Sustainability & Environment (Agri-Food Systems) · Sustainable Agriculture & Agroecology · also Agroecology, Ecological Agriculture, Agroecosystem Analysis
Agroecology as a science, a set of practices and a social movement: ecological processes in farms, the FAO ten elements, the HLPE thirteen principles, transitions and how to assess them.
In the exams: MSc agroecology and sustainable agriculture programmes; ICAR AIEEA-PG 3.5 Organic Farming; FAO and CGIAR roles
Agroecology applies ecology to farming and food. It studies a farm as an ecosystem, in which crops, animals, soil organisms, weeds, pests and their enemies interact through flows of energy, water and nutrients, and it uses that understanding to design farms that depend less on purchased inputs and more on ecological processes. The word now carries three meanings at once: a scientific discipline, a set of farming practices, and a social movement for food sovereignty and farmer-led change. Good work in the field keeps the three apart while seeing how they connect.
The subject matters because the dominant model of the twentieth century, high-yielding varieties fed with synthetic fertiliser and protected by pesticides in simplified rotations, raised output enormously but also produced nutrient pollution, pesticide exposure, biodiversity loss, soil degradation and dependence on purchased inputs. Agroecology asks how much of the same output can be had by managing biological processes instead, where that works and where it does not, and how farmers, researchers and governments can make the change. International bodies have taken it up: FAO adopted ten elements of agroecology in 2019, and the High Level Panel of Experts on Food Security and Nutrition (HLPE) set out thirteen principles in the same year. Brazil, France and the Indian state of Andhra Pradesh, among others, have public programmes built around it.
This manual is written for MSc agroecology and sustainable agriculture courses worldwide, for the agronomy and environmental science papers of Indian postgraduate and PhD entrance tests, and for professionals in development agencies, certification bodies and agri-food companies. It assumes the basic agronomy, soil science and crop protection taught elsewhere, and concentrates on ecological processes, frameworks, transitions and evidence. Numbers are worked where examiners and practitioners use them: land equivalent ratio, energy ratios, diversity indices, nutrient balances, compost mixing, economic injury levels and assessment scores. Figures that vary by site, crop and study are given as ranges, and contested claims are labelled as contested.
Wezel and colleagues, reviewing the literature in 2009, showed that 'agroecology' is used in three ways: as a scientific discipline, as a set of agricultural practices, and as a social movement. The scientific use is the oldest. The Russian agronomist Basil Bensin used the term in the late 1920s for the application of ecology to crops, and for several decades it meant little more than crop ecology. From the 1970s and 1980s, researchers working with smallholders in Latin America, notably Miguel Altieri and Stephen Gliessman, widened it into the study of whole agroecosystems, combining ecology with the knowledge of traditional farmers. Gliessman's textbook defines agroecology as the application of ecological concepts and principles to the design and management of sustainable food systems; Francis and colleagues in 2003 proposed the even wider 'ecology of food systems', taking in processing, distribution and consumption.
As practice, agroecology refers to techniques such as intercropping, crop-livestock integration, agroforestry, cover crops, composting and biological pest control, used to strengthen ecological processes on the farm. No single practice makes a farm agroecological; what matters is how practices are combined to reduce external inputs and build internal regulation.
As a movement, agroecology is tied to peasant and indigenous organisations, notably La Vía Campesina, founded in 1993, and to the idea of food sovereignty, the right of peoples to define their own food and agriculture policies. The Declaration of the International Forum for Agroecology, held at Nyéléni in Mali in 2015, presents agroecology as a political project grounded in farmers' rights, collective knowledge and control of land, seeds and markets. This political framing is why some governments and companies prefer the narrower technical meaning, and why debates about 'co-optation' of the word are common.
Several approaches overlap with agroecology and are often confused with it. Organic agriculture is defined by certified standards that prohibit most synthetic inputs; an organic farm may be ecologically simple, and an agroecological farm may use small amounts of synthetic fertiliser, so the two are not the same. Conservation agriculture rests on three principles (minimum soil disturbance, permanent soil cover and crop diversification) and is often practised with herbicides on large farms. Sustainable intensification aims to raise yields without more land or environmental harm, and is neutral about which technologies achieve it. Regenerative agriculture is a looser label focused on soil health outcomes. Climate-smart agriculture targets productivity, adaptation and mitigation together.
Agroecology differs mainly in three ways. It puts ecological processes, especially diversity and recycling, at the centre of farm design rather than input efficiency alone; it treats farmers' knowledge as equal to scientific knowledge and favours participatory research; and, in its movement sense, it includes social questions of equity, governance and power along the food system. These differences explain why the FAO and HLPE frameworks, discussed later, include social and governance principles alongside agronomic ones.
Public programmes show the range. Brazil adopted a National Policy for Agroecology and Organic Production in 2012. France launched an agro-ecological project for its farmers in 2012 and wrote agroecology into agricultural law in 2014. In India, Andhra Pradesh began a state-wide community-managed natural farming programme in 2016, run by a not-for-profit state company with farmer self-help groups. Each defines agroecology somewhat differently, which is itself a lesson: the word is used for different mixes of science, practice and politics.
