ISSN 0253-2050 Conservation agriculture Case studies in Latin America and Africa Empirical evidence has been accumulating that sustainable intensification of crop production is technically feasible and economically profitable Added benefits are the improvement of the quality of the natural resources and protection of the environment in currently unimproved or degraded areas, provided farmers participate fully in all stages of technology development and extension This has led to what is called “conservation agriculture” Three criteria, i.e no mechanical soil disturbance, permanent soil cover and crop rotations, distinguish conservation agriculture from a conventional agricultural system This publication demonstrates how conservation agriculture can increase crop production while reducing erosion and reversing soil fertility decline, thus improving rural livelihoods and restoring the environment in developing countries The document is based on testimonies and experiences of farmers and extensionists in Latin America and Africa FAO SOILS BULLETIN 78 Cover photograph by FAO Zero tillage, Argentina Conservation agriculture Case studies in Latin America and Africa FAO SOILS BULLETIN 78 Land and Plant Nutrition Management Service Land and Water Development Division Rome, 2001 The designations employed and the presentation of the material in this information product not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries ISBN 92-5-104625-5 All rights reserved Reproduction and dissemination of material in this information product for educational or other non-commercial purposes are authorized without any prior written permission from the copyright holders provided the source is fully acknowledged Reproduction of material in this information product for resale or other commercial purposes is prohibited without written permission of the copyright holders Applications for such permission should be addressed to the Chief, Publishing and Multimedia Service, Information Division, FAO, Viale delle Terme di Caracalla, 00100 Rome, Italy or by e-mail to copyright@fao.org © FAO 2001 Conservation agriculture – case studies in Latin America and Africa iii Preface The purpose of this publication is to show how conservation agriculture can increase crop production while reducing erosion and reversing soil fertility decline, improving rural livelihoods and restoring the environment in developing countries Soil organic matter and biological activity in the rooting zone, stimulated by continual additions of fresh organic material (crop residues and cover crops) are the basis of conservation agriculture, as described in the first chapter A review of conservation-effective systems of land use in Africa and Latin America is used to present a set of conditions necessary for farming systems to be conservation-effective and sustainable in the long run As described in the second chapter, these experiences have demonstrated that the development of intensive production systems in the tropics is technically feasible and economically profitable, while improving the quality of the natural resources and protecting the environment These production systems allow a more adequate land use, which in turn generate more nutrients in the soil and improve its water retention capacity Additionally, agro-biodiversity and carbon sequestration are enhanced through these conservation-effective systems The farming systems represent a wide range of geographic and resource features and contrasting sociological conditions They include the reduction or elimination of slash and burn in Honduras, the development of minimum tillage and direct drilling practices on small farms in Brazil, the liberation of areas through intensification of the livestock sector in Costa Rica, the mass adoption of zero tillage practices in El Salvador, biomass transfer to increase soil fertility in Kenya, the use of stover for both livestock and conservation purposes in the United Republic of Tanzania, a historical perspective of soil and water conservation in Malawi and the gradual improvement of poor agricultural lands in Ethiopia Farmers have responded rapidly to market opportunities where they have been confident that they can sell their entire produce that is surplus to family requirements As shown in the third chapter, adaptations by farmers, either in their farming system or in the new technology, have to be supported by institutions, extension services, research and policies All cases illustrate the importance of cover crop species in the farming system, but in general these species have not been adequately studied Much research has been weak on socio-economic variables or even ignored them This has often resulted in inappropriate promotional strategies or messages and a poor understanding by policymakers of possibilities for improved use of natural resources In all cases the role and policies of governments have been of crucial importance, particularly with regard to creation of farmers’ groups, land rights, input supply and credit schemes, incentives and penalties, and availability of and accessibility to information The cases demonstrate the need for policy environments, institutions, and practices to be integrated to meet the demand for food, to reduce poverty, and to utilise resources in an environmentally, socially, and financially sustainable way They illustrate the importance of production systems that are capable of continually adapting to changing social, economic and environmental conditions Additionally, the cases show the importance of reliable support facilities to facilitate the transition of farms from subsistence to more intensive systems of farming iv Acknowledgements This publication which was prepared by Alexandra Bot, FAO Consultant, and José Benites, Technical Officer, Land and Plant Nutrition Management Service, is based on interviews with many farmers, scientists, and senior managers of public and private institutions visited in Brazil, Costa Rica, El Salvador, Honduras, Kenya, Malawi, United Republic of Tanzania, Zimbabwe and South Africa These people are involved in ongoing projects of international organizations, such as FAO and the World Bank, or of nongovernmental and governmental organizations in the mentioned countries The authors would particularly like to acknowledge the invaluable help provided by the main collaborators in the countries covered: Telmo Amado (Federal University of Santa Maria, Brazil); Roberto Azofeifa, (FAO, Costa Rica); Bill Berry (KwaZulu-Natal Department of Agriculture and Environmental Affairs, South Africa); Brian Birch (KwaZulu-Natal Department of Agriculture and Environmental Affairs, South Africa); Andreas Böhringer (ICRAF, Malawi); Trent