LEARNING
Agri
Cultures
ModuLE 3
(INtERIM vERsIoN)
Cropping systems
This publication forms part of the Learning Agricultures series for educators, providing insights on sustainable small-scale agriculture. Ileia uses the
Attribution-Noncommercial-ShareAlike 3.0 Unported Creative Commons Licence. In brief, users are free to copy, distribute and transmit the contents of this module but the source must be acknowledged. The contents of this module may however not be used for commercial purposes. If you alter or translate any sections, the resulting work must only be distributed under the same or a similar license to this one. For details, please see http://creativecommons.org/licenses/ by-nc-sa/3.0.
One exception is video R4.6 which falls under copyright.
Authors: Mundie Salm, ileia
Illustrator: Fred Geven, ‘s-Hertogenbosch, the Netherlands
Language and copy-editor: Nick Parrott, TextualHealing.nl, Wageningen
design & Layout: Frivista, Amersfoort, the Netherlands
Funding: SIDA and DGIS
cover photo: Flemming Nielsen, mixed sorghum field in Central Mozambique
Acknowledgements
The author would like to acknowledge the contributions of the following people:
Frank van Steenbergen (MetaMeta) and Willem Stoop and Edith Lammerts van Bueren, members of our ‘sounding board’ for very helpful input, comments and suggestions for improvements on technical details in the first two blocks. Frank van Schoubroeck for suggestions for Learning Block 3. Nick Parrott whose clean-up of the final draft went beyond language and copy-editing. Fred Geven, our patient illustrator who made much creative input. Matilda Rizopulos who compiled the photographs and references and Maud Radema please note: This module is an interim version. We welcome comments and suggestions for improvement. Published by ileia, Amersfoort, the Netherlands
why Learning Agricultures?
Over the years, the readers of ileia’s magazines, as well as our international partner network, have asked for support material explaining the principles behind sustainable small-scale farming. With 25 years of publishing practical cases from around the world, ileia has a wealth of material for exploring this subject. The Learning AgriCultures series is our response to this request. Sustainability translates differently under specific local conditions so this series does not intend to offer solutions to all the problems. Its objective is to stimulate a culture of learning about sustainable small-scale farming. Through probing questions, and a variety of educational resources, we hope that this material helps feed into and provoke discussions and deeper reflections on the important contributions of small-scale farming, and what sustainability means in different contexts faced by students. The series is not intended as a field guide and does not focus on technical details about farming methods. It does however suggest further references for digging deeper into technical questions.
who is it for?
Learning AgriCultures is a learning resource particularly aimed at educators seeking support material for explaining about sustainable agriculture in their courses, at a university or college level, in special NGO training courses or other professional environments. Courses in which this series could be useful include agriculture, rural development, environmental studies, research & extension, agricultural policy-making. The likely target group will be students who primarily, but not exclusively, (will be) working in developing countries.
what is in it and how can it be used?
The Learning AgriCultures series has seven modules. It explores small-scale (family) farming and how it can become more sustainable. Each module has three learning blocks, looking at its theme from the perspective of: 1) the farm, 2) issues in the wider context that affect farming, and lastly 3) sustainability and governance issues. These learning blocks are followed by a section giving details of educational support materials. Here educators can find and choose from practical cases (mostly drawn from 25 years of articles in ileia’s archive), exercises, games, photos, videos, checklists for farm visits as well as further references (free books and websites) that they can use to supplement their courses. A separate glossary of difficult terms, drawings and diagrams explains concepts from throughout the series. It is hoped that the suggested questions, practical examples from around the world, and different kinds of resource material, will enable educators to make their own lesson plans, drawing on what is relevant to their own regional context and student group.
Module 1 • Sustainable small-scale farming Module 2 • Soil and water systems
Module 3 • Cropping systems Module 4 • Livestock systems
Module 5 • Labour and energy in farming
Module 6 • Markets and finance for small-scale farmers Module 7 • Knowledge for small-scale farming
Learning Agricultures: Insights from sustainable small-scale farming
Foreword to Learning
This module introduces different aspects of small-scale farmers’ cropping systems, focusing on three viewpoints - the farm, wider contextual issues and governance. Small-scale cropping systems are often mixed and highly productive, making use of interactions with other elements on the farm, such as between different crops, and with livestock. Small-scale farming is the source of valuable crop diversity in terms of species as well as varieties. It supplies many crops that would not otherwise be produced, such as those that are important to local food security and markets, such as with underutilised crops. In seeking greater sustainability in cropping systems, one general theme keeps recurring: the need to make use of, conserve and integrate greater diversity into farming systems and the wider landscape. For farmers, increasing diversity provides many advantages and opportunities, although it also presents a number of practical challenges. The advantages include greater adaptability, minimising risk and making use of interactions with different organisms and sub-systems on and around the farm. The challenges of diversity management involve the need to find a good balance between many different elements and high labour and knowledge requirements. This module describes different aspects of mixed cropping practices. It also looks at how to sustainably intensify cropping systems, through better knowledge and observance of location-specific ecological interactions. It describes
recent advances in the development of crop biotechnologies, such as genetic engineering and formal seed systems, which have had a tremendous impact on cropping practices around the world. More and more farmers have access to improved seed as part of a package of chemical inputs and better irrigation. This has increased production of many important crops. However, these developments have also meant that the genetic base for agricultural biodiversity in crop
species, varieties, as well as ecosystems, has become narrower. Technological developments and the introduction of intellectual property rights over plant varieties also bring the danger of small-scale farmers having less control over their seed systems. The importance of engaging farmers in land-use planning, crop breeding and conservation, and in implementing policies that value and support
Summary
FoREwoRd to LEARNING AGRIcuLtuREs sERIEs
3
suMMARy oF thIs ModuLE
4
GuIdE to EducAtoRs
8
Purposes of Module 3 8
How to teach Module 3 8
What is in Module 3 8
Glossary for the whole series 9
Making lesson plans from this module 10
Example of a Lesson Plan 10
LEARNING bLocK 1: cRoppING systEMs
13
oN thE FARM
1.1 Introduction
14
1.2 distinguishing aspects of crops
14
1.2.1 Crop products 15
1.2.2 Scientific classification 16
1.2.3 Reproductive strategies and genetics 17
1.3 crops as part of a system of interactions
18
1.3.1 Crop interactions with organisms in the soil 19
1.3.2 Crop interactions with other plants 20
1.3.3 Crop interactions with animals 21
1.3.4 Crops and farmers 22