An agroecosystem is a site or unit of agricultural production understood as an ecosystem: it has living components (crops, livestock, weeds, insects, soil biota, people) and non-living ones (soil, water, climate), linked by energy flow and nutrient cycling. Compared with a natural ecosystem of the same place, an agroecosystem is usually simpler in species and structure, more open (large exports in harvested products and large imports of fertiliser, feed and fuel), younger in successional terms because cultivation keeps resetting succession, and more dependent on human control and external energy. Net primary productivity may be high, but much of it is removed, so less returns to the soil and food webs are shorter.
Agroecosystems are nested in a hierarchy: field, farm, landscape or watershed, region, and food system. Processes that matter differ by level. Nutrient recycling is often managed at field and farm level, natural pest control depends strongly on the landscape around fields, and markets and policy act at regional and global levels. Many failures of single-field research come from ignoring the level at which a process operates.
Gordon Conway proposed in the 1980s that agroecosystems be judged by four properties: productivity (output per unit of resource), stability (constancy of output in the face of normal fluctuations), sustainability (the ability to maintain productivity under stress or shock) and equitability (how evenly the products are shared among people). These properties often trade off; a highly productive system may be unstable or inequitable. The idea survives in later frameworks that add resilience, autonomy and adaptability.
Energy enters ecosystems as sunlight captured by photosynthesis and passes up food chains, with most lost as heat at each step; roughly a tenth is commonly quoted as passing from one trophic level to the next, though the true figure varies widely. Agroecosystems add 'cultural' energy: human and animal labour, and fossil energy embodied in fuel, machinery, fertiliser (nitrogen fertiliser manufacture is especially energy-intensive), pesticides and irrigation pumping.
A simple measure of energy efficiency is the energy ratio, the energy in harvested products divided by the cultural energy invested. A field that yields 45,000 MJ per hectare of grain from 9,000 MJ of inputs has a ratio of 5.0. Traditional systems that rely on human and animal labour often have high ratios but low output per hectare and per worker; heavily mechanised and fertilised systems have high output with lower ratios. Ratios depend heavily on what is counted (labour, machinery manufacture, by-products) and on the energy coefficients used, so they are compared only within one study with stated boundaries.
The ecological lesson is that agroecosystems with greater internal recycling, biological nitrogen fixation and on-farm feed need less cultural energy for the same function. This is one basis for agroecology's preference for diversified, integrated farms, though it must be weighed against labour demand and yield.
Five groups of ecological processes recur in agroecology. Primary production, the capture of light and carbon by plants, depends on leaf area, duration of cover and resource supply. Nutrient cycling moves elements between soil, plants, animals and the atmosphere; decomposition and mineralisation by soil organisms release nutrients from residues and organic matter. Population regulation keeps pests, weeds and pathogens in check through competition, predation, parasitism and disease. Succession is the directional change in communities over time, which tillage and harvest interrupt and which perennial and agroforestry systems allow to proceed further. Water regulation depends on infiltration, storage in soil and canopy cover.
Agroecological design tries to strengthen these processes by increasing diversity above and below ground, keeping the soil covered, recycling organic matter and arranging habitats in the landscape. Two concepts organise the reasoning. Functional diversity is the variety of functions performed by species in the system (fixing nitrogen, deep rooting, attracting natural enemies) rather than the number of species alone. Ecosystem services are the benefits people obtain from ecosystems; agroecosystems both receive services, such as pollination and natural pest control, and supply them, such as food, water regulation and carbon storage, while also generating disservices such as pest damage and nutrient loss.
Diversity on farms takes several forms: genetic diversity within a crop (varieties and landraces), species diversity (several crops and animals), structural diversity (layers of vegetation, as in agroforestry), temporal diversity (rotations and relay crops) and landscape diversity (hedgerows, field margins, woodland and wetland patches). Below ground, diversity of soil organisms underpins decomposition and nutrient cycling.
Diversity helps through several mechanisms. Complementarity arises when species use resources differently, for example deep- and shallow-rooted crops, or a legume fixing nitrogen while a cereal takes up soil nitrogen. Facilitation arises when one species improves conditions for another, as when a legume's fixed nitrogen later benefits a cereal, or a taller crop shades a shade-tolerant one. Insurance arises because varied species respond differently to weather and pests, so total output fluctuates less. Diversity also supports natural pest regulation, discussed in Chapter 5.
A well-documented example of within-crop diversity comes from Yunnan in China, where Zhu and colleagues reported in Nature in 2000 that planting a susceptible glutinous rice variety in mixtures with resistant hybrid rice greatly reduced rice blast and raised yields compared with monocultures, without fungicide. The example shows that diversity can be designed for a function, not added at random.