Bunderson (Washington State University, USA); Brian Burgess (Malawi); Mario Chavez (Ministry of Agriculture and Livestock, Costa Rica); Rodney Cheatle (Farmers Own Ltd, Kenya); Ian Cherret (FAO, Honduras); Horacio Chi (Ministry of Agriculture and Livestock, Costa Rica); Christina Choto (Centro de Tecnología Agrícola, Ministerio de Agricultura y Ganadería, El Salvador); Edward Chuma (Institute for Environmental Studies, Zimbabwe); William Critchley (Vrije Universiteit Amsterdam, The Netherlands); Diógenes Cubero (FAO, Costa Rica); Pieter Dercksen (FAO, Costa Rica); Michelle Deugd (FAO, Honduras); Hinton Estates (Agriway, Zimbabwe); Jim Findlay (Agrecon Consultants, South Africa); German Flores (Lempirasur, Honduras); Valdemar Hercilio de Freitas (EPAGRI, Brazil); Jorge Garay (Lempirasur, Honduras); Amadu Hiang (ICRAF, Kenya); John Landers (Associação de Plantio Direto no Cerrado, Brazil); Wilfred Mariki (Selian Agricultural Research Institute, Tanzania); Nicholaus Massawe (Selian Agricultural Research Institute, Tanzania); João Mielniczuk (University of Porto Alegre, Brazil); Vincent Mkandawire (Ministry of Agriculture and Irrigation, Malawi); Osmar de Moraes (EPAGRI, Brazil); Ant Muirhead (No Till Club, South Africa); Qureish Noordin (ICRAF, Kenya); Alan Norton (Agriway, Zimbabwe); Brian Oldreive (Agriway, Zimbabwe); José Miguel Reichert (Federal University of Santa Maria, Brazil); Bill Russell (No Till Club, South Africa); Gustavo Sain (CIMMYT, Costa Rica); Milton da Veiga (EPAGRI, Brazil); Jan van Wambeke (FAO, El Salvador); Richard Winkfield (Agricultural Research Trust, Zimbabwe) Several people contributed to the development of this publication The authors would like to acknowledge the assistance of Francis Shaxson, Richard Fowler, Romualdo Hernández, Paul Mueller, Rob van Haarlem and Willem Hoogmoed The valuable comments provided by Robert Brinkman, Sally Bunning, Rudy Dudal, Theodor Friedrich and Petra van de Kop on draft versions of the document are highly appreciated In the production of this publication, the authors have been effectively assisted by Sandrine Vaneph and Lynette Chalk-Contreras Conservation agriculture – case studies in Latin America and Africa v Contents PREFACE III ACKNOWLEDGEMENTS IV ACRONYMS VI INTRODUCTION CONCEPTS AND IMPACTS OF CONSERVATION AGRICULTURE Concepts Changing mentalities Combating land degradation and improvement of land productivity Socio-economic advantages Impacts on the environment Impact of management practices on soil fauna and soil fertility Mitigating climate changes and greenhouse gases Reduction of contamination and water pollution Enhancement of biodiversity Less vulnerability to natural disasters 7 10 12 13 14 16 17 18 18 RURAL COMMUNITIES ACTIVELY IMPLEMENTING CONSERVATION AGRICULTURE Organization: the role of farmers’ groups and non-governmental organizations Implementing conservation agriculture practices 21 ENABLING COMMUNITY-BASED PROJECTS Appropriate scenarios for conservation agriculture Designing community-based projects: tools and practices Involvement of all stakeholders Institutional and policy considerations Laws and regulations Incentives and restrictions Land tenure Conservation agriculture linkages with international initiatives 33 34 34 37 39 41 42 44 46 CONCLUSIONS 49 REFERENCES 51 ANNEX KEY CONCEPTS AND DEFINITIONS 55 ANNEX THE SOIL ECOSYSTEM 63 22 24 vi List of boxes Page 10 11 12 13 14 15 16 17 18 19 20 21 Principles of conservation agriculture Key features of conservation agriculture systems Agro-environmental features of conservation agriculture Reasons for the slow research response to zero tillage in Brazil prior to 1995 Conservation structures and practices in southern Brazil Farmers’ benefits – Lempira (Honduras) Conservation of time and energy The farmers’ point of view – Lempira (Honduras) Soil microbial communities and zero tillage Nutrients availability under various cover crops (southern Brazil) Carbon sequestration (southern Brazil) Increase of protected areas through livestock management (Costa Rica) Indigenous knowledge and empowerment in Africa The Quesungual agroforestry system – Lempira (Honduras) The Zero Tillage Association for the Tropics (ZTAT), Brazil Clubes amigos de Terra (CAT), Brazil The Association for Better Land Husbandry (ABLH), Kenya Improved fallow with legumes Improving conservation agriculture (southern Brazil) The shifting cultivation system (northern Brazil) Conservation agriculture based on minimum tillage and animal production in east Africa 22 Crop selection for high residue production – Guaymango, El Salvador 23 Better management and use of crop residues (northern Tanzania) 24 Improving soil fertility (southern Ethiopia) 25 Supporting farmers’ land literacy (Zimbabwe) 26 Trash lines and banana mulching: farmers’ innovations (Uganda) 27 The SADC-ICRAF Zambezi basin agroforestry project 28 Conservation tillage – technology transfer in Kwa Zulu-Natal (South Africa) 29 The Malawi agroforestry extension project (MAFE) 30 Contribution of the Brazilian government to zero tillage promotion 31 History of a soil conservation law (Malawi) 32 Law 7779 “The use, management and conservation of soils” (Costa Rica) 33 The adoption process – Guaymango (El Salvador) 34 Sustainability through incentives: Paraná 12 meses, Brazil 35 The benefits of communal tenure 36 The African Conservation Tillage network (ACT) 11 12 13 14 15 16 17 18 22 23 23 24 25 27 27 28 30 30 31 31 36 37 38 39 40 40 41 42 44 44 46 47 Conservation agriculture – case studies in Latin America and Africa vii List of plates Page 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Continuous cultivation damages the vital but fragile ecosystem of soil flora and fauna Soybean grown under conservation agriculture in Brazil Smallholder coffee farmers covering the soil with straw to preserve moisture, Malawi The use of tied ridges to catch and guide run-off and prevent damage to the crops Land preparation is by far the most time-consuming activity for the farmer and family Only a small percentage of the total area is worked in reduced tillage systems Flooding and sediment transport to the reiver increasing cost of water treatment The Quesungual system is an indigenous agroforestry system which most distinct characteristic is the combination of naturally regenerated and pruned trees and shrubs with more traditional agroforestry components, such as high value timber and fruit trees In between the trees the traditional staple crops, i.e maize, sorghum and beans are grown Maasai, traditionally herding cattle, are engaging in vegetable growing activities to increase their income and spread the risks A historic moment: this meeting of farmers, technicians, and municipal