1.4 Farm management and cropping systems
23
1.4.1 Farmers’ selection processes and agrobiodiversity 23
1.4.2 Using crop diversity as a buffer 25
1.5 sources for this learning block
29
LEARNING bLocK 2: cRoppING IssuEs IN
31
thE wIdER coNtEXt
2.1 Introduction
32
2.2 Landscape approach to cropping systems
32
2.2.1 Forest ecosystems and small-scale cropping 33
2.3 Access to plant genetic resources
35
2.3.1 Traditional local PGR systems 37
2.3.2 Formal PGR systems 38
2.3.3 Conservation of crop genetic diversity 41
2.4 Management of weeds, pests and diseases
42
2.4.1 The use of chemical pesticides 43
2.4.2 Integrated pest (and weed) management 44
2.5 Intensification of crop management
45
2.6 sources for this learning block
46
LEARNING bLocK 3: GovERNANcE
49
ANd sustAINAbLE cRoppING systEMs
3.1 Introduction
50
3.2 Governance issues
51
3.2.1 Involving farmers in rural planning 51
3.2.2 Intellectual property rights, crops and small-scale farmers 52 3.2.3 Including farmers in formal research, breeding 54
and conservation programmes
3.3 policies supporting sustainable cropping systems
55
3.3.1 Research and development priorities 55
3.3.2 Regulations on inputs: hazardous pesticides and GM organisms 55 3.3.3 Protecting farmer-centred local PGR systems 56
3.3.4 Pricing policies 57
3.4 sources for this learning block
57
EducAtIoNAL REsouRcEs FoR ModuLE 3
59
R1. Exercises and Games
60
R1.1 Planning a field layout for mixed cropping 60 R1.2 Realising the value of underutilised crops 61
R1.3 Role play on insecticide resistance 62
R1.4 Reforestation and policy measures 64
R2 Articles about practical experiences
66
R2.1 Are polycultures always more sustainable? 66
R2.2 Crop rotation 66
R2.3 Agroforestry (4 articles) 67
R2.4 Home gardens 68
R2.5 Underutilised crops (2 articles) 69
R2.6 Cropping systems and forest ecosystems (3 articles) 69
R2.7 Local PGR systems: Seed fairs 71
R2.8 Formal seed systems: Genetically modified organisms 71 R2.9 Local PGR systems: Community seed banks (2 articles) 72
R2.10 Pesticide use and beneficial insects 72
R2.11 Different view on weeds 73
R2.12 Integrated pest (and weed) management (3 articles) 73 R2.13 Sustainable intensification practices (2 articles) 74 R2.14 Governance issues: Protecting the sustainable of ecosystems 75 R2.15 Governance issues: Participatory plant breeding 76
R3. photo gallery
77
R4. videos
80
R4.1 Agroforesty: A sustainable tropical island land use system 80 R4.2 Dalit food systems: a new discourse in food and farming 80
R4.3 Nature Farmer 81
R4.4 Bt Cotton in Andhra Pradesh: a three year fraud 81
R4.5 Biotech pear is a singular tree 82
R4.6 The Transcontainer Project – GM crop containment in the EU 82
R5. Farmer visit and field exercises
84
R5.1 Farmer interview checklist 84
R5.2 Field observations 85
R6. Further references for Module 3
86
R6.1 Books and field guides 86
R6.2 Interesting websites 88
Appendix
95
R2 Articles 96
Guide to educators
puRposEs oF ModuLE 3
Figure 1: Educators, the target group of Learning AgriCultures
For educators:
• to learn about a systems approach to teaching about sustainable crop production as part of small-scale farming systems.
For students:
• to understand about crop production dynamics in small-scale farming; • to learn about how to make cropping practices in small-scale farming more
sustainable - and how to support the efforts of small farmers.
how to teach Module 3
About 16 contact hours will be needed to teach this entire module. This does not include time for conducting interviews with farmers, or the time that students will spend on assignments. Educators will need to decide for themselves whether to use the entire module or parts of it when making their lesson plans.
At the end of this section, an example is given of how to make a lesson plan from the material included in this module. The total time required and duration of each lesson will vary depending on the level of the students, the knowledge of the educator and how many games and assignments you choose to include in the course. A very important component of the module is to visit and interview at least one farmer – so that students can better understand the practical realities of farming systems in their area.
what is in Module 3?
This module is the third one in the Learning AgriCultures series. As with the other modules, it includes three learning blocks with theoretical information and a section with support material as Educational Resources. Specifically, the content of this module is as follows:
LEARNING bLocK 1:
cropping systems on the farm
This block provides an overview of different kinds of interactions crops have with organisms in the soil, other plants (including trees), predatory and beneficial animals, and farmers. Farmers’ management practices are introduced, together with the concept of agrobiodiversity and different ways crop diversity can become a buffer on the farm.
LEARNING bLocK 2:
cropping issues in the wider context
Four issues are analysed that have a great impact on cropping systems around the world: activities affecting crops at a landscape or ecosystem level, access to seed and other plant genetic resources, the management of weeds, pests and disease and the sustainable intensification of cropping practices.
LEARNING bLocK 3:
toward more sustainable cropping systems
This block describes how governance influences small-scale cropping systems and focuses on three major issues: including farmers in wider land-use planning, intellectual property rights and participatory plant breeding. The module concludes with examples of policies that enable and support sustainable small-scale cropping systems.EducAtIoNAL REsouRcEs:
Different kinds of support material are provided for educators to stimulate deeper insights and discussions in class or as assignments. Throughout the main texts, boxes suggest links to resources (see the list below) and to probing questions that are indicated by the symbols found in Figures 2 and 3.
• Exercises and games: for in-class and as assignments, to help deepen understanding of cropping systems.
• Cases: suggestions for further reading and assignments based on articles from ileia’s magazine archive, to expose students to different practical examples of methods farmers use and to stimulate discussion.
• Photographs: for in-class, these can help start discussions with students on the practical implications of different issues raised in the module.
• Videos: for in-class, to complement the teachings with visual examples from around the world.
• Farmer interview(s): suggested visit with small-scale farmers, checklist and further on-farm exercises for students.
• Further references: suggestions for freely available books and interesting websites.
Glossary for the whole series
This is separate from the module and includes definitions for difficult terms for the whole Learning AgriCultures series.
Figure 2: symbol to indicate link to suggested questions
Figure 3: symbol to indicate link to educational resources
Three basic questions need to be asked when preparing a lesson plan: • What do you want your students to learn?
• How are they going to learn it?
• How will you know if they have learned it?
A lesson plan therefore needs to reflect these questions by setting out the learning objectives, aims, or goals of the unit, and how it relates to the whole course. The lesson plan should also include a list of the materials needed and the learning aids and references that you will use. See the example on the next page:
Example of a Lesson plan
Lesson The implications of mixing crops in small-scale farmingTime 3 hours
Objectives After completion of this session participants are able to:
• demonstrate an understanding of these concepts: crop agrobiodiversity, polycropping, monocropping, complementarity, synergy, multi-purpose functions and recycling • Recognise different methods of multiple cropping
• Realise some of the practical benefits and limitations of mixed cropping practices in small-scale farming.
