The environment and zero tillage

Also,Conservation Agriculture was practiced, for instance with Zero andMinimum Tillage, which leave the crop residues on the soil surface, inorder to increase soil organic matter and red

expanded and updated from

“ O Meio Ambiente e o Pantio Direto”,

1997, by the same editors

Translated byJohn N Landerswith assistance from James P Walker,

Elisa Campos and Helvecio Mattana Saturnino

Brasília/DF2001

E-mail: apdc-df@terra.com.br or apdc@apis.com.br

Federação Brasileira de Plantio Direto na Palha - FEBRAPDP Rua Sete de Setembro, 800 Sala 301-A 3 o Andar

Ponta Grossa - PR

CEP 84010-350

Phone: 55 (42) 223-9107

E-mail: febrapdp@convoy.com.br

Text revised by: James Pinney Walker

Layout and graphics: Formato 9 Produção Gráfica Ltda - Brasília DF Front cover design:??? - adapted from Sirlene Siqueira

Bibliography: ???

Fotolith: ???

Printing: ???

Cover: ‘Crop rotation and good residue generation”

Cover photos: ???, ??? and ???

AUTHORS

Fernando Penteado Cardoso

Manoel Henrique Pereira

Rolf Derpsch

José Roberto Marinho

Garo Batmanian

Osmar Pires Martins

Henrique M Leite Chaves

Alberto Duque Portugal

César Temístocles Hannas

Paulo Afonso Romano

Pedro Luij de Freitas

João Baptista da Silva

Helvécio Mattana Saturnino

ACKNOWLEDGEMENTS

The English edition of this book was inspired and principally funded

by the Food and Agriculture Organisation of the United Nations (FAO).The diversity of the chapter authors implies a certain amount of repetition

of basic principles but this can also be seen as a strength, in that there iswide convergence in their positive opinions on the revolutionary newconcepts of Zero Tillage Without their valuable contributions, this bookwould not have been possible

Partnerships between the public and private sectors are becomingever more necessary, especially in the face of global competition andsustainable development It is in such partnership that one foresees aqualitative leap in Brazil's agriculture, promoting a harmonious interactionbetween man and nature, with technologies which maintain equilibrium

in the exploitation of natural resources The joint efforts ofinternational, Brazilian government and private entities in support of theBrazilian Federation for Zero Tillage in Crop Residues (FEBRAPDP)and the Association for Zero Tillage in the Cerrado Region (APDC)embraces noble objectives in the edition of this book As such, it represents

a key strengthening of a citizens' movement which engenders the exercise

of true democracy, resulting from the mindset change implied in ZeroTillage A significant example of this movement is the founding of theFriends of the Land Clubs which are active in many Brazilianmunicipalities, mobilizing diverse stakeholders interested in thedevelopment and diffusion of this conservation technology, which protectssoil, water and biodiversity

The original (Portuguese) version of this book represented a dedicatedpartnership made possible by the financial and material support from:Agroceres S.A, Embrapa, Fundação Cargill, Manah S/A and the Secretariat

of Water Resources (SRH) of the Ministry of Environment, withoperational support from the Inter-American Institute for Cooperation inAgriculture ( IICA)

The editors

6

Considerations on the Environment :

Message from the President of WWF - José Roberto Marinho

Commentaries of an Ecologist - Garo Batmanian

Comments of the Secretary of Environment for the

Municipality of Goiânia - Osmar Pires Martins

Effects of Zero Tillage on the Environment

Henrique M Leite Chaves

Zero Tillage: Reduction of Environmental Risks with Herbicides

- João Baptista da Silva

C HAPTER VII

ZT and Technology Transfer in the Tropics and Sub-tropics

- Helvecio Mattana Saturnino and John N Landers

C HAPTER VIII

Organizational and Policy considerations in Zero Tillage

- J.N.Landers, H.M.Saturnino and P L de Freitas.