Intercropping grows two or more crops together on the same field for at least part of their life. Forms include mixed intercropping (no distinct rows), row intercropping, strip intercropping (strips wide enough to manage separately) and relay intercropping (a second crop sown into the first before its harvest). Classic examples are cereal-legume combinations: maize with beans, sorghum with pigeonpea, millet with cowpea.
The land equivalent ratio (LER) measures whether an intercrop uses land more efficiently than sole crops. LER is the sum, over the crops, of the intercrop yield divided by the sole-crop yield of the same crop: LER = (Ya intercrop / Ya sole) + (Yb intercrop / Yb sole). An LER above 1 means that more land would be needed to produce the same amounts as sole crops. If maize yields 3.2 t/ha in the intercrop and 4.0 t/ha alone, and beans yield 1.2 t/ha in the intercrop and 1.6 t/ha alone, LER = 0.80 + 0.75 = 1.55: sole crops would need 55 percent more land. LER compares land use only; it ignores the relative value of the crops, labour and the fact that the intercrop may be sown at different densities, so it is read alongside economic measures.
Vandermeer's competitive production principle explains when intercrops overyield: when the species interfere with each other less than each interferes with itself, combined yield per unit area exceeds that of the sole crops. Facilitation adds to this. Where competition between the crops is stronger than within them, LER falls below 1.
Synergy means that combining components gives more than the sum of their separate effects. Crop-livestock integration is the commonest example: crop residues feed animals, manure returns nutrients to fields, animals use land unsuited to crops and draught animals supply power. Rice-fish and rice-duck systems in Asia combine grain with animal protein while the animals eat weeds and insects and add nutrients; in the push-pull system developed in East Africa by the International Centre of Insect Physiology and Ecology (icipe), maize is intercropped with the legume Desmodium, which repels stemborer moths and suppresses the parasitic weed Striga, while a border of Napier or Brachiaria grass attracts the moths away from the maize, and both companion plants provide fodder.
Agroforestry systems, trees combined with crops or animals, add vertical structure, perennial roots, shade, fodder, fuel and fruit; the agroforestry subject of this track treats them in detail. Home gardens in the humid tropics, such as those of Kerala and Java, combine many layers and species on small plots and are often cited as models of high diversity with continuous harvest.
Diversity has costs: more knowledge, more labour, more difficult mechanisation and sometimes lower yield of the main crop. Agroecology does not claim that more diversity is always better, but that functional diversity chosen for a purpose usually makes farms less dependent on external inputs and less vulnerable to shocks.
Every farm has nutrient inputs (fertiliser, manure and feed brought in, biological nitrogen fixation, atmospheric deposition, irrigation water), internal flows (crop residues, manure, compost, litter) and outputs (crop and animal products sold, and losses by leaching, runoff, erosion and gaseous emission). Agroecology aims to close cycles: to increase internal recycling, reduce losses and replace part of the purchased inputs with biological sources.
A nutrient balance compares inputs with outputs. A farm-gate balance counts what crosses the farm boundary; a soil-surface balance counts what enters and leaves the soil. A positive balance (surplus) means nutrients accumulate or are lost to the environment; a negative balance (deficit) means the soil is being mined. For example, a hectare receiving 60 kg N in fertiliser, an estimated 40 kg N from legume fixation, 30 kg N in manure and 10 kg N from deposition, and exporting 4 t of grain at 1.8 percent N (72 kg N), has a surplus of 140 minus 72 = 68 kg N per hectare. Surpluses in intensive regions and deficits in many smallholder systems of sub-Saharan Africa are both sustainability problems; agroecology therefore does not simply mean fewer inputs everywhere.
Nitrogen use efficiency, the share of nitrogen inputs recovered in products, summarises the same information; global estimates for cropland are commonly put at well under one half, with wide variation by country and system.
Legumes in symbiosis with rhizobia fix atmospheric nitrogen in root nodules. The amount fixed varies very widely with species, soil nitrogen, phosphorus supply, moisture and management, from almost nothing to a few hundred kilograms per hectare per season, and much of it leaves in harvested grain; grain legumes therefore leave less residual nitrogen than green manures or forage legumes whose whole biomass is returned. Free-living and associative bacteria fix smaller amounts. Azolla, a water fern with a nitrogen-fixing cyanobacterium, has long been used in Asian rice fields.
Arbuscular mycorrhizal fungi colonise the roots of most crops and extend the effective root system, improving uptake of phosphorus and other immobile nutrients and helping soil aggregation; tillage, fallow and heavy phosphorus fertiliser reduce them, and brassicas and beet do not host them. Earthworms, microarthropods and microbes break down residues, form aggregates and build organic matter. Soil organic matter is the central store of nutrients and water in low-input systems, and its management (residue return, manure, cover crops, reduced tillage) links nutrient cycling to soil health.
Composting is the controlled aerobic decomposition of organic materials into a stable product. Microbes need a balanced diet: an initial carbon-to-nitrogen ratio of about 25 to 30 to 1 is commonly recommended, with moisture around 50 to 60 percent and regular aeration. Materials rich in carbon (straw, dry leaves, sawdust) are mixed with materials rich in nitrogen (manure, green leaves, food waste). Too much nitrogen leads to ammonia loss and odour; too much carbon slows decomposition.