Prerequisite Introduction to cropping systems’ ecological interactions
Time Content Teaching method Teaching aid
15 min
Central question: What is
agrobiodiversity and how does it relate to crops?
Introduction: agrobiodiversity
and link with the last session on cropping systems and ecological interactions.
Plenary discussion:
Ask students what they understand by agrobiodiversity
Blackboard, chalk
Elaborate on definition from FAO (Box 3)
Time Content Teaching method Teaching aid 45 Central question: How can different
kinds of crops grow together and be productive?
Important points:
• Crops’ ecological interrelationships • What do we mean by polycultures and
monocultures?
• Define concepts of complementarity, synergy, multi-purpose functions and recycling
• Distinguish between simultaneous and sequential mixes
Introduction: mixed cropping Plenary discussion:
• What are the different ways that crops can compete for and share light, space, nutrients and water?
• Compare interactions in monocultures and polycultures (build on previous lesson about ecological interactions)
Blackboard, chalk Use Figure 7 (Crops as part of wider system) Option: Article R2.1 In defence of monocultures 10 BREAK
80 Central question: What different ways are
there for mixing crops?
Important points: • Crop rotation • Multi-cropping • Agroforestry • Home gardens • Underutilised crops • Diversity at edges Brainstorm:
• What could be potential benefits and limitations of mixing crops when thinking of interactions?
• What about for social or economic factors e.g. labour demands, marketing, food security, nutrition?
Watch a video e.g. on agroforestry in
Guam. Discuss the questions it raises and how they relate to your region
Blackboard, chalk Video R4.1 (21 minutes): Agroforestry in Guam Computer, beamer 10 Concluding remarks about small-scale
farming and multiple cropping practices
Wrap up and explain group exercise. Respond to questions.
20 Central question: Based on the lesson,
can students make a mixed cropping design?
Exercise in small groups: Design a farm’s cropping system based on 10-15 crops (start the exercise in class, but complete as homework)
1
LEARNING bLocK
Mohanty Adivasi woman harvesting millet in India, photo from ORRISSAA
How do small-scale farmers around the world
manage crops (including trees) in order to get
productive livelihoods? In what ways do crops
interact with different systems on the farm? What are
the different roles that crops play in the farm and how
do they contribute to livelihoods? What do we mean
by agrobiodiversity? What do we need to consider
in order to increase the agrobiodiversity of cropping
systems? What different practices do farmers use to
maintain diversity in their farms?
Cropping systems on the
farm
The cultivation of crops on arable land is the very foundation of agriculture. How crops are cultivated varies in countless ways around the world, depending on many factors such as the climate and weather patterns, the resource base, soil and water constraints, and the knowledge and access rights of the farmers. Cropping systems vary from extensive and mobile systems such as shifting cultivation, to mixed systems that integrate many elements in the farm, to highly intensive industrial farming, in which large stands of single crops are grown continuously. All of these cropping systems are practised in tropical climates, although in semi-arid and semi-arid environments rainfall (and access to irrigation) limits the timing and extent of agriculture. In (sub) tropical climates mixed cropping, which includes perennial crops and agroforestry (crops together with trees), predominate. In more temperate parts of the world, arable farming is more often based on highly productive and modern input-intensive annual crops, such as cereals.
Regardless of where they are, farmers aim to balance the different ecological needs of the crops that grow in their environment, so as to develop strategies to make their farms more productive. This learning block sets the stage by first describing distinguishing aspects of crops, followed by a look at different ecological interactions between crops and other organisms and processes at the level of the farm. It then focuses on small-scale farmers’ crop management practices, and how a diversity-based approach based on multiple cropping can enhance the sustainable productivity of their systems.
1.1 Introduction
1.2 distinguishing aspects of crops
It is very difficult to make generalisations about crops because of their extreme diversity. They not only look different, offering hugely diverse products from different parts (leaves, roots, tubers, stems, flowers, etc.), with different properties: from foods, medicines, fodder, fibres, fuels, wood, and so on. They also provide a variety of services: the release of oxygen, habitats for beneficial predators, root networks that give stability and structure to the soil and help water permeation. Some crops fix nitrogen or draw nutrients from deep in the soil. Trees and bushes can provide wind breaks, protection from grazing cattle and shelter from the sun. Plants add vitality to even the most barren places, and farmers’ cropping systems play a role in shaping landscapes around the world. This section provides an overview of the importance of crops from different vantage points - classification in terms of main products, scientific classes, and according to reproductive strategies and genetics.
What is (are) the staple crop(s) in your area? Do these crops fullfill other functions as well? What other types of products do small-scale farmers grow
1.2.1 Crop products
The UN’s Food and Agriculture Organization (FAO) has developed a simple classification system for crops according to the main product type and whether they are a “temporary” or “permanent” (i.e. perennial) crop (see Sub-section 1.2.3). FAO (2010) now classifies all crops according to nine types, as follows: • Cereals: The main cereal crops are (in order of hectares planted globally) wheat, rice, maize, barley, oats, rye and sorghum. Cereal crops or grains are used for food, feed for livestock and in industrial processes producing items such as alcohols and oils. Cereal grains are considered to be “staple crops;” they are grown in greater quantities and provide more calorific energy than any other type of crop. Over half of the global requirement for proteins and calories is met by just three cereals: maize, wheat and rice. There are also many other cereals that are locally extremely important for food security, such as fonio in West and Central Africa, quinoa (technically a “pseudo cereal”) in Latin America and teff in Ethiopia (all from Bioversity, 2010).
• Vegetables and melons: These are further subdivided into leafy or stem vegetables (e.g. cabbages and artichokes); fruit-bearing vegetables (e.g. cucumbers and pumpkins), root, bulb or tuberous vegetables (e.g. carrots and onions); and mushrooms.
• Fruit and nuts: These are further subdivided into (sub) tropical fruits (e.g. bananas, mangoes and avocadoes) and citrus fruits; grapes; berries; pome and stone fruits (e.g. apples, apricots); nuts and “others”. Plantain is included here, although it is an important staple crop in some African and Caribbean countries.
• Oilseed crops: soyabeans; groundnuts; other temporary oilseed crops (e.g. castor bean, sesame); permanent oilseed crops (coconuts, oil palms).
• Root/tuber crops with high starch or inulin content: These differ from those classified as vegetables because of their starch/inulin content. These are also considered to be staple crops. This category includes potatoes; sweet potatoes; cassava; yams and others.