leaders from Agrolandia, micro-catchment Ribeirao das Pedras, first discussed how to convert traditional animal traction equiment to direct-sowing equipment A Kenyan farmer in front of his Tithonia hedge, which is cut and used to fertilize his sukumawiki crop Flowering wild sunflower, Tithonia, now a roadside weed in Kenya and the United Republic of Tanzania, which is used as green manure in western Kenya Implements have been adapted for resource-poor farmers: a herbicide spray, which can be drawn either manually or by animals The knife-roller bends over or crushes the cover vegetation, preparing the land for the succeeding crop, which will be sown through the residues Simple seed drill, which can cope well with the enormous amount of crop residues left in the field First introduction of an animal-drawn direct seeder in a Maasai village in northern United Republic of Tanzania Stripping maize to separate palatable and non-palatable parts to be used respectively for animal fodder and soil improvement Drawings explaining box baling of maize stover Discussing and thinking about the future, and planning together Farmer explaining to his neighbours the functioning of a new implement Imitation of the erosive effect of rainfall on bare soil and on a soil covered with residues Banana mulching, a common practice to prevent soil moisture to evaporate and keeping the bananas productive for a longer period Free-roaming cattle often lead to conflicts between pastoralists and agriculturalists 10 13 14 18 19 22 24 26 26 28 29 29 29 30 31 35 36 37 38 45 viii List of tables Page Common practices and consequences of conventional agriculture 2 Total area - in hectares - under no-tillage in different countries in the seventies, eighties and in1999/2000 Water, soil and plant nutrient losses under conventional agriculture and direct seeding in a wheat-maize rotation 16 List of figures Page Production increase of maize and sorghum under the Quesungual system 12 Population size of root nodule bacteria under zero tillage 15 Maize production under the Quesungual system 19 Yield of maize-sorghum system in Guaymango, 1963 - 1989 34 Reduction in burning over the last three years in southern Lempira 43 Conservation agriculture – case studies in Latin America and Africa 57 The encouragement of better land husbandry and the underlying philosophy suggest that conservation of water and soil is best achieved by promoting local land management strategies that benefit both the land user and the soil Better land husbandry strategies (which may include planning of more-appropriate land uses and their management) enhance the soil’s regenerative capacities to improve the vitality and resilience of the total soil ecosystem Better land husbandry manages soil organic matter and creates and maintains favourable soil structure, rather than merely preventing physical loss of water and soil It also embraces a better matching of uses with management, at several scales, of broader landscape characteristics which help maintain other essential ecosystem services in particular the hydrological and nutrient cycles SOME KINDS OF AGRICULTURE Agriculture is based on changing a natural ecosystem to create a new habitat in which the plants and animals, which produce food and other requirements for humans, can thrive The underpinning resources such as soil and water are managed on a basis that aims to maintain the long-term productive capacity of the new environment The history of humankind lists our attempts and failures in maintaining sustainable systems As long ago as 000 BC, villages in central Jordan were being abandoned after approximately 000 years in response to soil erosion associated with deforestation and poorly managed land, declining crop yields, and the inability to continue to feed the community Modern agriculture continues to affect the environment and humankind Agricultural production systems in use today form a major part of environmental management in various ways The major production systems can be classified as: intensive cropping, rainfed cropping, shifting agriculture, agroforestry, agropastoral, plantation and forest extraction Intensive cropping systems are based on high productivity, including monoculture, mechanisation, chemical inputs, biotechnology and irrigation These systems may lead to degradation of natural resources if not managed appropriately, particularly through declining biodiversity Rainfed cropping systems are based on annual plant species, and are commonly integrated with livestock production Crop rotation is employed to manage soil fertility yet these areas are commonly fragile and their intensification can easily lead to degradation of the natural resource base Shifting agriculture is based on the clearing of land to prepare a cultivation plot and subsequently abandoning this to re-growth and eventual natural reforestation It is a stable form of agriculture under low population density regimes, but rising population density decreases the re-growth time available for forests and leads to this system becoming unsustainable Some shifting agriculture has evolved into sophisticated agroforestry management systems while in others it continues to be practised in response to poor land tenure policies Agroforestry involves cultivation of perennial and annual crops together in a sustainable manner and is increasingly practised on degraded areas The practice brings environmental benefits through soil protection and efficiency of utilisation of water and soil nutrients It also creates a wider diversity of environments for wildlife and other fauna Local knowledge concerning the utility of native species could be mixed with scientific information to develop future farming systems Annex - Key concepts and definitions 58 Agropastoral systems represent a variety of systems suited to resource poor or degraded areas and can impact severely on the natural resource base through overgrazing More sustainable systems have to be developed, such as the integration of grazing livestock on small farms or the introduction of new pasture species with associated management inputs, and There is a clear need for more knowledge of traditional animal breeds Plantation systems are associated with such products as coffee, tea, palm oil, timber and rubber These systems are based on clearing of native forests and are commonly monocultures However, in some cases, perennial tree crops are also suitable for rehabilitation of degraded soils Forest extraction continues as farmers seek new lands and timber prices encourage exploitation of remaining native forests The trend of large-scale forest destruction appears to have been reversed in more developed countries with a reliance