When, in 1995, I had the opportunity to show the Nobel laureateresearch scientist Norman Borlaug what was being achieved in Brazil inreclaiming the infertile, acid soils of the “Cerrado” (Tropical Savannah)and Amazon regions, we sought to show him that we had at our disposaltechnology for sustainable agriculture in the new frontiers of Brazil.

Referring to what he had seen, Dr Borlaug declared in lectures given

in Belo Horizonte and São Paulo:

“It is agronomic management – such as planting at the right time,including Zero Tillage, which I admire because it reduces both erosionand costs – which allows expression of the genetic potential of the newvarieties” (April, 1995)

“In 1995, I had the pleasure to visit various parts of the Cerradoregion I saw many large-scale mechanized operations in which not only

1 June 17 – 21 1996, Goiânia, Goiás State, Brazil, a bi-ennial event, promoted by FEBRAPDP and organised

by APDC in 1996 and 1998.

was liming employed but fertilizers were used to very good effect Also,Conservation Agriculture was practiced, for instance with Zero andMinimum Tillage, which leave the crop residues on the soil surface, inorder to increase soil organic matter and reduce erosion In the centralsavannahs vsited, I saw little erosion” (May 1996)

These conclusions complement the declarations of the speakers atthe 5th Brazilian National Zero Tillage Meeting, where the papers presentedexpressed the authors’ convictions on the subject of Zero Tillage (ZT).This meeting counted with the illustrious presence of Alberto DuquePortugal, President of the Brazilian National Research Corporation –Embrapa; Paulo Affonso Romano, the (National) Secretary of WaterResources of Brazil’s Environment Ministry as well as the representative

of José Roberto Marinho, President of Radio Globo and Chairman of theBoard of Directors of WWF-Brazil and Garo Batmanian, CEO of WWF-Brazil

In the words of the president of Embrapa, we note the auspiciousdevelopment of Zero Tillage, giving credit to those who merit it:

“We researchers started late in this question (ZeroTillage), in which the farmer took the lead I would like tounderline the initiative of the farmers of Central Brazil whopressured research to get involved with Zero Tillage As ameans of improving the identification of research demands,

we have learned that we should pay great attention to whatthe farmer is saying, because he knows what he’s talkingabout”, (see Chapter 4)

With the involvement of the government research institutionsalongside the efforts of the farm input suppliers in divulging thistechnology, both pressured by the farmer in his untiring quest for progress,creative and ever-willing to try new practices, we are progressing surely

in the direction of greater and greater adoption of Zero Tillage The annual

area covered by protective crop residues is growing every year, alreadycovering 4.5 million hectares in 1995/6 and extending to over 14 millionhectares by 1999/20002.

In describing this picture, it is our duty to recognize the apostolates

of three untiring companions in the disseminaion and promotion of ZeroTillage, all motivated by their ideals: Manoel Henrique Pereira and HerbertBartz of Brazilian origin and John N Landers, an Englishman adopted byBrazil They merit recognition from both farmers and technicians, all peers

in the promulgation and stimulation of sustainable agriculture, practicedthroughout the country

Fernando Penteado CardosoAgrolida Ltda., São Paulo-SP, Brasil

2 Figures for the summer-planted maincrop area plus winter small grains.

12

INTRODUCTION

Helvécio Mattana Saturnino

John N Landers

The movement towards sustainable agriculture entails breaking with

a cycle of soil exploitation and poverty that resulted in the degradation

of natural resources, principally those of soil and water (figure 1) Toarrest and even revert this descending spiral represents the objectives

of international agreements, such as Agenda 21 The challenge is exactly

to associate environmental preservation with the actions of povertyalleviation and of economic growth

Figure 1 The Poverty Cycle

Inadequate or exceeding Soil Tillage

Compaction

Direct sunstroke

Lack of coverErosion

net

Around the world it has been recognized that erosion has degraded avaluable patrimony, constituted by the most fertile soils, water resourcesand bio-diversity This has undermined the economic viability of farms,regions and even whole countries The farmer, in most cases coerced bythe existing economic system, does not provide himself with the means toprotect this patrimony and thus de-capitalises himself year after year

Figure 2 Consequences of the erosion of land cultivated under conventional tillage: losses of fertile soil and inputs.