• beverage and spice crops: beverage crops are permanent crops such as coffee, cocoa and maté; spice crops include temporary (e.g. chillies and peppers) and permanent crops (e.g. cinnamon, vanilla and ginger). • Leguminous crops: these include beans, peas and lentils etc. Legumes
provide the important service of enhancing the availability of nitrogen in the soil. This is elaborated upon in the next section.
• Sugar crops: examples include sugar beet, sugar cane and sweet sorghum. • Other crops: including grasses and fodder crops; fibre crops, medicinal,
aromatic, pesticidal crops; rubber; flower crops; tobacco; and others.
It is important to remember that many crops have multiple purposes, which are not reflected in this classification, as they are classified according to their main commercial use. For example, soyabeans are categorised under oilseeds because this is the principle product; although they are also leguminous and as such can provide an important service to soil fertility. Another example is cotton, which is categorised as a fibre crop, but which also produces oil as well as contributing to
1.2.2 Scientific classification
While FAO bases its system on crop-product types, scientists and farmers around the world have long found different ways to classify plants according to common ecological characteristics and appearance. As more is learnt about genetic variability (see next section), scientific classification systems of all organisms will change because they show more clearly whether organisms are (closely) related or not, according to how similar their gene sequences are. Four different classes are introduced here, as they will be referred to the most in this module: “family”, “genus”, “species” and “variety”.
• Family: this is a group of plants that has many common botanical features that are often easy to recognise. The characteristics of different families can be important for sustainability and can be used as the basis for farmers’ strategies in combining crops through inter-cropping (planting different types of crops in the same bed or field) or crop rotation (rotating different crops in the same bed or the same field over time). A very important family of plants for farmers is the Leguminosae (or legume) family. These plants form symbiotic relationships with rhizobia, which belong to the family of bacteria called Rhizobiaceae. When legumes (e.g. beans, peas, soyabeans, groundnuts, lentils, alfalfa, clover, or trees such as Leucaena or Gliricidia, etc.) are planted in inter-crops, green manures or in crop rotation, the rhizobia make nitrogen from the air directly available to other plants.
• Genus: This is the “generic” or common name given to a specific group of plants within a family – e.g. Brassica is one of the genera within the family of Brassicaceae or Cruciferae. (The members of this genus are collectively known as cabbages).
• Species: This is the more “specific” name of a group of plants within a genus. Together, the genus and species name define one particular plant (with the whole name italicised, the genus capitalised, and the species in lower case – e.g. Leucaena leucocephala). For example, the family of Brassicaceae contains What are examples of legumes
in your area? Do farmers plant them in combination with other crops to benefit crop interactions?
Approximately 16 500 species of legumes exist, though not all are able to form an association with nitrogen-fixing bacteria. Rhizobia are single-celled bacteria, approximately one thousandth of a millimetre in length. These bacteria form a mutually beneficial association, or symbiosis, with legume plants. The rhizobia enter into the roots of legume plants which respond by producing a round and visible structure called a root nodule. Taking nitrogen from the air the rhizobia then convert the nitrogen into a form that plants can use, called ammonium. This is known as “nitrogen fixation”. Most plants need specific kinds of rhizobia to form nodules. For example, the rhizo-bia that form nodules on soyabeans cannot form nodules on clover. For nodulation to take place the right plant-rhizobia combination needs to be present. It also requires a healthy soil environment that is not too acid (i.e. has a low pH), or suffer from aluminium toxicity, nutrient deficiencies, salinity, water-logging or the presence of root parasites, such as nematodes. Sometimes it is necessary to inoculate legumes with the correct rhizobia to ensure that nitrogen-fixation will take place.
well-known species such as Brassica oleracea (cabbage, cauliflower, etc.),
Brassica rapa (turnip, Chinese cabbage, etc.), Brassica napus (rapeseed, etc.), Raphanus sativus (common radish), etc.
• Variety: Within species, there can further be different varieties or “cultivars” (i.e., cultivated varieties) containing different traits in terms of adaptation to different conditions such as dryness, soil acidity, pest and disease resistance, but also in plant height, maturity cycle, etc.
more likely to have a combination of desired traits.
In recent times, the study of genetics has led to a greater understanding of genes and how specific traits are passed from generation to generation of all living organisms. For example, children usually look like their parents because they have inherited their parents’ genes. Genes are units of heredity in a living organism and consist of a long molecule called DNA, which is copied and inherited across generations. DNA is made of simple units that line up in a particular sequence within this large molecule. The order of these units carries genetic information, a set of “instructions” for how each living organism develops and operates.
“Plant genetic resources” (PGR) is a term used to refer to seeds and planting material of all varieties – traditional, modern cultivars, wild relatives of crops and other wild plant species (PGR systems will be discussed further in Section 2.3). The term “genetic variability” describes how different plant characteristics are represented in different varieties within one species, or even within one variety. Genetic variability in a population is important for biodiversity, to enable a population to adapt to varying environmental conditions (e.g. soil, climate, etc.). The diversity within crop species is at least as important as diversity between species. We will discuss biodiversity further in Section 1.4.
1.3 crops as part of a system of interactions
To understand issues of sustainability and small-scale farming it is helpful to look at crops as being part of a wider system of interactions with different kinds of organisms. Crops interact with other plants and organisms in several ways that critically determine how they grow. In a balanced cropping system, the positive interactions (i.e. those that help the crop grow well) are strengthened, and the negative interactions are minimised through management practices. Understanding these different kinds of interactions is important in understanding the sustainability of crop production. Figure 7 presents a model of some of the major interactions between crops and their wider environment. Two crops, maize and beans are used as an example, but the different kinds of elements that interact with crops form a general pattern. This model provides a simplified view and does not show for example, the negative interactions of trees, other crops, weeds and (soil-borne) pathogens. The rest of this section reflects on ways in which crops interact with different elements and sub-systems that can promote or detract from their growth.
Figure 6: A dNA molecule is composed of simple units lined up in a sequence that looks like a long coil.
1.3.1 Crop interactions with organisms in
the soil
Module 2 focused on the importance of the soil and water system; this section examines interactions between crops and the soil system. Several factors drive interactions within the soil: soil structure, the availability of nutrients and
moisture, space and interactions with the root system of the crop and the activities of the soil’s micro-organisms. These all have an important influence on crop growth. Soil systems include nutrient cycling through plants. Nutrients come from a variety of sources and their availability depends on a number of favourable conditions. Even if desired nutrients exist in the soil, they may not be accessible to the crops, for example they may be physically out of reach of the roots. Moreover, they need to be chemically available: nutrients need to be mineralised (oxidised) and be in solution (i.e. mixed with water) in order for plant roots to be able to take them up. Also, the soil’s pH must be neither too alkaline nor too acid.