Mixing is calculated from carbon and nitrogen contents, not from the C:N ratios alone. Straw with 40 percent carbon and 0.5 percent nitrogen (C:N 80) mixed with manure with 30 percent carbon and 2 percent nitrogen (C:N 15) reaches a C:N of 30 when (0.40x + 0.30) / (0.005x + 0.02) = 30, where x is kilograms of straw per kilogram of manure; solving gives x = 1.2. Thermophilic composting, which reaches about 55 degrees C or more for several days, kills many weed seeds and pathogens. Vermicomposting uses earthworms at lower temperatures.
Manure is a resource and a pollutant. Nitrogen is lost as ammonia from uncovered heaps and surface-spread manure, as nitrate by leaching and as nitrous oxide; covering stores, incorporating manure quickly and applying it when crops can use it reduce losses. In mixed farms the manure cycle is the main tool for moving nutrients from grazing land to crop land, which is why the loss of livestock from many farms broke traditional nutrient cycles.
Pests, weeds and diseases are regulated in nature by competition, predation, parasitism, disease and plant defence. Simplified agroecosystems weaken these controls: large areas of one crop provide concentrated food for specialist herbivores, and broad-spectrum pesticides kill natural enemies as well as pests, sometimes causing pest resurgence and secondary pest outbreaks.
Two classic hypotheses explain why diverse plantings often have fewer specialist pests. The resource concentration hypothesis, proposed by Root in 1973, holds that specialist herbivores find, stay on and multiply on host plants more readily when hosts grow in dense, pure stands. The enemies hypothesis holds that diverse habitats support more predators and parasitoids by providing alternative prey, nectar, pollen and shelter. Reviews find that diversification on average reduces herbivores and increases natural enemies, but effects vary and some mixtures favour pests.
Biological control comes in three forms. Classical biological control introduces natural enemies from a pest's region of origin against an invasive pest. Augmentative control releases natural enemies, either in large numbers for immediate effect (inundative) or in small numbers to establish (inoculative). Conservation biological control, the form most central to agroecology, manages habitats and practices so that existing natural enemies thrive.
Habitat management provides natural enemies with food, shelter and overwintering sites. Flowering strips and field margins supply nectar and pollen to parasitoid wasps and hoverflies; beetle banks, grassy ridges across fields, shelter ground beetles and spiders; hedgerows and woodland patches act as refuges. Effects depend on the landscape: in already complex landscapes, extra local habitat may add little, while in very simple landscapes local measures may not be enough because enemy populations are too small. Reducing pesticide use, choosing selective products and timing sprays to spare enemies are part of the same strategy.
Behavioural manipulation uses plant chemistry. In push-pull, a repellent intercrop pushes pests away from the main crop while an attractive trap plant around the field pulls them out; the East African maize system with Desmodium and Napier or Brachiaria grass is the best known. Trap crops alone, such as a more attractive variety around the edge of a field, concentrate pests where they can be controlled. Allelopathy, chemical suppression of one plant by another, and competitive cover crops help manage weeds; crop rotation breaks the life cycles of soil-borne diseases and host-specific weeds.
Integrated pest management (IPM) combines prevention, monitoring and intervention only when needed. Its central decision tool is the economic injury level (EIL), the lowest pest density that causes damage worth as much as the cost of control. In Pedigo's formulation, EIL = C / (V x I x D x K), where C is the cost of control per hectare, V the value of the produce per unit, I the injury per pest, D the yield loss per unit of injury, and K the proportion of injury the control prevents. If C is 1,500 currency units per hectare, V is 25 per kilogram, each insect per hectare causes 0.5 kg of loss (I x D) and control prevents 80 percent of injury, EIL = 1,500 / (25 x 0.5 x 0.8) = 150 insects per hectare. The economic threshold (action threshold) is set below the EIL so that control can act before the EIL is reached.
Agroecology treats IPM as a step on the way, not the end point: the aim is to redesign the system so that pest problems rarely reach thresholds, through diversity, healthy soils, resistant varieties and natural enemies, with targeted intervention as a last resort. Farmer Field Schools, which began in Indonesian rice IPM programmes in 1989, show how this knowledge can be learned through field observation of pests and natural enemies.
FAO held an International Symposium on Agroecology for Food Security and Nutrition in Rome in 2014, followed by regional meetings and a second international symposium in 2018. From these discussions FAO drew up the ten elements of agroecology, which the FAO Council endorsed in December 2019 as a guide for countries planning transitions. The ten elements are: diversity; co-creation and sharing of knowledge; synergies; efficiency; recycling; resilience; human and social values; culture and food traditions; responsible governance; and circular and solidarity economy.