Soil degradation with all its implications and deleteriousconsequences, has resulted in the challenge to develop production systemswhich permit greater energy efficiency and environmental protection,creating new technological paradigms in agriculture, based onsustainability

The search for a fast-growing economy, with less inequality, cannotdispense an ambitious environmental programme which targets the quality

of life Better understanding of the relationships between soil, water andlife quality is imperative in the attainment of balanced and prosperousrural/urban development Many surveys carried out in the world indicatethe need for rationalising the use of soil and water (Figure 3)

Source: FAO - Global Water Resources.

WHAT IS ZERO TILLAGE ?

The experience of Brazilian farmers with Zero Tillage began in theearly 1970’s This was a result of American and British work derivingfrom the advent of the first contact herbicide, Paraquat, which came onthe market at the start of the 1960’s Thus, when the Zero Tillage experiencebegan in Brazil, the United States already were planting over two millionhectares using this technology and its rapid expansion had already beenprojected, adapting the technology to the differing conditions of the USA

This system gained impulse with the discovery of systemic herbicides

(non-selective and selective), guaranteeing greater efficiency in the control

of weeds Better alternatives in planter and seed drill designs and in residueproduction, giving increased soil protection had also been evolving

Figure 4 Planter adapted for Zero Tillage: minimum disturbance of the soil and crop residue cover.

By not discing, ploughing, scarifying and cultivating, or, in otherwords, by not turning the soil over and incorporating organic matter, as isthe case with conventional pre-plant soil preparation, the new system ofZero Tillage (ZT) revolutionised concepts held for thousands of years.This was achieved principally through advances in herbicide researchwhich made it possible to dispense with pre-plant soil preparation InZero Tillage, the process of placing seeds (or seedlings) and/or fertilizer

in the soil, be it manually, with animal traction or by mechanized means,aims at minimum disturbance of soil structure and biological activity,while maintaining the dead mulch cover of residues from prior harvests,

as shown in Figures 4 and 5 But Zero Tillage is not just an alternativeplanting method, it represents a change in agricultural thought patterns toview the whole system, integrating crop rotations and maintenance ofsurface residue with cover crops, integrated management of weeds, pestsand diseases, rational fertilizer practices, watershed management and otherenvironmental concerns This is what confers sustainability on the system

Figure 5 This animal traction planter incorporates the most advanced pneumatic seed distribution technology : it is driven by a chassis- mounted motor.

• To reduce soil and water losses by erosion;

• To reduce the impact of raindrops, protecting the soil againstcompaction and pulverisation of soil aggregates;

• To increase the infiltration rate of water into the soil;

• To stabilise the soil temperature, favouring biologicalprocesses and soil life;

• To conserve soil moisture through the “mulch effect”;

• To act as a nutrient re-cycling agent, ensuring below-groundbiological activity;

• To increase the organic matter in the soil profile, improvingthe CEC and physical structure of the soil;

• To assist in the control of weeds, either by light suppression

or by allelopathy

Figure 6 Maize planted on desiccated residue; soil totally protected against the impact of raindrops and the erosive force of surface runoff This is the key to watershed management.

Sustainable agriculture encompasses various ideas and proceduresand has, as its permanent objectives, the protection of natural resources,maintenance of, or increase in, yields and the reduction of both productionand environmental risks This must also be combined with economic andsocial progress, at the same time guaranteeing the quality of life for thepresent and future generations

The conflicts due to pressure on the utilisation of natural resourcesare exacerbated by increases of population and the demand for food andfibres, more especially in tropical countries In the evaluation of theworld situation, carried out by FAO in its 50th year of existence (1995),

it was established that erosion and other forms of soil degradation areresponsible for an annual loss equivalent to 6 million hectares ofagricultural land (crops, livestock and forests), marginalizing millions

of people

In this time of globalisation, natural resources gain a new dimension,principally in those international relationships expressed in Agenda 21