Figure 7: crops as part of a wider system of ecological interactions that need to be kept in balance through farmers’ practices.
Root systems are composed of long thick roots, that provide structural support, and shorter, fine roots that are important in the uptake of nutrients and water. A good soil structure allows roots to penetrate and spread in the soil. Plant roots provide a special, highly energised habitat for micro-organisms living in the area around them, called the “rhizosphere”. The activities of different organisms in the soil greatly aid the process of nutrient uptake by plants, as explained below. The soil is home to a tremendous number of micro-organisms that make up a special system, known as the “soil food web”. The vast majority of organisms living in the rhizosphere are “decomposers” that feed on root-derived compounds and organic matter in the soil. In most cases, their presence is highly beneficial to plant growth, particularly when their activities release mineral nutrients that plants can subsequently take up. Also, some organisms, such as nitrogen-fixing rhizobial bacteria (see Box 1) and mycorrhizal fungi (see Box 2), form associations with plants that allow them to get access to more nutrients. Both the micro-organisms and the plants benefit from this association (microbes get energy and carbon from the plant while plants get greater access to nutrients and increase their water uptake). These are known as mutualistic or symbiotic associations. But the soil food web also includes pests that can harm the productivity of plants, including below-ground herbivores, plant-parasitic nematodes and pathogenic fungi that feed directly on living root tissues. In a “normal” situation, the micro-organisms are in delicate balance with one another. If the equilibrium is disturbed, a specific organism may multiply excessively and become a pest problem.
1.3.2 Crop interactions with other plants
The interactions of crops with other plants, that include weeds, other crops and trees is largely based on competition for light, nutrients, water and space. However, there are also many cases in which plants complement one another’s growth, through differences in tolerance to light levels, having different root depth and, some specific cases where crop growth is enhanced by interactionsFigure 8: Micro-organisms form part of a “soil food web” which influences plant growth in both positive and negative ways.
One of the most common mutualistic associations that plants form with soil microbes is with mycorrhizal fungi. These improve access to limited nutrients, improve soil properties and the plant’s capacity to absorb water. The most important of the seven known types of mycorrhizal fungi is arbuscular mycorrhiza (AM) which influences over 80 percent of known plant species. How does it work? The AM penetrates roots, forms arbuscules, coils or vesicles in the roots that allow for hyphae (hair-like structures) to form. These hyphae have a smaller diameter than roots, can reach a greater surface area and are able to reach into the soil, transferring nutrients and water to the plant roots very efficiently. In this way, the hyphae access nutrients that the plant normally cannot, including less mobile pools of phosphorus, the lack of which is often a very important constraint on plant growth. Furthermore, greater access to phosphorus (and other limited nutrients such as copper, calcium and zinc) stimulates nodulation and nitrogen fixation by other microbes such as rhizobia (see Box 1 above).
fixed by the root nodules in beans, a leguminous crop.
Different crops have different rooting structures that can compete with, or complement, each other in accessing nutrients and moisture from the soil. The spacing of individual plants ensuring that they develop strong root systems able to withstand the invasion of weeds are a critical part of planting. Plants are either deep-rooting or shallow-rooting, which means that they access nutrients and water from different layers of the soil.
Some plants produce toxic substances from their roots that inhibit growth of other plants, even to the point of making it impossible for some other plants to become established. This is known as “allelopathy”. For example, root parasite weeds such as witch wood (Striga spp) in cereals and legumes, and broomrape (Orobanche) in crops such as vegetables and sunflowers, cause great problems for farmers in areas with low soil fertility and low annual rainfall. Other examples include black walnut trees that inhibit the growth of vegetables such as tomatoes, peas and potatoes. The mechanisms behind these allelopathic associations are still not fully understood, although they do cause great harm.
sunlight and shade
In general, crops need sunlight to be productive. Plants are primary producers and are able to capture their energy needs from the sun in their leaves and send it to their roots. Competition for sunlight is an important interaction between different plants. Little sunlight means that less energy is available, limiting the growth of crops. While water can be a limiting factor to growth and survival in dry and sunny environments, energy (in the form of sunlight) is usually the limiting factor in shady environments.
Some plants, such as those in a forest’s under-story, have adapted to very low light levels. They are known as “shade tolerant” and are highly efficient energy-users. Examples include cocoa and coffee. In general, these plants grow broader, thinner leaves, to catch more sunlight. Shade tolerant plants are also usually adapted to make better use of soil nutrients than shade intolerant plants. As shown in Figure 9, shade trees can also provide services such as accessing nutrients from deeper layers of the soil (and depositing them on the surface through leaf-fall). Trees can also benefit from the soil cover provided by low-lying plants which increase levels of soil moisture and organic matter.
1.3.3 Crop interactions with animals
The term “animals” here includes domestic livestock as well as wild mammals, birds, and insects and other invertebrates. The browsing activities of different kinds of animals influence the growth of crops and these interactions can be beneficial or detrimental. Examples of harmful interactions are larger animals such as birds, rodents or ungulates feeding on plants – whether the leaves, stems,
Figure 9: plants have different root depths, that access water and nutrients from different places in the soil.
Can you think of different kinds of weeds that are problematic in your area? Why have they become a problem, and what are farmers doing about it?
Figure 10: understanding differing light needs helps farmers plan the best relative positioning of crops.
considered to be pests, getting to the harvest before the farmers, causing disease or killing the plant.
Examples of interactions that are beneficial for crops are the activities of pollinators, the addition of nutrients to the soil through faecal deposits (or as manure) as well as the feeding habits of the predators of pests that feed on plants. As indicated in Sub-section 1.2.3, pollination - which involves the transfer of pollen between plants for fertilisation - is an essential part of plant reproduction. The activities of pollinators are clearly important for most plants. Approximately 80 percent of all flowering plant species are adapted for pollination by animals and insects. Pollinators include insects such as bees (over 25 000 bee species identified), wasps, ants, beetles, moths and butterflies, as well as vertebrates such as birds, bats, squirrels and some primates. Many other plants that do not need pollinators are pollinated by the wind (e.g. grasses, coniferous, and many deciduous, trees).
Animals that prey on browsers of crops are also known as “natural enemies”, and they help farmers to control pests and disease. Their role will be discussed more under Integrated Pest Management (IPM) in Learning Block 2. In some cases, animals are also important to safeguard the growth of vegetation. For example grass lands and heaths require regular grazing to stop the succession of larger woody plants.
1.3.4 Crops and farmers
The activities and management practices of farmers (and in some cases other people, such as herders, hunters and gatherers) strongly influence the growth of their crops. The choices they make, and how well they manage the many interactions described above, are fundamental to the productivity of their cropping systems. They need to constantly adapt their practices to nurture the beneficial interactions while minimising problems from competition and destruction by pests. In the next section, we look more deeply at how farming practices affect the growth and development of cropping systems.