on plantation forestry, although extraction continues in less developed countries SUSTAINABLE AGRICULTURE Sustainability is a term that has come into widespread use, particularly during the past decade Its use has been so extensive and it has been applied to so many distinct circumstances that it has come to be interpreted in many different ways Some people have applied it to an unchanging system of production or to a lifestyle that can be perpetuated indefinitely Such a static interpretation is inappropriate for farming systems The basic challenge for sustainable agriculture is to make better use of available biophysical and human resources, by minimizing the use of external inputs, by optimizing the use of internal resources, or by combinations of both (Pretty and Shaxson, 1998) Sustainable agriculture seeks the integrated use of a wide range of technologies in soil and water, nutrient and pest management, and agroforestry A more sustainable agriculture, therefore, pursues: • a thorough incorporation of natural processes such as nutrient cycling, nitrogen fixation, soil self-regeneration and pest-predator relationships; • a minimisation of the use of external and non-renewable inputs that damage the environment or harm the health of farmers and consumers Sustainable forms of agriculture can be achieved through: • the full participation of farmers and rural people in all processes of problem analysis, technology development, adaptation and extension, and monitoring and evaluation; • a greater productive use of local knowledge, practices and resources; • the incorporation of a diversity of natural resources and enterprises within farms; • an increase in self-reliance amongst farmers and rural communities CONSERVATION AGRICULTURE The practical implementation of the principles and objectives of sustainable agriculture requires a technical tool that would change effectively from a conventional agricultural technology that Conservation agriculture – case studies in Latin America and Africa 59 exploits the soil and as a result may destroy its natural ecosystem functions, to a conservationist approach that conserves, and even regenerates the soil properties and the ecological processes and functions of the soil and its biota This technical tool is called “conservation agriculture” Conservation agriculture, as described in this report, derives from experiences with reduced – and zero-tillage – but is set out as an umbrella term that connotes systems of plant production – whether from crops, pastures, trees alone or in combination – which aim to satisfy the above criteria on a continuing basis, achieving both stable production as well as effective conservation and optimum use of water and soil components It anticipates synergistic benefits that arise from combining the dynamics of improved soil productivity processes with the latent skills and enthusiasms of farmers and their rural families, the joint keys to sustainability Conservation agriculture is in fact widening the concept of better land husbandry including besides the husbandry of land and water resources also husbandry of crops, animals and other natural resources allowing the sustainable system to be commercially productive The techniques that are involved minimise or avoid soil-damaging effects often associated with conventional tillage-based crop production methods, particularly in tropical zones Conservation agriculture in this way is able to control the problems of land degradation even under critical climatic conditions Infiltration of rainwater is increased (Roth 1985) With this the soil erosion is reduced to a level below the regeneration rate of the soil and the groundwater resources are maintained or enhanced (Derpsch 1997) Leaching of soil nutrients or farm chemicals into the aquifer is also reduced (Becker 1997) compared to conventional arable agriculture The system depends on biological processes to work and thus it enhances the biodiversity in an agricultural production system at a micro- as well as macro scale including flora and fauna It increases soil organic matter contents in agricultural soils in the absence of soil tillage, turning agricultural land into a sink for carbon, thus contributing to carbon sequestration (Schlesinger 1999) The benefits arising from conservation agriculture have caught the attention of individual farmers, groups within rural communities, and local authorities They have noted greater stability of agricultural production and security of livelihoods in the face of strong variations in climate and markets; improved availability – in quantity and duration – of groundwater and streamflow At the same time this has reduced amounts of government funds – from local and national authorities – to be allocated for maintenance and repairs of roads and bridges, for recuperation of flood damage and for drought relief A consequence has been that greater proportions of their limited funds can be applied to making positive improvements in other social services and infrastructure such as facilities for health, education and public transport The “conservation agriculture approach” already has been put into practice on a large scale, and it has become clear that the increased resilience of the land and soil systems has several other positive effects: • by improving land capabilities, it permits greater flexibility of land use in the present while also maintaining wide options for varied land uses in the future; • by increasing security of rural livelihoods, it has also reduced the despair-driven rate of ruralto-urban migration; • infrequent climatic events of a given severity cause considerably less damage in such areas than they would have done under conventional tillage systems; Annex - Key concepts and definitions 60 • the need for (often ineffective) restrictive and punitive legislation concerned with land use and management at national level becomes much less apparent, while those laws which assist local communities in framing and formalising their own encouragement and regulations become positively effective; • it enhances local capacities to better what they are already doing, at community level both of organisms within the soil and at farmer-level above it; • it appears capable of achieving sequestration of atmospheric CO2 into useful forms within agriculture; • it achieves effective conservation of water and soil by stealth within production systems rather than by frontal attack independently of them CONSERVATION TILLAGE The term conservation tillage is properly used for all types of tillage that are designed to minimise erosion, for example contour ploughing The term is not a synonym for conservation agriculture, therefore, since this