FAO groups them. Diversity, co-creation and sharing of knowledge, synergies, efficiency, recycling and resilience describe common characteristics of agroecological systems, their foundational practices and innovation approaches. Human and social values, and culture and food traditions, are context features. Responsible governance and circular and solidarity economy describe the enabling environment. The elements are interlinked and are not meant to be scored one by one in isolation; they serve as an analytical framework and as the basis of FAO's assessment tool, TAPE (Chapter 11).
Diversity is described as key to agroecological transitions, covering species, genetic resources and the landscape, and supporting nutrition and resilience. Co-creation and sharing of knowledge emphasises that innovations respond best to local challenges when farmers and researchers create them together, through participatory processes. Synergies are the interactions that enhance ecosystem functions, such as crop-livestock integration. Efficiency means producing more with fewer external resources, by using natural processes. Recycling means more reuse of nutrients, biomass and water within farms and landscapes, lowering cost and environmental harm. Resilience is the capacity of people, communities and ecosystems to recover from disturbances such as extreme weather, drought, pests or price shocks.
Human and social values (dignity, equity, inclusion and justice) are presented as essential to sustainable livelihoods, with particular attention to women and youth. Culture and food traditions recognise that healthy, diversified and culturally appropriate diets are part of the food system. Responsible governance calls for transparent, accountable and inclusive mechanisms at local to global scales, including secure access to land and natural resources. Circular and solidarity economy refers to markets that reconnect producers and consumers, such as local markets, community-supported agriculture and public procurement, and to keeping value in local economies.
The framework is broad by design. Critics note that it is hard to measure and that elements like efficiency are claimed by conventional intensification too; supporters reply that the elements are meant to be read together, so that efficiency without diversity, recycling and equity is not agroecology in FAO's sense.
The High Level Panel of Experts on Food Security and Nutrition (HLPE) advises the Committee on World Food Security (CFS). Its fourteenth report, published in 2019, compared agroecological and other innovative approaches to sustainable agriculture and food systems. It set out thirteen agroecological principles, consolidated from earlier lists, and grouped them under three operational principles: improve resource efficiency, strengthen resilience, and secure social equity and responsibility. It also linked each principle to the scale at which it mainly applies: field, farm or agroecosystem, and food system. The CFS later negotiated policy recommendations on agroecological and other innovative approaches, adopted in 2021.
The HLPE report also distinguished between approaches that improve the efficiency of current systems (such as sustainable intensification) and those that seek transformation (such as agroecology), and stressed that the choice depends on context and values. It identified knowledge, power and governance as recurring barriers to transition, and called for research systems that value farmers' knowledge and measure performance across environmental, social and economic outcomes rather than yield alone. For students, the report is useful as a map of the approaches that compete for the label 'sustainable': it describes sustainable intensification, climate-smart agriculture, nutrition-sensitive agriculture, organic farming, agroforestry, permaculture and food sovereignty, and shows where each sits between efficiency and transformation.
Under improving resource efficiency are two principles: 1, recycling, preferentially using local renewable resources and closing resource cycles of nutrients and biomass; and 2, input reduction, reducing or eliminating dependency on purchased inputs. Under strengthening resilience are five: 3, soil health, securing and enhancing soil health and functioning for plant growth, particularly by managing organic matter and enhancing soil biological activity; 4, animal health, ensuring animal health and welfare; 5, biodiversity, maintaining and enhancing diversity of species, functional diversity and genetic resources over time and space; 6, synergy, enhancing positive ecological interaction, synergy, integration and complementarity among the elements of agroecosystems; and 7, economic diversification, diversifying on-farm incomes so that small-scale farmers have greater financial independence.
Under securing social equity and responsibility are six: 8, co-creation of knowledge, enhancing co-creation and horizontal sharing of knowledge, including local and scientific innovation; 9, social values and diets, building food systems based on the culture, identity, tradition and social and gender equity of local communities that provide healthy, diversified, seasonally and culturally appropriate diets; 10, fairness, supporting dignified and robust livelihoods for all actors in food systems, especially small-scale producers, based on fair trade, fair employment and fair treatment of intellectual property rights; 11, connectivity, ensuring proximity and confidence between producers and consumers through fair and short distribution networks; 12, land and natural resource governance, strengthening institutional arrangements and recognising and supporting family farmers, smallholders and peasant producers as sustainable managers of natural and genetic resources; and 13, participation, encouraging social organisation and greater participation in decision-making by food producers and consumers.
The thirteen principles and the ten FAO elements cover much the same ground; the principles are more specific (for example, they separate soil health and animal health) and easier to turn into indicators. Examiners often ask students to map one onto the other.
A transition is the process by which a farm or food system moves from a conventional, input-intensive configuration towards an agroecological one. Hill and MacRae in Canada described three stages in the 1990s: efficiency (using inputs more precisely), substitution (replacing harmful inputs and practices with more benign ones) and redesign (reorganising the system so that ecological processes do the work). Gliessman built on this with a framework of levels, now usually given as five.
