chapter 50, in conclusion, considers someissues and opportunities related to these new directions for research and development.Before reviewing the constituent elements and processes of soil systems in Part II, theremaining chapters in Part I provide three overviews of soil systems and their management,first in tropical settings (Chapter 2), then in temperate ones (Chapter 3), and further, underarid and semi-arid circumstances (Chapter 4) These discussions provide some integratedperspectives on the challenges that farmers and policymakers face for making better use ofavailable soil resources under the different circumstances for their management

1.6 Challenges for Agricultural Science and Practice

The world in the twenty-first century is going to be quite different from that of the recentpast, as seen from the global data and time-series reviewed inChapter 49 Key trendsinclude the following:

† Arable land per capita by 2050 will be only about one-third of what it was a centuryearlier, projected to be about 0.08 ha per capita, having been 0.24 ha in 1950(Worldwatch Institute data) The world’s farmers will have to increase theirproduction considerably from the available arable land area They cannot afford touse nonsustainable practices to reduce arable area or environmental goods andservices Most agricultural land will need to be utilized more intensively asextensive cultivation practices, inherently less productive, become less feasible

† Production increases will have to be accomplished with diminishing availability

of water per capita More efforts will be needed, for example, to conserve andutilize “green water,” i.e water that is absorbed and stored in the soil and used

in situ (Savenije, 1998) This is different from “blue water,” which is captured inartificial or natural storage facilities or pumped from underground stores and thenconveyed to some point of use Finding ways to induce plants to develop better

plant root systems and building up soil organic matter will be important formaking better use of potential soil water stores.

† Global climate change will adversely affect the productivity of a large part of theworld’s farmland, especially in the tropics and subtropics, where many areas willshift from productive to semi-arid status, while other areas will go from beingsemi-arid to arid Some agricultural areas at higher latitudes may benefit fromgradual warming, but these regions are not where the world’s projected needs forfood production and consumption are greatest Moreover, helping plants developbetter root systems in association with having more effective communities ofsupportive soil biota will be important in the future for enabling crops to copebetter with climatic fluctuations and extreme events

† Ways must be found to reduce the loss of existing soil resources through erosion,salinization, and other forms of land degradation, so that present land shortageswill not become even more serious Already about one-quarter of the world’sarable land can be classified as degraded, and almost one-third of this vulnerablearable area is in Africa and Central America (Brady and Weil, 2002) As far as ispossible, we will need to find ways to restore and improve land previously lostthrough soil-degrading practices

For all these tasks, more knowledge of and reliance on biological processes will be part

of the process of making soil systems more productive and more sustainable, preservingthem and, where they are degraded, rehabilitating them Fortunately, the contributions tothis book provide evidence and reasons to think that these outcomes are attainable We arepleased that the largest number of the innovative management systems reported in Part IIIare from Africa, where more productive and more sustainable agriculture is most needed.Each innovation reported is somewhat different, and where successful it has beenadapted to the agroecosystem into which it was introduced, with a view to capitalizingupon biological potentials not just of the crop (or animal) of interest, but of the wholeassembly of flora, fauna, and microorganisms in that system The production benefits fromsuch approaches are summarized inChapter 49(Table 49.4), to give readers an overview ofthe magnitude and range of agronomic advances already being obtained with suchmethods around the world, under a great variety of climatic, soil, socioeconomic, andother conditions The wider benefits achievable in terms of natural resource conservation,environmental quality, accessibility for capital-limited farmers, and ultimately humanhealth and well-being are much harder to quantify and compare

No final or global assessment is presently possible since sustainability can only bevalidated over many years, and many aspects will probably remain incommensurable.What can be said with some confidence now is that these approaches present greatpotential that is well worth investigating and pursuing How far they spread will depend

on their utility for farmers and their households, and on the net benefits they produce forlarger social and environmental systems

Green, H et al., Suppression of the biocontrol agent Trichoderma harzianum by mycelium of thearbuscular mycorrhizal fungus Glomus intraradices in root-free soil, Appl Environ Microbiol., 65,1428– 1434 (1999).