is based on not disturbing the soil by tillage at all, or the minimum feasible extent However, on several occasions the term conservation tillage has been used to denote conservation agriculture In this report, the term has been avoided whenever possible When it does occur, the context should clarify the meaning of the term Crop residue mulching A technology whereby at the time of crop emergence at least 30 percent of the soil surface is covered by residues of the previous crop (Erenstein, 1999) Direct planting/seeding This is only a technique that refers to seeding/planting without ploughing or cultivation to prepare a seedbed The same equipment is used in Conservation Agriculture However, the term direct seeding can also be used for implements that combine primary and secondary tillage and seeding in one machine-tractor operation Organic agriculture Organic agriculture is not a synonym of Conservation Agriculture (CA), as CA does not prohibit the use of farm chemical inputs but allows an adapted use of them However, in some cases organic farming can be practised within the CA framework Residue farming In residue farming, the residue or stubble from the previous crop is not ploughed under Instead, it is left undisturbed (in place) to protect the soil surface and conserve soil moisture The seeds are chiselled in between the stubble and the seedlings are allowed to sprout through the decomposing vegetative residue Weeds are controlled by biodegradable herbicides Conservation agriculture – case studies in Latin America and Africa 61 Zero tillage Zero tillage is adapted to small, medium and large farmers, using hand planting methods, animal traction or mechanised planting/sowing A characterisation of zero tillage follows (Landers, 2000): • Crop residues are distributed evenly and left on the soil surface; • No implements are used to turn the soil over, cultivate it or incorporate crop residues; • Weeds and purpose-planted cover crops are controlled by a pre-plant application of a nonpollutant desiccant herbicide; • A specialised planter or drill cuts through the desiccated cover and residues accumulated on the soil surface, slotting seed (and fertilizer) into the soil with minimal disturbance; • Subsequent weed control is carried out with some pre-but mostly with post-emergent herbicides also used in conventional tillage; • Crop rotation is fundamental to zero tillage, since this promotes adequate biomass levels for permanent mulch cover, assists in control of weeds, pests and diseases, recycles nutrients and ameliorates soil physical conditions; • Soil erosion is reduced by about 90 percent and soil biological activity and bio-diversity maximized REFERENCES Becker, H 1997 Research gives Clues to Reduce Herbicide Leaching; US Agricultural Research Service Press Release, 1997 Derpsch, R 1997 Importancia de la Siembra Directa para obtener la Sustentabilitdad de la Producción Agrícola; V Congreso Nacional de Siembra Directa de AAPRESID, Mar del Plata, Argentina Erenstein, O.C.A 1999 The economics of soil conservation in developing countries: the case of crop residue mulching Thesis Wageningen University 301p Landers, J N 2000 Case study for Wageningen University: Zero tillage development in tropical Brazil The story of a successful NGO activity 37 pp Unpublished document Mollison, B and Slay, R.M 1991 Introduction of Permaculture The Tutorial Press, Harare, Zimbabwe 198p Pretty, J and Shaxson, F 1998 The potential of sustainable agriculture Paper prepared for the DfID Natural Resources Advisors Conference, July, 1997 ENABLE Newsletter of the Association for better Land Husbandry, No Roth, C.H 1985 Infiltrabilität von Latosolo-Roxo-Böden in Nordparaná, Brasilien, in Feldversuchen zur Erosionskontrolle mit verschiedenen Bodenbearbeitungs-systemen und Rotationen Göttinger Bodenkundliche Berichte, 83: 1-104 Shaxson, T.F 1993 Conservation effectiveness of farmers’ actions: a criterion of good land husbandry In: Topics in Applied Resource management in the Tropics E Baum, P Wolff, M Zobich (Eds.) Vol 3: ‘’Acceptance of Soil and Water Conservation: Strategies and Technologies” Witzenhausem (Germany): Deutsche Inst Fur Trop Und Subtrop Landwirt./DITSL pp.103-128 62 Annex - Key concepts and definitions Shaxson, T.F 1997 Soil Erosion and Land Husbandry Land Husbandry, Volume 2(1):1-14 Shaxson, T F, Hudson, N.W., Sanders, D.W., Roose, E Moldenhauer, W.C 1989 Land Husbandry: A Framework for Soil and Water Conservation Ankeny (USA): Soil & Water Conservation Society 64p Shaxson, T.F., Tiffen, M., Wood, A and Turton, C 1999 Better Land Husbandry: Re-Thinking Approaches to Land Improvement and the Conservation of Water and Soil Natural Resource Perspectives no 19, June 1997 London: ODI Overseas Development Institute Home Page Conservation agriculture – case studies in Latin America and Africa 63 Annex The soil ecosystem “After two to three days without rains, the ground became very dry and even the weeds would not grow.” Resource-poor farmer in El Salvador The soil ecosystem can be defined as an interdependent life-support system composed of air, water, minerals, and macro- and micro-organisms These organisms can in turn be distinguished into flora (for example plants and micro-flora such as algae, bacteria and fungi) and fauna (for example earthworms, millipedes, woodlice, slugs and snails, and micro-fauna such as protozoa and nematodes) (Brussaard and Juma, 1995) This soil biota, one of the most important components of the soil, plays a major role in many essential natural processes, which determine nutrient recycling and nutrient and water availability for agricultural productivity THE SOIL STRUCTURE BOX A1 Roles of the soil ecosystem A healthy soil ecosystem will: • Decompose organic matter into humus; • Retain nitrogen and other plant nutrients; • Glue soil particles together and create pores for best passage of air and water; • Protect roots from diseases and parasites; • • Make available nutrients to the plant; • Retain water Produce hormones that help plants grow; The arrangement of the solid particles and spaces commonly referred to as soil structure is highly complex and dynamic It depends on its components and their physical, chemical and biological interactions Of special importance are soil texture (particle size distribution); chemical composition and charge distribution of minerals; organic components (humus, humic substances, organic acids etc.; the actions of roots, soil fauna and flora; the physical and chemical action of water; temperature; various forces of aggregation and disaggregation; etc Through these actions, soil components are mixed, aggregated or separated, and a complex of solid materials and pores is created