We all desire development without environmental degradation, a better

quality of life and improved resource availability with the opportunity to

progressively combat social inequalities The great challenge to revertthis situation is in the capacity of society to recuperate and preserve itsvital resources and break the cycle of poverty (which derives fromdegradation of natural resources), opening new opportunities foremployment and trade

The ISO 14000 series, which regulates and harmonises EnvironmentalManagement Systems, is an indicator of how the private sector isprogressing rapidly in the area of environmental law, creating norms and

requirements which authorise the emission of certificates and the use of agreen seal, generating commercial advantages and greater opportunities

to penetrate international markets

In order to achieve sustainability in agriculture it is necessary to satisfythe farmer with demonstrable long term benefit/cost ratios; reduction ofthe high risks deriving from climatic irregularities, more stable yields,lower costs per ton produced and conservation of land and water Themost notable example of this has been Zero Tillage, whose significantexpansion in recent years, as a result of the demonstration effect of itserosion control and many other benefits, coupled with superior profits,make Zero Tillage the best example of sustainable agriculture in Braziland probably, the world

The interest in rational exploitation of Brazil’s natural resourcesextrapolates beyond the nation’s frontiers Besides the qualitative leap ininternal development, this opens up opportunities for internationalpartnerships and their impacts in generating goods and jobs It also permitseconomic and social development at the minimum possible cost, givingsupport to Brazil’s international policies in this context

In natural resources management, a joining of forces is indispensableand education becomes the most important component for motivating thecommunity to learn about, and be motivated by, the future of theenvironment The principal objective of this book is to mobilise supportfrom society as a whole for the efforts of all those engaged in Zero Tillage,

as a sustainable solution to harmonise resourse conservaton with economicwelfare

But, a lack of capitalisation of the farmer results in impoverishment

of natural resources, creating the situation where poverty generates morepoverty In order to break this vicious cycle, it is necessary to provideboth profits and acceptable safety margins for the farmer ZT inhibits thedegradation process by improving the protection of soil and water, resulting

in increasing economic yields In this way, the agricultural sector iscapitalised, ensuring better conditions for the dissemination of practiceswhich protect the environment

Box 2 A true saying

A farmer in the red, cannot conserve the green

Zero Tillage, when undertaken with proper criteria and persistenceover the long term, reduces the risks and improves the sustainability ofagriculture Even in the current situation of under-capitalisation in theagricultural sector and other difficulties and risks in Brazil, the increase

of the area planted to Zero Tillage, which is occurring year after year,denotes the evolution of this system It also generates greater farmerknowledge of, and interest in, Conservation Agriculture through cropmanagement, improvements in soil organic matter, soil life and otheraspects

The encouragement of measures such as Zero Tillage also promotessustainable management for watersheds, by motivating the occupation ofsoil areas with a system of Conservation Agriculture A system of thisnature facilitates complementary government actions, making possiblethe construction-cum-maintenance of works indispensable to this activity,such as reservoirs, river training, re-alignment and maintenance of ruralroads, replanting of gallery forests, dissemination of other conservationpractices and environmental monitoring

The strong demonstrative effect of Zero Tillage has been used toencourage actions oriented towards sustainable agriculture It becamenecessary to establish a strategic plan to guide FEBRAPDP and APDCwhich integrates the interests of agriculture, environment and waterresources, with a view to:

• co-opt the experience, interest, institutional commitment and that

of individuals in the public services to support the expansion ofZT;

• delineate regions and prioritise watersheds with the most criticalsituations in terms of sustainability;

• implement a program for Zero Tillage which would contemplatetraining of technicians and farmers, interchange and furtherdevelopment of technologies already in use, research andenvironmental monitoring;

• articulate joint actions with the public sector, supporting andpromoting the efforts of farmers who practise ZT, incentivatingthem through a system without bureaucracy; this would have thecapacity to interact with the many farmer clubs and associations,led by FEBRAPDP at national level and in the Cerrado region byAPDC