Level 1 is increasing the efficiency of conventional practices to reduce the use and consumption of costly, scarce or environmentally damaging inputs: for example, precise fertiliser timing or threshold-based spraying. Level 2 is substituting alternative practices and inputs for conventional ones: replacing a synthetic insecticide with a biopesticide, or synthetic fertiliser with compost, while keeping the same system structure. Level 3 is redesigning the agroecosystem so that it functions on the basis of a new set of ecological processes: diversified rotations, intercrops, crop-livestock integration and habitat for natural enemies make many problems disappear rather than needing substitutes. Levels 1 and 2 are incremental; level 3 is transformational at farm level.
Level 4 is re-establishing a more direct connection between those who grow food and those who consume it: community-supported agriculture, farmers' markets, box schemes, cooperatives and public procurement, which give farmers fairer prices and consumers knowledge of how food is produced. Level 5, added by Gliessman later, is building a new global food system, based on equity, participation, democracy and justice, that restores and protects the earth's life-support systems. Levels 4 and 5 take agroecology beyond agronomy into economics and politics.
Transitions take time. Soil biology, organic matter, natural enemy populations and farmer knowledge build up over several seasons, and yields of some crops may dip during the first years after inputs are reduced, before redesign takes effect. Farmers therefore often move field by field, and need advice, credit, markets and sometimes compensation during the transition. Research on 'lock-in' explains why many farms remain at levels 1 and 2: machinery, contracts, subsidies, knowledge systems and market standards are built around simplified systems.
Transition frameworks are also used to classify practices and policies. A national programme that only subsidises biofertilisers is supporting level 2; one that funds farmer-to-farmer learning, diversified rotations and local markets is working at levels 3 and 4.
Traditional and indigenous farming systems, developed over centuries by trial and selection, often show features that agroecology seeks: high diversity, efficient use of local resources, recycling, and adaptation to difficult environments with few external inputs. Studying them is not nostalgia; they are tested designs that can be analysed, adapted and combined with modern knowledge. They also have limits: low labour productivity, vulnerability when population density or markets change, and sometimes inequitable social arrangements.
Examples recur in the literature. The Mesoamerican milpa intercrops maize, beans and squash, often with other species, combining nitrogen fixation, ground cover and complementary diets. Chinampas, raised beds built in shallow lakes in the Valley of Mexico, recycled lake sediment and aquatic plants as fertiliser. Waru waru raised fields around Lake Titicaca alternate raised beds with water-filled canals that moderate night frost. Zaï pits in the Sahel of Burkina Faso and Niger concentrate water and manure in small planting holes on crusted soils. Rice-fish co-culture in southern China and terrace systems in the Philippine Cordillera manage water, nutrients and pests together. Tropical home gardens and shifting cultivation with long fallows, such as jhum in north-east India, are further examples; shifting cultivation becomes unsustainable when fallows are shortened.
Indigenous and local knowledge includes classifications of soils, plants and pests, indicators of weather and soil fertility, seed selection and exchange networks, and rules for sharing water, grazing and forests. It is held collectively and transmitted orally and through practice. Agroecology treats it as a source of hypotheses and solutions, while recognising that it is not uniform or always correct and that it must be engaged with on fair terms; the rights of communities over traditional knowledge and genetic resources are protected in instruments such as the Convention on Biological Diversity's Nagoya Protocol and the International Treaty on Plant Genetic Resources for Food and Agriculture.
FAO's Globally Important Agricultural Heritage Systems (GIAHS) programme, launched in 2002, recognises traditional systems of outstanding value for biodiversity, livelihoods and culture. The rice-fish culture of Qingtian in China was among the first sites designated. Indian sites include the saffron heritage of Kashmir, the traditional agriculture of Koraput in Odisha and the below-sea-level farming system of Kuttanad in Kerala. Designation brings attention and sometimes support, but conservation depends on whether the systems remain economically viable for the families who maintain them.
Three cautions apply. First, a practice that works in one place depends on its ecological and social context; zaï pits need manure and labour, and rice-fish culture needs reliable water and secure tenure. Second, traditional systems were often maintained by institutions (communal labour, customary land rules, religious calendars) that may have weakened. Third, traditional varieties and practices may give low yields under modern population pressure. The useful approach is hybrid: keep the principles (diversity, recycling, cover, water harvesting) and test improved versions with farmers, as with improved zaï pits combined with microdosing of fertiliser, or milpa systems intercropped with fruit trees. Researchers who work this way document the logic of a traditional practice first, through interviews and measurements, then propose small changes that farmers test and judge. They also record who holds the knowledge, often women for seeds and home gardens, so that the people who maintain a system share in any benefit from its study or promotion.
Agroecological practices are knowledge-intensive and site-specific: the best intercrop, cover crop or habitat strip depends on local soils, climate, pests and markets. Centralised research and one-way extension, which worked for standard packages of seed and fertiliser, transfer such knowledge poorly. Agroecology therefore favours research and learning in which farmers take part in setting questions, running trials and judging results.