where air, water and nutrients can circulate and be stored, and where roots, animals and micro-organisms develop Its present condition may be altered – all too often degraded – by inappropriate management, which results in compaction, pulverisation and interstitial sealing The physical arrangement of the spaces or pore is where most of the important changes take place: water movement, root extension and enlargement, gas exchange, particularly of oxygen and carbon dioxide in the processes of respiration by roots and micro-organisms Therefore emphasis should be given on the spaces more than on the solid particles because of their critical relationship with soil moisture in soil-water-plant relationships and dynamics The roles of organic matter, roots and soil fauna are most important in the development of pores, and thus for air, water and nutrients circulation 64 Annex - The soil ecosystem NATURAL CYCLES: AIR, WATER, NUTRIENTS Soil water Water is critical to crop production in many areas, especially in Africa There are arid or semiarid areas in all continents, and even in areas with adequate average rainfall droughts or dry spells frequently occur The amount of rainwater that infiltrates depends on the nature of the soil surface and the capacity of the soil to retain and transport water After infiltration, some of this water percolates downwards (and is eventually stored in the groundwater), some is absorbed by plants and released into the air, some evaporates from the soil surface, and the rest is stored as bound water Water in the soil is important for plants and soil life (water and nutrient supply) and for soil genesis (weathering, humus, movement of particles, etc.) Soil water is a vehicle for nutrients and is necessary for biological and chemical reactions in the soil, which build in particular the soil fertility Organic matter plays an important role in the water cycle as it facilitates infiltration and water storage, structure building for water circulation and production of colloids which retain water Micro- and macro-organisms also play major role in creating pores and various forms of organic matter Soil air Air is necessary for the respiration of soil fauna and flora, including plant roots It also plays an important role in chemical reactions The composition of the soil air is different from that of the atmosphere The respiration of roots and other organisms results in the CO2 content of soil air in the surface soil being about ten times that of the atmosphere (Schroeder, 1984) Exchanges between soil air and atmosphere (soil respiration) are through diffusion, depending on the CO2 and O2 pressures and the permeability of the soil (in turn affected by soil structure and water content) In the soil, water and air use the same channels, the pores Air and water share the same spaces; some air can be dissolved in soil water and some can also be stored in the larger pores not occupied by water, often those resulting from the activities of macrofauna or decay of roots Nutrient cycles The main nutrient cycles (especially the nitrogen cycle) in the soil are linked with the activity and cycles of soil life, for example organic matter decomposition, production of organic acids, nitrogen fixation The decomposition of the soil organic matter is called mineralisation and produces primarily simple forms of nutrients containing nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S) The weathering of soil minerals can also release K, Ca, Mg and iron (Fe) Carbon (C), which represents around 47 percent of the dry mass of organic matter, is released into the atmosphere through respiration Water and energy are also produced during these processes A portion of the nutrients present in the soil may be found in the soil water, circulating and being taken up by plant roots and soil organisms Some are lost through leaching or as gases (for example NH3); but an important part is stored on organic or mineral surfaces at anionic and Conservation agriculture – case studies in Latin America and Africa 65 cationic binding sites depending on soil properties (especially cation exchange capacity CEC), pH, concentrations in soil solution, etc These nutrients can be released into the soil solution where the concentration or the pH diminish, for example adjacent to roots These nutrient exchanges between organic matter, water and soil affect soil fertility and need to be maintained, especially for production purposes If the soil is exploited for crop production (export of nutrients) without restoring the organic matter and nutrient contents and keeping a good structure, the cycles are broken and soil fertility declines THE ORGANIC MATTER The decomposition process Decomposition is the physical breakdown and biochemical transformation by saprophytic fungi and bacteria1 of complex organic molecules of dead material into simpler organic and inorganic molecules, which may be used again by other organisms (Juma, 1998) In general bacteria break down readily decomposable organic material, which results in nutrients such as especially N, P and S becoming available for uptake by other organisms This process is called mineralisation2 The waste products from bacteria become soil organic matter This waste material is less decomposable than the original plant and animal material, but can be used by a large number of other organisms Fungi break down the less decomposable organic matter and retain those nutrients in the soil as fungal biomass Just like bacteria, fungal waste products become soil organic matter, and these waste materials are used by other organisms Less resistant plant materials are broken down first, whereas the breakdown of more resistant materials, such as lignin and protein, takes place in several stages The decomposition process can take part in aerobic or in anaerobic conditions Humus: composition and role Subsequent decomposition of dead material and modified organic matter results in the formation of more complex organic matter, called humus (Juma, 1998) This process is called humification Humus consists of a group of humic substances that includes humic acids, fulvic acids, hymatomelanic acids and humins (Tan, 1994) and is probably the most widely distributed organic carbon-containing material in terrestrial and aquatic environments One of the most striking characteristics of humic substances is their ability to interact with metal ions, oxides, hydroxides, minerals and organics, including toxic pollutants, to form watersoluble and water-insoluble associations Through the formation of these complexes, humic substances can dissolve, mobilise and transport metals and organics in soils and waters, or bring about an accumulation in certain soil