These organisations can structure themselves in line with therequirements of such a programme, providing relevant contributions inthe channelling of efforts, in result demonstrations and in the promotion

of Conservation Agriculture These actions would be oriented towardsthe improvement and conservation of the environment and especially ofwater resources, principally through the multiplication, development andstrengthening of the Clubes Amigos da Terra (CATs or, Friends of theLand Clubs, the grass-roots-level groups for Zero Tillage dissemination).Hundreds of events to disseminate ZT technology (seminars, farmermeetings and field days, research congresses, study tours, etc) have beencarried out in Brazil, including seven national ZT meetings, of which 2organized by APDC in the tropical region ( in Goiânia - 1996 and in

Brasilia - 1998, totalling 4300 participants); see figure 7 This has brought

valuable contributions to the above strategy With the effective

participation of Embrapa, universities and state research institutions, the

lessons learnt will give constant technical support to the implementation

of a programme targeting water and other natural resources through the

conservation of soil and of bio-diversity This would be firmly based on

productive Conservation Agriculture as the principal lever for the services

of extension and private technical assistance in the dissemination of ZeroTillage, founding and strengthening the Clubes Amigos da Terra andsimilar organisations

Figure 7 General view of the demonstration area of the 5 th National Zero Tillage Meetings in Goiânia, Goiás state, June 1996: 30 hectares

of demonstration area and approximately 8,000 visitors, representing

an ntegrated action of the economic agents of technology transfer.

24

CHAPTER I

THE SECOND GREEN REVOLUTION 1

Manoel Henrique Pereira2

1 Based on an update of the opening address given to the 5 th National Zero Tillage Meeting in Goiânia, – Goiás State, Brazil (17- 21 June 1996).

2 President of the Confederation of Associations for Sustainable Agriculture in the Americas (CAAPAS) and (FEBRAPDP) founding president of the Brazilian Federation for Zero Tillage in Crop Residues from 1992-1998.

In the Conventional Tillage system, turning the soil over

inhibits biological processes and de-stabilizes the soil’s physical

structure Zero Tillage reverts this picture.

Beginning effectively in Brazil in 1972, ZT expanded slowly untilthe technology was well-developed, occupying one million hectares inthe 1989/90 agricultural year The critical period had then passed In 1999/

2000, Brazil planted over 14 million hectares (all seasons) Figure 2 showsthis evolution graphically

The ZT system, the target of criticism in its early days and consideredthe privilege of big farmers, has also conquered both small and mediumfarmers Now, it is also used to renovate degraded pastures, and even onpoor native pastures, never before cultivated Zero Tillage has come ofage It is now recognized by all segments of society

The small farmers, with their field events and meetings, with thesupport of state extension services, discuss ZT with animal traction, andeven manual planting methods The large and medium farmers have bynow participated in seven national meetings, held between 1981 and 2000,

in addition to many other local, regional and state meetings And finally,research, which represents the scientific support element in the

development of this technology, has been promulgated in congresses, such

as the First National ZT Congress, in Ponta Grossa, PR (1997)

In the Cerrado (tropical wet/dry Savannah) region, more so than inother regions of Brazil, the soil should be protected, not only from theeffects of water and wind erosion, but also for other motives, which sciencediscovers and the farmer recognises I make special reference to thedependence on organic matter levels, derived from the decomposition ofcrop residues or those of specific cover crops It was exhaustively discussed

in the 5th, 6th and 7th National ZT Meetings that Conventional Tillage – asequence of operations which cultivates and turns the soil over – inhibitsall soil biological processes and destroys soil physical structure, especiallythat of the Cerrado soils The only tool at hand to redress this situation isZero Tillage

Today, ZT is a reality, the technology is available, it has a personality

of its own, receives support from research and extension and is understood

Figure 2 Expansion of the summer-planted Zero Tillage Area in Brazil as a whole and in the tropical region of the country.