Participation has degrees, from consultation (researchers ask farmers' opinions) through collaboration (farmers manage trials designed with researchers) to collegiate or farmer-led research (farmers set the agenda and researchers support). Participatory action research combines research with action for change. Participatory plant breeding involves farmers in selecting varieties and parents from early generations, often in marginal environments where formal breeding has done less well. Methods such as transect walks, seasonal calendars, resource-flow maps and ranking exercises, many drawn from participatory rural appraisal, help outsiders understand farm systems. Participation is not automatically fair: more powerful or better-off farmers may dominate groups, and women's time constraints may keep them out of meetings, so facilitators must design for inclusion.
Farmer Field Schools (FFS) were developed in FAO-supported rice IPM programmes in Indonesia from 1989. A group of farmers meets weekly through a season in a field, observing and analysing the crop ecosystem, especially pests and natural enemies, and comparing practices in a learning plot. The approach spread to many crops and countries. Evaluations generally find gains in knowledge and reduced pesticide use among participants, with debate about how far these spread to non-participants and how cost-effective the schools are at scale.
The campesino a campesino (farmer-to-farmer) movement began among Kaqchikel Maya farmers in Guatemala in the 1970s and spread to Mexico, Nicaragua and Cuba, where the National Association of Small Farmers (ANAP) adopted it from 1997. Farmers who have tried a practice successfully become promoters who teach others through demonstration on their own farms. The method spreads practices horizontally, uses farmers' language and credibility, and builds social organisation. Cuba's experience after the loss of Soviet inputs in the early 1990s is widely cited, though the drivers of its transition included economic necessity and state policy as well as the method.
Large public programmes in India have used similar ideas. Andhra Pradesh's community-managed natural farming programme relies on experienced farmers as community resource persons and on women's self-help groups to spread practices village by village; independent evaluations of its yields, costs and incomes are still accumulating and should be read with attention to method.
Yield per hectare is the usual measure of agricultural performance, but it captures only one output of one crop. Agroecological systems produce several products, use fewer purchased inputs, provide environmental services and aim at social goals, so they are assessed on several dimensions at once: environmental, economic, social and sometimes governance. The challenge is to choose a manageable set of indicators, measure them comparably and interpret them with the people concerned.
Several frameworks exist. MESMIS, developed in Mexico in the late 1990s, assesses sustainability through attributes such as productivity, stability, resilience, adaptability, equity and self-reliance, translated into locally chosen indicators and compared between a reference and an alternative system. FAO's SAFA guidelines (Sustainability Assessment of Food and Agriculture systems) define themes across good governance, environmental integrity, economic resilience and social well-being. Farm-level tools used in Europe include RISE and IDEA. FAO's SHARP tool focuses on climate resilience of pastoralists and farmers.
FAO's Tool for Agroecology Performance Evaluation (TAPE), released in 2019 and refined in 2020, is designed to be used across countries with modest cost. It has several steps. Step 0 describes the context of the farm and territory. Step 1, the Characterisation of Agroecological Transition (CAET), scores the farm on indices grouped under the ten FAO elements; each index is scored from 0 to 4 on descriptive scales, the scores of each element are averaged and expressed as a percentage, and the overall CAET is the mean across elements. Step 2 measures core performance criteria, ten in the standard version: secure land tenure, productivity, income, added value, exposure to pesticides, dietary diversity, women's empowerment, youth employment opportunities, agricultural biodiversity and soil health. Step 3 is a participatory interpretation of results with farmers and stakeholders.
A worked example shows the arithmetic of one element. If the diversity element has four indices scored 3, 2, 4 and 3, their mean is 3.0 out of a maximum of 4, which is 75 percent for that element. If the ten element scores range from 40 to 75 percent and average 58 percent, the farm's overall CAET is 58 percent. CAET results are used to classify farms along the transition and to relate the degree of agroecology to the performance criteria measured in Step 2.
Assessment results depend on sampling, the honesty of self-reported data and the scales used. Single-visit surveys capture one season; comparison with conventional neighbours needs matched samples; and correlation between CAET scores and performance does not prove that agroecology caused the difference. Good practice reports sample design, uncertainty and context with the scores.
The most contested question is whether agroecological and organic systems can feed the world. Meta-analyses comparing organic and conventional yields provide the main evidence, because many agroecological practices are tested within organic systems. Seufert, Ramankutty and Foley (2012) estimated that organic yields were on average about 25 percent lower than conventional, with the gap varying from small for some legumes and perennials under good management to large for cereals. Ponisio and colleagues (2015), with a larger dataset, estimated a gap of about 19 percent, which narrowed to around 8 to 9 percent when organic systems used multicropping or crop rotations. These figures are averages over very different studies, mostly from high-income countries, and do not settle the question for smallholder systems where conventional inputs are often used poorly.
Several points cut both ways. Yield per hectare of the main crop understates the total output of diversified systems, which LER and whole-farm measures capture better. Lower yields may mean more land is needed, which is the heart of the 'land sparing versus land sharing' debate: sparing argues for high-yield farming on less land with more set aside for nature, sharing for wildlife-friendly farming across larger areas. Evidence suggests the answer depends on the species and landscape, and that the two can be combined.