Ladha, J.K et al., Opportunities for increased nitrogen-use efficiency from improved lowland ricegermplasm, Field Crops Res., 56, 41– 71 (1998)

Margulis, L and Sagan, D., Microcosmos: Four Billion Years of Evolution from Our Microbial Ancestors,University of California Press, Berkeley (1997)

Pretty, J., Agri-Culture: Reconnecting People, Land and Nature, Earthscan, London (2002)

Pretty, J., Ed., The Pesticide Detox, Earthscan, London (2005)

Rasmann, S et al., Recruitment of entomopathogenic nematodes by insect-damaged maize roots,Nature, 434, 732–737 (2005)

Rousseau, A et al., Mycoparasitism of the extramatrical phase of Glomus intraradices by Trichodermaharzianum, Phytopathology, 86, 434–443 (1996)

Savenije, H.H.G., The role of green water in food production in sub-Saharan Africa, Paper preparedfor FAO program on Water Conservation and Use in Agriculture (WCA) (1998), (http://www.wca-infonet.org)

Tegtmeier, E.M and Duffy, M.D., External costs of agricultural production in the United States,Int J Agric Sustainability, 2, 155–175 (2004)

Turlings, T.C., Tumlinson, J.F., and Lewis, W.J., Exploitation of herbivore-induced plant odors byhost-seeking parasitic wasps, Science, 250, 1251– 1253 (1990)

van Noordwijk, M., Cadisch, G., and Ong, C.K., Eds., Below-Ground Interactions in Tropical ecosystems: Concepts and Models with Multiple Plant Components, CAB International, Wallingford,

Soil System Management in the Humid

and Subhumid Tropics

Although tropical soil systems represent an important part of the world’s diversity of soilecosystems, they have in the past received less scientific attention than temperate zonesoils Soil systems in both categories operate according to the same principles, but climaticdifferences have put them on divergent paths Neither should be taken as a norm fromwhich the other deviates In recent years, research on tropical soil systems has been greatlyexpanding, helping us to understand better the general principles according to which soilsystems function

While it is true that agricultural productivity has commonly been greater in temperateregions, differences often arise because tropical soils have frequently been managed withassumptions, practices, and technologies transferred from temperate climatic zones

In fact, tropical soil systems can be very productive when their comparative advantagesare utilized Under natural conditions their gross production of biomass above- and

15

belowground can be multiples of what is produced in temperate climates, in spite ofthe poverty of tropical soils when these are assessed only in terms of available mineralnutrients A tropical Amazonian forest ecosystem, even on poor sandy soil, can produce asmuch biomass in 18 years as will be created under a boreal northern forest on richer soils

in 100 years (Primavesi, 1980)

Even when they are poor in chemical terms, tropical soils can be biologically rich incomparison with the kind of temperate soil systems that are considered in Chapter 3.Whenever soil conditions are warmer and more humid, there will be greater activity ofchemical, physical and particularly biological processes Table 2.1 compares some typicaltraits of tropical Oxisols and Ultisols with those of a Mollisol more characteristic of thefertile plains of Eastern Europe and North America The comparisons indicate somecontrasting differences between typical humid-tropical and temperate soils

Tropical soil systems are located in a broad band around the equator between the Tropic ofCancer and Tropic of Capricorn (231

28lat N and S) They differ from temperate systems mostobviously in terms of their relatively constant temperatures under widely differing moistureregimes Some temperature variations naturally occur due to elevation and rainfall regimes,and neither tropical nor temperate regions are homogeneous Addressing all this variation

in a single chapter is impossible, so the focus here will be mostly on the humid tropics,although the discussion is largely applicable to the subhumid tropics as well.Comprehensive reviews of tropical soils have been provided in Sanchez (1976) andPrimavesi (1980) Significant differences in soil systems and their management arise once theclimatic regimes in tropical areas become arid or semi-arid as reviewed inChapter 4.The tropics with their considerable variation in rainfall (with climates ranging from veryhumid to arid) and vegetation (from dense forest to cleared agricultural lands) encompass

a large part of the earth’s surface All together they are home to about one-third of theworld’s population (Bonell and Hufschmidt, 1993) This region is most noted for itstropical rain forests, but these are diminishing in area under pressures of agriculture,logging, and development

At the equator, day length is always about 12 h, considerably shorter than the longsummer days in temperate regions The latter can have 50 – 100% more daily solar radiationduring their summer growing season, but year-round exposure to intensive sunlight givestropical soil systems more total energy to produce biomass above- and belowground.The other main asset in much of the tropics is moisture, although excess rainfall can become

a liability In the humid equatorial zone where rainfall is most abundant and almostcontinuous, the effects of this resource become dominant Under native vegetation in theAmazon basin, precipitation can exceed 4000 mm year21 This includes localized recycling

TABLE 2.1

Broad Contrasts of Temperate and Tropical Soil System Characteristics

Tropical Oxisol/Utisol Temperate Mollisol

Predominant clay form Variable-charge 1:1 clays,

kaolinites (Si –Al)

Permanent-charge 2:1 clays, montmorillonites (Si –Al–Si) Cation exchange capacities (CEC) Poor (7–150 mmol dm 23 ) Rich (500–2200 mmol dm 23 ) Soil pH Acidic (5.6–5.8 or lower) Neutral (6.8–7.0 or higher) Rooting depth Shallow to very deep Moderate to deep

Key compounds Fulvic acids, leading