population expansion Thus, irrational use of the soil is insane, for any limitation to its productive capacity will cause economic de- stabilization of the farmers and will put the food security of all nations

at risk From this stems the need to give incentives to the farmer in order

to utilize conservation agriculture systems, such as Zero Tillage (Figures

2 and 4) In this address, we proposed to the authorities present at the 5thBrazilian National Zero Tillage Meeting that they promote the positiveeffects which derive from protecting our soils, in parallel with othermeasures, such as the reduction of rural land tax and of the value added

Figure 3 Zero Tillage planting of soya in Paraná state, Brazil, following the harvest of spring wheat.

tax (ICMS) imposed on farm products, in order to give farmers an incentive

to adopt this planting method (i.e Zero Tillage) These incentives cannot

be delayed, since they will save the farmer from the negative impacts ofgovernment economic plans and their disastrous effects on Brazilianagriculture: unpayable debts, machinery almost on the scrap heap andsoil degradation (Figure 3)

Figure 4 Erosion: scars on the face of the farming landscape.

Figure 4 Zero Tillage: protects the soil – man at peace with nature.

CHAPTER 2

Rolf Derpsch 2

“Peace, development and protection of the environment are

interdependent and inseparable” (ECO Rio, 1992).

As a result of the great diversity of definitions which have arisen inrecent years, in this presentation it is necessary to define what is understood

by “sustainable agriculture” This is a system which seeks to establishpermanently high soil productivity in such a way as to conserve theequilibrium of the ecological environment (Adelheim and Kotschi, 1985).Also implied are economic feasibility and improvements in the quality oflife In other words, a sustainable system of agriculture maintains highyields for an indefinite period, without harming either the soil or theenvironment as a whole In short, the aim is to maintain, and/or improve,soil fertility in such a way that future generations can obtain yields equal

to, or higher than, those obtained today, thus permitting them to improvetheir quality of life

1 Based on keynote address at the V Brazilian national ZT Meeting, Goiânia, Goiás, State, Brazil, 17-21 of June 1996., promoted by FEBRAPDP and organised by APDC, with the assistance of Embrapa.

2 At the time advisor to the Soil Conservation Project MAG-GTZ, (Ministério de Agricultura y Ganaderia, Paraguay and German Agency for Technical Cooperation) – Eschborn, Germany P.O Box 1859, Asuncion, Paraguay Current e-mail: rderpsch@quanta.com.py

Definitions of sustainability which consider only one dimension(such as, for example, soil fertility) are inadequate, since environmental,social and economic dimensions should always be included (Hailu andRunge-Metzer, 1993) In synthesis, the term “sustainable” means “forever”, i.e., a system of agriculture programmed to promote permanentregeneration of these dimensions

The soil is the basis for food production and one of the most importantfactors in the environment For the protection of natural resources andfood security for humanity and to guarantee the sustainability ofagricultural production, erosion must be eradicated

Water is a vital element but an exhaustible resource Erosion ofagricultural soil also degrades water quality, which then must be treatedchemically to obtain domestic or industrial water, at a high cost tohumanity

Especially in developing countries, rapid soil degradation and sustainable use of land are both the cause and the consequence ofgeneralized poverty (see Introduction, Fig 1)

non-It is necessary to substitute existing production systems (which arecharacterised by intensive soil cultivation and exposure of the bare soil

to rain, sun and wind) with sustainable production systems based onpermanent soil cover with organic residues, such as, for example, ZeroTillage

The principal problem of conventional agriculture in the tropicsand sub-tropics is loss of soil fertility, which is correlated with the dura-tion of soil exploitation (Figure 1)

Figure 1 Degradation of the soil over time with Conventional Tillage.