Scaling out means spreading agroecology to more farmers; scaling up means changing institutions, policies and markets so that it becomes easier. Studies of successful cases point to recurring drivers: a sense of crisis that makes change necessary, social organisation of farmers, constructive teaching methods such as farmer-to-farmer learning, effective practices that show results, mobilising discourse, external allies, favourable markets and favourable policy. Lacking these, promising pilots stay pilots.
Policy can help or hinder. Supportive measures include public research and extension for agroecology, payment for environmental services, public procurement from family farms (as in Brazil's school-meal and food purchase programmes), secure land tenure and support for local markets. Policies that subsidise synthetic inputs or reward single-commodity yields push the other way. The European Union's Farm to Fork strategy set a target of 25 percent of agricultural land under organic farming by 2030.
Abrupt, top-down change can fail badly. In 2021 Sri Lanka banned imports of synthetic fertilisers and pesticides almost overnight to move to organic farming; rice and tea output fell sharply, and the policy was reversed within months. Most agroecologists cite the episode as a lesson that transitions need time, knowledge, alternative nutrient sources and farmer participation, not as evidence for or against agroecology itself.
Critics argue that agroecology is knowledge- and labour-intensive, that its practices are hard to mechanise on large farms, that biological nitrogen supply limits yields, that its political framing deters engagement with private research and modern biotechnology, and that the evidence base relies too much on case studies. Supporters respond that labour may be an opportunity where rural employment is needed, that redesign reduces costs and risk even when yields are similar, that long-term experiments show soil and resilience benefits, and that the comparison should include environmental and health costs not counted in market prices. Rigorous evaluation, with matched comparisons, long time series and full accounting of outputs and costs, is the way to move this debate forward. Students should be able to state each side's best argument and the evidence that would change their view, rather than repeat slogans from either camp. A useful exercise is to take one claim, for example that agroecology raises net income, and ask: compared with what, measured how, over how many seasons, on which farms, and with whose labour counted.
Learn the core frameworks well enough to compare them: the three meanings of agroecology, Conway's properties, the FAO ten elements and their three groups, the HLPE thirteen principles and their three operational groups, and Gliessman's five levels. Practise the calculations by hand: land equivalent ratio, energy ratio, Shannon and Simpson diversity, farm nutrient balances, compost mixing from carbon and nitrogen contents, economic injury levels and CAET percentages. On field visits, draw the nutrient flows of one farm, list its sources of diversity and their functions, and place its practices on the transition levels. Read at least one meta-analysis of organic and conventional yields and note what it does and does not show.
In an NGO, extension service, certification body or agri-food company, you design and support transitions. Typical tasks: diagnose a farm's nutrient balance and suggest legumes, compost or manure changes; set up habitat strips or push-pull trials with farmer groups; run a Farmer Field School; apply TAPE or a similar tool to a sample of farms and present results back to the community; and advise on markets that reward diversified production. The key judgement is matching practices to the local context and to the farmer's labour, land and cash constraints, and being honest about early yield dips and the time redesign takes.
At programme or policy level, you decide where public money goes: research and extension for agroecology, payment for ecosystem services, public procurement from family farms, and reform of input subsidies. You evaluate programmes such as state-wide natural farming or national agroecology plans with proper comparison groups and multidimensional indicators, and you negotiate with ministries, donors and companies about definitions and claims. Experience shows that successful scaling combines farmer organisation, farmer-to-farmer methods, effective practices, markets and supportive policy; you build those conditions rather than promoting a single practice. You also guard against both greenwashing, where the word is attached to minor input substitution, and overclaiming, where pilot results are presented as proven at scale.
Research questions remain open and important: the mechanisms and limits of overyielding in intercrops and mixtures, landscape effects on natural pest control, nitrogen supply from biological sources at scale, long-term yields and resilience of redesigned systems under climate change, robust and comparable performance metrics, and the social and political conditions for scaling. Good research combines long-term field experiments, on-farm networks and participatory methods with rigorous statistics and causal inference, and states plainly where evidence is thin or comes mainly from case studies. Senior researchers also train the next generation in participatory methods, sit on bodies such as the HLPE or national committees that define agroecology in policy, and help build the long-term datasets the field still lacks.
This manual gives frameworks and processes, not crop-by-crop recommendations; intercrop combinations, legume nitrogen contributions, compost recipes and pest thresholds must be set locally. Figures such as nitrogen fixed by legumes, energy ratios, trophic transfer efficiency and yield gaps are given as ranges or as study-specific averages because they vary widely. Independent evaluations of large programmes such as Andhra Pradesh natural farming are still accumulating, so no yield or income effect is stated. National agroecology policies are named, not described in detail, and policies after 2025 are not covered. Organic certification, conservation agriculture, agroforestry, nutrient stewardship and pesticide impacts each have their own subject in this track and are treated here only where they illustrate agroecological principles. The landscape ecology of pest control, soil food webs and the economics of transitions are introduced but not developed quantitatively.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
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