horizons An example of the former is their effect on nutrient availability, especially those present at micro-concentrations only (Schnitzer, 1986); while an example of the latter is their ability to reduce the toxicity of, for instance aluminium in acid soils (Tan and Binger, 1986) or to capture pollutants such as herbicides (such as atrazine) or insecticides (such as tefluthrin) in the cavities of the humic substances (Vermeer, 1996) Organic C +O2 microbial biomass + CO2 Organic N NH4+ Nitrosomonas àNO2- Nitrobacter NO3- Annex - The soil ecosystem 66 Humic substances enhance plant growth directly through physiological and nutritional effects Thus humic acid is capable of improving seed germination, root initiation and uptake of plant nutrients, and serves as a source of nitrogen, phosphorus and sulphur (Tan, 1994; Schnitzer, 1986) Indirectly, they may affect plant growth through modifications of physical, chemical and biological properties of the soil, such as an increase in water holding capacity and cation exchange capacity, and improvement of tilth and aeration through good soil structure (Stevenson, 1994) THE SOIL LIFE Predator-prey relationships: a source of nitrogen As in all ecosystems, feeding relationships between organisms also exist in the soil Energy is transferred from the primary producers (green plants) through a series of organisms that eat and are eaten, starting with bacteria and fungi, which feed on organic matter (primary consumers) The main effect of this soil activity is the release of nitrogen for plant growth Protozoa are one-celled, highly mobile organisms that feed on bacteria and on each other Because protozoa require five to ten-fold less nitrogen than bacteria, N is released when a protozoan eats a bacterium The released N is then available plant uptake Between 40 and 80 percent of the N in plants can come from the predator-prey interaction of protozoa with bacteria Nematodes are tiny, worm-like, multicellular organisms, which live in the maze of interconnected pores in the soil They move in the films of water that adhere to soil particles Beneficial nematodes eat bacteria, fungi and other nematodes Nematodes need even less nitrogen than protozoa, between 10 and 100 times less than the equivalent live mass of bacteria, or between and 50 times less than the equivalent weight of fungal hyphae Thus when nematodes eat bacteria or fungi, nitrogen is released and becomes available for plant growth Micro-arthropods have several functions They chew plant leaf material, roots, stems and tree trunks into smaller pieces, making it easier for bacteria and fungi to find the food they like on the newly exposed surfaces Arthropods can increase decomposition rates by two to 100 times, although if the bacteria and fungi are lacking, increased decomposition will not occur In many cases however, the arthropods carry around an inoculum of bacteria and fungi, making certain the food they want is inoculated onto the newly exposed surfaces The arthropods then feed on the bacteria and fungi and, because the C/N ratio of arthropods is many times higher than that of the bacteria and fungi, release nitrogen, which is then available for plant growth Earthworms: the soil managers Large soil organisms such as earthworms mix plant material into the soil Three groups of earthworms can be distinguished (Edwards and Lofty, 1977): • Epigeic earthworms, which live in the superficial soil layers and feed on undecomposed plant litter They are usually small and produce new generations rapidly • Endogeic earthworms, which forage below the soil surface in horizontal, connecting burrows These species ingest large amounts of soil, showing a preference for soil rich in organic matter They may have a major impact on the decomposition of dead plant roots Conservation agriculture – case studies in Latin America and Africa 67 PLATE A2.1 Earthworm casts contain up to four times more nitrogen than the surrounding soil, and earthworm burrowing activity improves water and air exchange within the soil [A Odoul/FAO/17749] • Anecic earthworms, which build permanent, vertical burrows that extend deep into the soil This type of worm comes to the surface to feed on manure, leaf litter, and other organic matter They have profound effects on decomposition of organic matter and the formation of soil The burrowing activity of earthworms provides channels for air and water, which has an important effect on the oxygen diffusion in the root zone, and the drainage of water from it The shallow-dwelling earthworms create numerous channels throughout the topsoil, which increases overall porosity The large vertical channels created by the deep-burrowing earthworms greatly increase water infiltration under intense rainfall or ponding conditions Earthworms can also aid extensive root growth in the subsoil, due to higher nitrogen availability in the casts (up to four times more total nitrogen than in the topsoil) and easier penetration into the soil through existing channels (Plate A2.1) Plant-micro-organism interactions Plant roots anchor the plant to the ground and absorb water and nutrients They also create a distinct ecosystem that can profoundly alter plant growth This often-neglected ecosystem is the rhizosphere, which is the outer part of the root and the area immediately adjacent to it A large number of micro-organisms congregate around the surfaces of plant roots They are attracted to the root surface because of chemical compounds secreted by live roots, which are vital sources of food and energy for the micro-organisms These root exudates can be distinguished into three groups (Jackson, 1993): • mucigel, a gel-like material, being a mixture of polysaccharides, proteins, lipids, vitamins and plant hormones enveloping especially the root tips; • a variety of other amino acids, organic acids and simple sugars excreted by the root hairs; • cellular organic substances produced by senescence of the root epidermis The microbes that inhabit the rhizosphere are a mixture of beneficial, neutral and harmful organisms The majority of the micro-organisms are beneficial The microbes in the rhizosphere extract nutrients and energy from the root and its products In return, some of the products of the micro-organisms regulate plant growth This regulation is affected by environmental factors (biological, chemical and physical) which, together with factors such as the species of the plant and its age etc., also affect the mix and concentration of micro-organisms surrounding a particular root Annex - The soil ecosystem 68 PLATE A2.2 Symbiotic bacteria, chiefly associated with leguminous plants and occurring in root nodules, enrich soils by adding nitrogen, a key plant