What are examples of
pollinators and other beneficial animals, as well as of animals that cause problems in the main crops in your area?
This section examines the management of small-scale cropping systems: cropping patterns involve polycultures (multiple crops in the same space), monocultures (large stands of single crops), agroforestry (trees integrated into cropping systems), as well as combinations of crops with livestock, with forest systems, aquaculture, rangelands, pastures and fallow lands. Farmers have developed diverse cropping patterns and thousands of different crop varieties and animal breeds during the 12 000 years that agriculture has existed (FAO, 2010). This section gives particular attention to the dynamics of multiple cropping.
Small-scale farmers generally engage in mixed systems including multiple cropping to meet their food and livelihood needs. In developing their farm systems, farmers continuously adapt their practices in order to enhance the growth of their crops. They make the most of local conditions, adapting practices to maintain or enhance soil fertility and moisture and to protect crops against pests, disease and other harmful effects. Module 2 discussed farming practices that improve soil fertility and water processes, such as improving the quality (and quantity) of the soil’s organic matter. The management practices discussed in that module are essential for good crop growth and provide an essential background to the cropping practices discussed here.
Two major management issues for farmers are dealing with the persistence of weeds and with pests and disease. Weeds can compete with crops for space, nutrients, water and light; and if not managed properly, can greatly interfere with the productivity of cropping systems and pasture land. Some crops have greater resistance to weed interference, especially those that are larger and faster growing. It is important to understand the growth patterns of both crops and weeds in order to time when to prepare beds, sow crops and remove weeds, to give their crops a head start before weeds establish strong root systems, grow tall and start flowering. Keeping ahead of pests and pathogens before they become a major problem for their crops is also crucial. There are many similarities between pest and weed problems and the measures used to control them - from clearing practices, to removing weeds or pests mechanically, through indirect measures, or through applying herbicides and pesticides. Learning Block 2 discusses these and other practices in greater detail in a section on integrated pest (and weed) management.
1.4.1 Farmers’ selection processes and
agrobiodiversity
Small-scale farmers’ selection processes lead to crop (and animal) varieties that are well adapted to the location-specific conditions of their farm (see “landraces”
1.4 Farm management and cropping systems
Figure 11: Farmers’ practices favour the growth and development of certain crops, while seeking to minimise the effects of weeds, pests and diseases.
example, favour seeds from plant varieties that have proven to be tolerant to drought conditions and/or resistant to particular pests and diseases. Or they might select according to fruit size, shape or colour, plant height, early or late-maturing varieties, or because of a special taste or cooking characteristics, according to local traditions.
Farmers’ selection, seed-saving and exchange activities have allowed them to develop tremendous genetic diversity in local landraces over the millennia. A key characteristic of landraces is that genetic diversity is maintained, through natural processes (e.g. open-pollination), seed selection and adaptation processes. When fields are planted close together, there is a constant gene flow between landraces. This diversity allows for natural protection against pests and diseases and buffers against environmental fluctuations. In this way, small-scale farming systems aim for harvest security and sustainability of production over time.
These selection activities have not only produced great diversity in crop varieties, but have also built up detailed knowledge about “agrobiodiversity” (see Box 3) which goes beyond on-farm crops and includes many plants, animals and micro-organisms in their farms’ specific ecological conditions, how they can be actively conserved and used sustainably. In general, women and men farmers have different priorities and knowledge about their cropping systems. Especially in traditional societies, a major priority for women is food and in particular the food security of their families. Women therefore have specific, traditional knowledge of seeds, harvesting and storage techniques for food crops. Men in these societies tend to be more concerned with cash crops, grown to meet household expenses. Their knowledge is therefore often focused on how agrobiodiversity and farming practices relate to cash crops. In many places, however, these roles are shifting and becoming less clearly defined, as family members are increasingly getting involved in off-farm and migrant employment to earn additional cash.
Despite ongoing development of crop diversity by farmers, overall crop genetic diversity has become increasingly narrower throughout the world over the last sixty years. The FAO estimates that of the 250 000 to 300 000 known edible plant varieties available to agriculture, about 7 000 (or less than 3 percent) are currently used by people. Today, 75 percent of the world’s food is generated from only twelve crop and five animal species. Three crops – rice, maize and wheat – contribute nearly 60 percent of plant-based calories and proteins Is it clear in your region that
men and women have different kinds of knowledge about (different) crops? How are gender roles divided regarding cropping systems on farms in your region?
Agricultural diversity (or agrobiodiversity) is the variety and variability of animals, plants and micro-organisms that are used directly or indirectly for food and agriculture, including crops, livestock, forestry and fisheries. It comprises the diversity of genetic resources (varieties, breeds) and species used for food, fodder, fibre, fuel and pharmaceuticals. It also includes the diversity of non-harvested species that support production (soil micro-organisms, predators, pollinators), and those in the wider environment that support agro-ecosystems (agricultural, pastoral, forest and aquatic) as well as the diversity of the agro-ecosystems themselves (Definition from FAO, 1999)
has led to tremendous positive benefits – in particular higher food production to meet the needs of a growing population. Yet, it has also caused losses in agrobiodiversity as multiple “traditional” or local varieties are being replaced with few, improved, varieties that are grown over large areas. Along with the losses in agrobiodiversity, farmers’ knowledge about specific local crops, and their selection and management practices disappear. Modern technological developments have had a great impact on farmers’ seed-saving practices. Learning Block 2 goes more deeply into the issue of farmers’ access to seed and other planting materials, and how agricultural diversity has been affected by this.
Looking at the interrelationships between crops and other organisms (see Figure 7 above), it becomes clear that losses in crop varieties can also affect many other organisms. The importance of pollinators in plant reproduction was discussed above. Pollinators also need a variety of plants to be able to feed well. Some plant species rely on a particular set of pollinators to provide pollination services. Pollinators have suffered pressure on their habitats because of activities such as land clearing for agricultural purposes, pesticide use, tourism and the introduction of exotic species. All of these losses have had tremendous impacts on the sustainability of cropping systems. The next section discusses cropping systems that are based on building up biodiversity and improving sustainability.
1.4.2 Using crop diversity as a buffer
Diversity typifies small-scale farming, where farmers depend on several crops as well as mixed systems to meet their food and livelihood needs. Through their practices, farmers seek a balance between favourable conditions of fertility, water and light, while also keeping weeds and pests under control. When managed carefully, having a mix of crops offers a number of advantages. It can offer a kind of buffer to farmers by spreading risks in case of crop failure, unpredictable weather, falling market prices, etc. It also gives farmers more room to adapt to changes. Systems based on diversity can provide more options for recycling nutrients and better regulation of soil moisture processes. However it does take great effort to learn how to manage these mixed systems.