Box 1: The Unwritten Laws of Falling Yields

• In tropical and sub-tropical conditions, soil preparation results inmineralization of organic matter at a faster rate than it can be

replaced As a consequence, soil organic matter declines and there

is a long term reduction in crop yields

• The high rainfall intensities which prevail in the tropics and tropics are generally associated (even on land with gentle slopes)with soil losses which exceed the rate of natural regeneration; thisresults in chemical, physical and biological degradation of the soil

sub-and in crop yield depression

• Soil organic matter degradation and erosion cannot be avoided when

tropical and sub-tropical soils are cultivated by ploughing or othermethods of working the soil As a consequence, the sustainability

of agricultural production with Conventional Tillage methods iscompromised

• In other words, the plough and other tillage implements are

antagonistic to sustainable soil use in tropical and sub-tropical regions

Pre-plant soil tillage for crop cultivation is one of the principal causes

of the fall in productivity, as can be seen in figure 2

Figure 2 Consequences of soil tillage in the tropics.

Source: Rolf Derpsch.

EROSION

The effects and consequences of soil tillage, including the indirectones, are analysed in figure 3 The erosion process represents the mostnegative factor for economic sustainability and, also, the factor of thehighest aggression towards the environment Its control is indispensable.The results depicted in Table 1 show clearly that the Zero Tillagesystem not only reduces erosion to a minimum, but also substantiallyincreases the proportion of rainwater which infiltrates into the soil

33Figure 3 Consequences of soil tillage on soil degradation and loss ofproductivity, including indirect effects of conventional agriculture.

1 On the Paraná river between Brazil and Paraguay of 12.600 megawatt capacity and reservoir area of 1350 km2.

Figure 4 Monthly variations of the quantity of sediment

in the water of Itaipú reservoir.

Figure 5 Monthly variations in the level of nitrogen in

the water of Itaipú reservoir.

EFFECTS OF ZERO TILLAGE

ON DIFFERENT SOIL PROPERTIES

Scientific research world-wide shows that Zero Tillage, whencompared to Conventional Tillage using ploughs or offset discs, haspositive effects on soil fertility This occurs because Zero Tillagedrastically reduces erosion to values similar to those of natural soilregeneration and also because Zero Tillage increases the level of organicmatter in the soil

There is a close relationship between organic matter content,agricultural productivity and efficiency of fertilisers (Kotschi & Adelheim,1986) As a result of low values of the Cation Exchange Capacity (CEC -the chemical measure of soil fertility) in the majority of tropical and sub-tropical soils (Sánchez, 1976), the contribution of organic matter to theCEC becomes proportionately much greater In the tropics, this organicmatter is mineralised up to five times faster than in temperate climates(Sánchez and Logan, 1992)

All research demonstrates lower organic matter levels in cultivatedsoils when compared to those under Zero Tillage Figure 6 illustrates therapid decline in soil organic matter when submitted to ConventionalTillage, in the Brazilian Cerrado region (tropical wet/dry savannahs) inthe NW of the state of Bahia (Silva et al, 1994)

Figure 6 Soil organic matter decline in three tropical soils under conventional tillage

Source: Silva et al, 1994.

Zero Tillage has the opposite effect on the organic matter content ofthe soil Even so, the reclamation of an impoverished soil is a slow process,which takes many years

Figure 7 Zero Tillage increases organic matter levels.

In contrast to the Conventional System, Zero Tillage has positive effects

on the most important chemical properties of soils Under the Zero Tillagesystem higher levels of organic matter, Nitrogen, Phosphorus, Potassium,Calcium, Magnesium, and also higher values of pH., with correspondinglylower aluminium levels, are registered (Sidiras & Pavan, 1985)

Comparing the Zero Tillage system with that of Conventional Tillage,the former shows higher infiltration rates (Roth, 1985), which result in anaccentuated reduction of erosion Field research shows higher moisturelevels, lower soil temperatures and also more stable soil aggregates (i.e.improved soil structure) under the Zero Tillage system (Kemper &Derpsch, 1981; Sidiras & Pavan, 1986) At the same time, higher soildensities are registered (Derpsch et al), which many scientists considernegative However, both in Brazil and Paraguay, in spite of the slightlyelevated soil density under Zero Tillage, higher yields are being obtainedwith this system