nutrient Nodules containing bacteria on the roots of a Vetch plant [T.F Shaxson] Some examples of beneficial micro-organisms and their functions are Rhizobium and Mycorrhizae The roots of leguminous plants can be infected by Rhizobium bacteria: when a root hair comes into contact with a bacterium, the root hair curls and the cell walls dissolve under influence of enzymes, thus forming a nodule (Plate A2.2) Once inside the nodule the bacterium obtains its necessary nutrients from the host plant and in turn the host plant receives nitrogen compounds produced by the bacteria from nitrogen gas in the soil atmosphere An association with mutual benefits is called a symbiosis, hence the name symbiotic nitrogen fixation3 Mycorrhizae are fungi that form a network of mycelia or threads on the roots and extend the surface area of the roots They grow in the younger roots, as in mature roots the cortex is broken away Fine roots are the primary sites of mycorrhizal development as they are the most active sites for nutrient uptake The roots of most plants are infected with mycorrhizal fungi This symbiotic association between certain groups of soil fungi and plant roots enhances plant growth by enabling a greater proportion of the available nutrients and water in the soil to be absorbed by the plant The benefits of effective association include protection against some root pathogens, increased disease tolerance, drought tolerance and protection against soil toxicity and high temperatures There are several mechanisms of protection through Mycorrhizae (Linderman, 1994): • secretion of antibiotics inhibitory to pathogens; • sheath acts as a physical barrier to penetration; • surplus nutrients in the root are utilised, thereby reducing the amount of nutrients available to the pathogen; • sheath supports a protective rhizosphere microbial population Like other fungi, Mycorrhizae also improve the soil structure by binding soil particles into more stable aggregates with mycorrhizal hyphae The hyphae bind individual clay particles into aggregates, thereby allowing more oxygen to reach the root zone This promotes the rapid multiplication of beneficial aerobic bacteria, which may fix nitrogen, solubilize phosphorus, and process other elements into forms that plants can use As the fungi are also aerobic organisms, this forming of clay soil into a granular structure will also improve their own oxygen supply The fungal hyphae will also bind together sand, which then becomes a better moisture-holding environment for plant roots and bacteria Symbiotic nitrogen fixation: N2 (atmosphere) Rhizobium N organic (soil) Conservation agriculture – case studies in Latin America and Africa 69 Mycorrhizae can form a hyphae-linked underground network to “borrow” nutrients from older trees to feed young seedlings Plant-parasitic organisms In contrast to the beneficial soil micro-organisms, other soil micro-organisms are pathogenic to plants and may cause considerable damage to crops Large numbers of pathogenic microorganisms are normally present in the soil and many of them can infect plant roots However, certain micro-organisms present in the soil are antagonistic to these pathogens and can prevent the infection, as in case of the Myccorhizae Plant-parasitic nematodes are found in association with most plants Some are endoparasitic: living and feeding within plant tissue, while others are ectoparasitic: feeding externally through plant walls The former can kill or reduce plant productivity, while the latter can provide an entry point for disease-causing fungi and bacteria Root-feeding nematodes are very opportunistic and are among the first organisms to invade a volume of soil REFERENCES Brussaard, L and Juma, N.G 1995 Organisms and humus in soils In: A Piccolo (Ed.) Humic substances in terrestrial ecosystems Elsevier Amsterdam pp.329-359 Edwards, C.A and Lofty, J.R 1977: Biology of Earthworms Chapman and Hall 333p Jackson, W.R 1993 Humic, fulvic and microbial balance: organic soil conditioning Jackson Research Center 946p Juma, N.G 1998.The pedosphere and its dynamics: a systems approach to soil science Volume Quality Color Press Inc Edmonton, Canada 315p Linderman, R G 1994 General summary In: Mycorrhizae and Plant Health F L Pfleger and R G Linderman (Eds.), APS Press, St Paul pp.1-26 Schnitzer, M 1986 The synthesis, chemical structure, reactions and functions of humic substances In: Humic substances: effect on soil and plants R.G Burns, G dell’ Agnola, S Miele, S Nardi, G Savoini, M Schnitzer, P Sequi, D Vaughan and S.A Visser (Eds.) Congress on Humic Substances March 1986, Milan Stevenson, F.J 1994 Humus Chemistry Genesis, Composition, Reactions Wiley Interscience New York 2nd Edition 512p Tan, K.H 1994 Environmental soil science Marcel Dekker Inc New York 304 p Tan, K.H and Binger, A 1986 Effect of humic acid on aluminium toxicity in corn plants Soil Science 14: 20-25 Vermeer, A.W.P 1996 Interactions between humic acid and hematite and their effects on metal ion speciation PhD Thesis Wageningen University 70 Annex - The soil ecosystem ISSN 0253-2050 Conservation agriculture Case studies in Latin America and Africa Empirical evidence has been accumulating that sustainable intensification of crop production is technically feasible and economically profitable Added benefits are the improvement of the quality of the natural resources and protection of the environment in currently unimproved or degraded areas, provided farmers participate fully in all stages of technology development and extension This has led to what is called “conservation agriculture” Three criteria, i.e no mechanical soil disturbance, permanent soil cover and crop rotations, distinguish conservation agriculture from a conventional agricultural system This publication demonstrates how conservation agriculture can increase crop production while reducing erosion and reversing soil fertility decline, thus improving rural livelihoods and restoring the environment in developing countries The document is based on testimonies and experiences of farmers and extensionists in Latin America and Africa FAO SOILS BULLETIN 78 ... FAO Zero tillage, Argentina Conservation agriculture Case studies in Latin America and Africa FAO SOILS BULLETIN 78 Land and Plant Nutrition Management Service Land and Water Development Division... conservation of the soil structure and stimulating soil biota Information on the soil ecosystem is provided in Annex 6 Introduction Conservation agriculture – case studies in Latin America and. .. firewood and grains, but generates a surplus, which generates an extra income when sold in the market Conservation agriculture – case studies in Latin America and Africa 13 PLATE Land preparation