Small-scale multiple cropping systems tend to have higher productivity in terms of harvestable products per unit of land area and of energy use than large-scale intensive monoculture systems, though the productivity of each crop itself may be lower than when grown as a sole crop. When planned well, mixed systems can regulate undesirable organisms such as pests, weeds and pathogens. For example, planting cover crops and well timed inter-crops can suppress weeds; and providing nectar-producing plants and alternate “hosts” (such as specific weeds) in and around fields can lead to the build-up of predator populations and increase the biological control of pests. Nevertheless, systems with a mix of crops are more complex and require more careful management. Patience is needed for trial and error and careful observation to be able to adapt knowledge and skills
Figure 12: Losses in crop species and varieties can affect the survival of many other organisms such as pollinators, particularly if they are specialists rather than generalists.
Do you know about crop diversity in your region? Are farmers growing improved varieties? If yes, how do they use them? Are local varieties being replaced?
Go to R2.1 to discuss an article that asks the challenging question of whether
polycultures are always more sustainable than monocultures.
timing and sequence of crops.
Mixed cropping systems require planning, in terms of time and space. For this, a good understanding of the crops’ needs is necessary: i.e. planting date, rotation and timing of fertilisation and optimal plant densities and spatial arrangements. In managing polycultures, farmers also need to understand relationships of complementarity and synergy, multi-purpose functions and recycling within their whole farm.
• Complementarity: describes how different elements in the system help others to grow better (e.g. when one crop provides protection against pests, or increases the availability of nutrients, for another crop - these can be planted close together to enhance the beneficial elements).
• Synergy: when elements co-operate and build on each other, thus increasing the farm’s output, (e.g. crops with different root depths growing in the same place; combining an early maturing crop with a late maturing one, for example maize with pearl millet in West Africa).
• Multi-purpose functions: describes how a single element in the system may perform several different functions (e.g. a tree providing different products such as food, fibre, nuts, medicines, etc.), shade, live fencing, leaves for fodder, etc.). • Recycling: when the end-product of one system becomes an input and
resource for another (e.g. manure from livestock becoming a nutrient resource for crops; crop residues being used for mulching to replenish nutrients, or for fodder for livestock).
A number of practices can be used to build up the kind of biodiversity that will help promote more sustainable ecological functioning on the farm. Some of the practices mentioned in Module 2 not only build up organic matter but also help increase the diversity in a farm’s cropping system: mixing crops and crop varieties over space and time through cover crops and green manures, intercrops and crop rotation. Besides the ecological benefits that this diversity can bring to the farm, it also brings dietary benefits – through providing multiple food sources. It can serve as a buffer against economic risks, giving more options for selling or exchanging products in the marketplace. The following paragraphs provide short descriptions of different cropping practices that farmers use to increase biodiversity and enhance the sustainability of their farms.
crop rotation
This practice involves growing a sequence of different crops over time on the same plot. The logic of crop rotation is to build up synergies and
complementarities through cropping sequences. By rotating crops farmers avoid a build-up of pathogens, pests, and weeds, that often occurs when a single species (or crops from the same family) is continuously cropped. For this reason crops that are directly related should not be planted in the same bed for about three seasons. Another strategy is to alternate deep-rooted and shallow-rooted plants to improve the soil structure and to utilise nutrients at different levels in the soil. Rotation also improves the efficiency of nutrient use, avoiding excessive depletion See R2.2 for an article from
Zambia where farmers have modified the “Mambwe mound” shifting cultivation systems by introducing a cereal-legume crop rotation together with mulching on mounds.
fertility demands and contributions (e.g. replenishing nitrogen by planting leguminous crops prior to and following nitrogen-hungry crops such as cereals). For example, in Zambia, a traditional shifting cultivation system was improved and intensified through use of compost and cereal-legume rotation on mounds.
Multi-cropping
This set of practices mixes two or more crops in the same space (horizontally or vertically) during a single season. In this way, large stands of single crops, or monocultures, are avoided. Multi-cropping practices include:
• Inter-cropping or companion planting: planting of different crops close together at the same time and in the same bed; also the integration of trees with crops (see agroforestry below).
• Double-cropping: a second crop is planted after the first has been harvested. • Relay cropping: a second crop is started amidst the first crop before it has
been harvested.
• Cover cropping: growing an additional low-lying crop for the purposes of keeping the ground covered to: avoid soil erosion; increase soil fertility (usually through the use of “green manures” which are in most cases legumes that fix nitrogen) and control weeds. The selection of the type of a cover crop also includes considerations of whether the crop provides food, fodder or a cash crop. The principles for these different types of multi-cropping are the same:
integrating different crops that allow for complementary synergies in nutrient uptake, attracting natural enemies, buffering against or even repelling pests or weeds, while avoiding competition for nutrients, water and light that harms the productivity of, at least, the main crop. It takes some experimentation to find the right combinations, and to be sure that productivity is not lost due to competition.
Agroforestry
This involves combining arable crops with trees. It is also sometimes referred to as agro-silviculture or multi-storey cropping. Agroforestry has long been a normal practice of small-scale farmers, particularly in the humid tropics. When managed well, trees offer many services that can be advantageous for cropping systems; however as seen in the previous section, it is important to take care that the addition of trees do not cause harm to crops because of competition for water and nutrients and that crops do not become shaded out. The following issues should be considered in relation to trees.
The deep-rooting system of trees can help prevent erosion and allow trees to tap into water and nutrients that are unattainable to annual crops. Yet before combining woody perennials with crops the relationships between rooting structures need to be well understood. For example, where there is low rainfall, trees may develop horizontal roots to reach rain water and can present unwanted competition for water and nutrients in semi-arid areas. Also, care must be taken that there are no toxic elements in the trees’ foliage or roots that may inhibit
Go to R1.1 to design a farm’s cropping system based on food crops, staple crops, underutilised crops, market crops and trees. Think about examples of complementarity, synergy, multi-functionality and recycling.
Go to video R4.3 to hear a small-scale farmer in Sri Lanka’s views on mixed farming.
Figure 13: Agroforestry
combines both crops and trees in one system.