The non-utilisation of tillage implements, which destroy the “nests”and galleries constructed by the small animals of the soil, means that theZero Tillage system promotes higher soil biological activity The morefavourable moisture and temperature conditions and the increased quantity

of organic matter and crop residues also have a positive effect on the life ofthe flora and fauna in the soil As a result, with Zero Tillage, there are moreearthworms, arthropods (mites, collemboles and insects), micro-organisms(rhizobia, bacteria and actinomycetes) and also fungi and mycorrhiza.(Kemper & Derpsch, 1981; Kronen, 1984; Voss & Sidiras, 1985)

Some diseases increase with Zero Tillage (Igarashi, 1981; Homechin,1984; Reis, 1985; Reis & Santos, 1987; Reis et al, 1988) Therefore, thissystem should not be practised with mono-cropping Generally, a balancedcrop rotation with cover crops is sufficient to neutralise this negative aspect

of Zero Tillage In terms of insect pests, the system shows both positiveand negative effects, depending on the specific pests and variations inclimate over the years As a rule, the diversity of insects, mites and otherlife increases, because in the mulch cover of Zero Tillage they encounterimproved conditions for reproduction The advantage of Zero Tillage isthe creation of favourable conditions for the development of useful insects(predators), thus reactivating equilibrium, with a consequent reduction inthe use of pesticides and agricultural chemical products in general ZeroTillage thus potentialises biological controls and integrated pestmanagement (IPM)

Herbicides: society is concerned with the question of a possible

increase in the use of herbicides in the Zero Tillage system A detailedsurvey undertaken by Bull et al (1993) shows that farmers who plantmaize use approximately the same (total) amount of herbicide in ZeroTillage as compared to Conventional Tillage There is also a consensusamongst farmers who have practised Zero Tillage for many years in theUSA that this system demands less herbicide than Conventional Tillage.The general expectancy of Americans is that the quantity of herbicidesused in Zero Tillage will continue to decline, as more experience is gainedwith the system (Papendick, 1996) This is also the forecast fromexperienced farmers in Brazil, the Argentine and Paraguay, who, throughthe systematic use of cover crops and rotations, allied to proper utilisation

of chemical products, are achieving a reduction in the quantity of herbicides

in Zero Tillage to approximately 80% of the level used in ConventionalTillage Research in Paraguay has shown that, by using short term greenmanure cover crops and always seeding as soon as possible after harvest,

it was possible to reduce herbicide rates to zero for 3 years in a row Atthe same time costs of production were reduced (kliewer et al 2000)

One of the arguments frequently levelled against Zero Tillage – that it requires an increase in the use of herbicides – is thus unfounded, when Zero Tillage is well-managed It should be remembered that, in

Zero Tillage, there is generalised use of two or three desiccant herbicides,not used in Conventional Tillage and which have shown themselves to be

of low toxicity to the environment (Jansen, 1999) Chapter 7 contains anencouraging analysis on the extremely low risk of possible environmentalimpacts of herbicides in Zero Tillage

Effects of agricultural chemicals on earthworms: earthworms are

considered a thermometer of the state of soil fertility In Zero Tillage, anincrease in earthworm number has been noted when compared toConventional Tillage For this reason, it is important to consider the toxiceffect of agricultural chemicals on these annelids Edwards & Bohlen (1995)studied the effect of 193 products on earthworms, of which 32 were classified

as “extremely toxic” or “very toxic.” The highest number of toxic productswas found amongst the carbamate insecticides (9) and organic compounds(6) Amongst the 53 herbicides studied, only two were classified as

“extremely toxic” to earthworms (Chloroacetamide and Pentachlorophenol);there were no herbicides in the “very toxic” class and only three wereclassified as “moderately toxic” (Chlorthiamid, Dinoseb and Simazine).The desiccant herbicides in this study which could be considered specific

to Zero Tillage (Glyphosate and Paraquat) were classified as “non-toxic”.2,4-D was classified as “non-toxic” except at high application rates.Atrazine, Bromacyl, Cyanazine, Dalapon, Diuron, Linuron, MCPA andTrifluralin, were also described as “non-toxic” to earthworms