Adding leguminous trees and bushes is advantageous as they can fix nitrogen that annual crops can benefit from. Trees improve the micro-climate by moderating ground temperatures, moisture levels, providing shade and windbreaks. Nevertheless, it is important to understand the light needs of lower crops and be sure they can still grow well under a canopy. Trees offer a wide variety of products: wood for fuel and building purposes, food, fibre, natural pesticides or medicines, fruit, nuts, oils, nectar, dyes, gums, waxes, resins, as holders of hives for honey production, etc. as well as production of fodder for livestock or fish. Being perennial, trees require little labour. On the other hand, trees are a long-term investment, and most of these products cannot be harvested until a number of seasons have passed. Because of the time involved in growing woody perennials, farmers usually need to have secure access to land tenure before they are willing to make such an investment. Another constraint to consider is that trees can affect grain harvests as they attract birds that are potential pests. Agroforestry principles can help to rehabilitate land to allow for higher
productivity. One way is found in “analog agroforestry” (or “succession farming”). This refers to the principle of imitating the species’ succession found in natural forests in an area, mixing annuals and perennials, in such a way that over the years, a multiple storey system can be established. Sometimes farmers are resistant to the idea of agroforestry: because of the time it takes to reap the benefits, a lack of land tenure, risks in trying something new and unknown and the new skills and knowledge required to experiment with tree growing and management.
home gardens
These small-scale systems are found close to people’s homes in (sub) humid areas, in both rural and urban zones. They tend to be managed by women. In some places, home gardens are also considered to be agroforestry systems, and are sometimes known as “forest gardens” when they have multiple storeys, consisting of crops, middle and high canopy trees. However, trees are not always part of this system. Home gardens are used to supplement food, medicines and household income. They are typified by a wide diversity of species, including local varieties, and sometimes include livestock on the same piece of land.
underutilised crops
At least 7,000 cultivated species continue to be used today around the world, mostly integrated in small-scale farming systems (including home gardens). These crops are often referred to as “neglected” or “underutilised” species. These species are a potentially important resource, for biodiversity and for household food security, since they contribute to improved nutrition and can act as buffers in times of emergency or change. They also provide many medicinal plants. However, they are often less used than other more common crops because they often require more work to prepare, due to often being smaller in size, more difficult to peel, etc. A lack of attention to these crops by research and extension institutions means that they may disappear before their potentially multiple values Go to R2.3 and discuss several
articles describing different experiences with introducing agroforestry in Brazil (analog agroforestry and cocoa), Central America (shade trees and coffee), Sri Lanka (living fences) and Ghana (introducing leguminous varieties into farms).
Go to R4.1 and watch a video about agroforestry in Guam.
Go to R2.4 to find an article from Bangladesh, where home gardens are an important source of food security.
and can open up new possibilities for small-scale integrated farming systems as well as processing and marketing opportunities.
diversity at the crop-field boundaries
Farmers can improve biodiversity by planting woody perennials along the edges of their farms, as hedgerows, for example. If managed well, these can offer different kinds of (food and market) products as well as services, such as living fences, fodder banks, shelterbelts or windbreaks. Woody perennials can help to regulate the micro-climate, cooling it through providing shade and as a barrier against wind.
Hedgerows can also encourage more biodiversity on the farm in providing habitat for insects, birds and other animals. However, they can also bring unwanted pests and weeds into the farm, if not carefully managed. Different methods to manage pests and disease are discussed in Section 2.4.
Go to R2.5 to find two articles on underutilised crops in Africa and the Pacific.
Go to R1.2 to find an exercise to research about underutilised crops in your region.
Go to 4.2 to watch a video on underutilised crops India.
1.5 sources for this learning block
• Almekinders, D.J.M., L.O. Fresco and P.C. Struik. 1995. the need to studyand manage variation in agro-ecosystems. Netherlands Journal of Agricultural Science 43: 127-142.
• Altieri, Miguel A. 1999. the ecological role of biodiversity in agroecosystems. Agriculture, Ecosystems and Environment 74: 19-31.
• Ashworth, Suzanne. 2002. seed to seed: seed saving and growing techniques for vegetable gardeners. Seed Savers Exchange, Iowa, US.
• Boddey, R. M., Runo J.R. Alves, Veronica M. Reis and Segundo Urquiaga. 2006. biological nitrogen fixation in agroecosystems and in plant roots. In: Uphoff, Norman, Andrew S. Ball, Erick Fernandes, Hans Herren, Olivier Husson, Mark Lang, Cheryl Palm, Jules Pretty, Pedro Sanchez,
Nteranya Sanginga and Janice Thies (eds). Biological approaches to sustainable soil systems. CRC Press/Taylor and Francis Group, Boca Raton, USA. pp 177-189.
• Bioversity International. 2010 why biodiversity matters; cereals. Bioversity website. Link to: www.bioversityinternational.org.
• Brookfield, Harold, Helen Parsons and Muriel Brookfield (eds). 2003. Agrodiversity: Learning from farmers across the world. The United Nations University, New York.
• FAO. 1999. Agricultural biodiversity, multifunctional character of agriculture and land conference. background paper 1. Maastricht, Netherlands.
• FAO. 2005. classification of crops. Appendix 3 in: A system of integrated agricultural censuses and surveys: World Programme for the Census of Agriculture 2010. Statistical Development Series no. 11. Food and Agriculture Organization of the United Nations, Rome, Italy. pp 142-146.
• FAO. 2010. core themes on crop production. Website of the Food and Agriculture Organization of the United Nations, Rome, Italy. Link to: www.fao. org/agriculture/crops/core-themes/en/.
• Habte, Mitiku. 2006. the roles of arbuscular mycorrhizas in plant and soil health. In: Uphoff, Norman et al. (eds). Biological approaches to sustainable soil systems. CRC Press/Taylor and Francis Group, Boca Raton, U.S.A. pp 129-147.
• Ileia editorial team. 2006. Ecological processes at work. LEISA Magazine Vol. 22 (4): 4-5.
• Kew Royal Botanic Gardens. 2000. Kew information sheet: studying plant diversity – classification. Board of Trustees, Kew Gardens, London, U.K.
• Pimbert, Michel. 2009. theme overview: women and food sovereignty. LEISA Magazine. Vol.25(3): 6-9.
• Reijntjes, Coen, Bertus Haverkort and Ann Waters-Bayer. 1992. Farming for the future: An introduction to low-external-input and sustainable agriculture. MacMillan Education Ltd. London and Oxford, U.K.
• Römheld, Volker and Neumann, Günter. 2006. The rhizosphere:
contributions of the soil-root interface to sustainable soil systems. In: Uphoff, Norman et al. (eds). Biological approaches to sustainable soil systems. CRC Press/Taylor and Francis Group, Boca Raton, U.S.A. pp 91-108.
• Thies, Janice E. and Grossman, Julie M. 2006. the soil habitat and soil ecology. In: Uphoff, Norman et al. (eds). Biological approaches to sustainable soil systems. CRC Press/Taylor and Francis Group, Boca Raton, U.S.A. pp 59-78.
