Agroecological Intensification of Smallholder Farming
Abstract and Keywords
The smallholder farmers who cultivate many of the planet’s diverse production systems are faced with numerous challenges, including poverty, shrinking farm sizes, degrading natural resources, and climate variability and change. Efforts to improve the performance of smallholder farming systems focus on improving access to input and output markets, improving farm resource use efficiency, and improving resources invested in smallholder farming. In order to support market-oriented production and self-provisioning, there is a need for greater focus on agroecological intensification (AEI) of smallholder production systems. This chapter provides an overview of some of the research frontiers supporting AEI. Market-oriented and agroecological approaches may or may not conflict, and more effort should be made to ensure that they are mutually reinforcing. To be reliable, value chains must be founded on sound production ecology. Agroecological options may be limited if farmers cannot participate in markets that support investment in the intensification and diversification of these systems. Because options must be adapted to farmers’ heterogeneous and dynamic contexts, successful AEI will require that specifics be optimized locally. Researchers must therefore understand and communicate relevant agroecological principles, and farmers and intermediaries must develop their capacity to adapt the principles to local needs and realities.
The food price crisis of 2007 focused the attention of scientists, policy bodies, activists, and corporations on the precarious state of global food production systems. Major journals have dedicated special issues to food security. Science magazine dedicated a special issue to the subject of food security on February 12, 2010, and Nature’s special issue of July 28, 2010 asked “Can Science Feed the World?” The Economist recently featured cover stories on food security several times, and in 2011 Foreign Policy had a first-ever “food issue” titled “Inside the Geopolitics of a Hungry Planet.” The problems that threaten the productivity and stability of agriculture are hardly new, however; climate challenges, energy prices, and degrading agrobiological resources have long afflicted smallholder farmers.
Agricultural systems are required not only to produce food, but also to provide livelihoods for millions of resource-limited smallholder farmers. In most countries, the majority of people participate in agriculture (World Bank 2007). Most of the poorest billion people (70 percent) rely on agriculture for their livelihoods. Agriculture, as the major use of managed land globally, also has to contribute to the maintenance of ecosystems and the provision of ecosystem services. Agricultural systems are failing on a grand scale, however, and ecosystem services are in critical decline (Millenium Ecosystems Assessment 2005). In addition, nearly a billion people are currently undernourished, and the global population is expected to increase from seven to nine billion by 2050 (Bongaarts 2009).
While there is a general consensus that there is a need to increase food production and improve rural livelihoods without further undermining the earth’s productive (p. 106) capacity, there is diversity of opinion on how this may be best achieved. Much of the increased productivity attained in Africa over recent decades has relied upon increasing the land area utilized, but there are few remaining opportunities to expand agricultural areas without conflict and excessive environmental damage (Young 1999; Balmford et al. 2012). Thus it is generally agreed that some sort of intensification is essential (Pretty et al. 2011). Increased production per unit area has historically been driven by technology change, much of it dependent on cheap fossil fuel inputs. The concept of intensification is often assumed to refer to the increased use of purchased inputs, such as improved seed, fertilizer, and irrigation to produce higher crop yields. It is, however, possible to intensify production based on an increased use of ecological knowledge and practices, or on a combination of ecological practices and purchased inputs. The outputs can be measured in terms of higher yields, but metrics can also include ecosystems services, nutrition, and livelihoods. Contemporary development discourse reflects these alternatives. In this chapter we examine what this means for smallholder farmers in developing countries, and for the systems that support them.
Alternative Trajectories and Strategies for Achieving Them
From the most simplistic point of view, three types of trajectories can be described for agricultural systems: those in which performance is being degraded (those following degenerative pathways), those in which performance is stable, and those in which performance is sustainably improving (those on regenerative pathways). How “performance” is defined is critical; that issue will be addressed below. The natural endowments, history, pressures, and constraints differ across systems, so in reality an infinite number of trajectories could be described. Research and development efforts aim to identify practical opportunities to nudge trajectories in a way that improves the performance of these systems.
Unfortunately, many of the world’s farming systems are on degenerative trajectories, in which the basic agro-resources of soil, water, and genetic resources are being eroded. The Millennium Ecosystem Assessment determined that 40 percent of farmland is being critically degraded (Millenium Ecosystem Assessment 2005). Even many of the best-endowed African agroecosystems are under sufficient population pressure that their productivity has been compromised or is likely to be negatively affected in the near future (MacIntyre et al. 2009). Degradation of agricultural resources can be the consequence of intensification: irrigation can lead to groundwater depletion and to salinization; reduction in fallows can lead to reduced soil fertility; the overuse of chemical inputs can lead to pollution and to pest outbreaks; and tillage can lead to soil erosion. Degradation can also result from neglect. When inputs are not provided and fallows are shortened or eliminated, for example, soil fertility can be exhausted. When agriculture (p. 107) is extended to rainforests, hillsides, and other fragile environments, soil is typically eroded.
How can systems that are currently following degenerative trajectories be shifted to stable or regenerative ones? Reflecting on the need for transformative change to put the planet on the path to sustainability, Leach et al. (2012) point out the need for new technologies, new policies, and new modes of innovation. They define three dimensions requiring consideration: direction (where are we going?), diversity (how can we acknowledge and address the multiplicity of contexts and issues with correspondingly diverse approaches and forms of innovation?) and distribution (who are the winners and losers of any given approach?). Considering the direction to be taken implies being clear about the goals and principles to be applied. The goal of improving agricultural productivity alone would lead to a different direction than the goal of equitably improving food security. If the goal of protecting species diversity were also considered, that would again call for a different direction to be taken.
A focus on the goal of improving agricultural productivity could lead to a focus on the industrialization of large-scale agriculture. While this could succeed in producing greater surpluses that could benefit urban populations through lower prices, it could also lead to the marginalization and elimination of smallholders and the expansion of urban slums, as well as increasing the pressure on many ecosystem services. Half of the world’s food insecure people are rural smallholder farmers (Cohen 2008); the goal of increasing their productivity might lead to a focus on improving input and output markets. While this would benefit those within reach of population centers, market-based approaches might increase ecological and market risks, and they would not inevitably improve food security. In sub-Saharan Africa, more than 30 percent of the rural population has poor access to markets (World Bank 2007). For this reason and others, substantial proportions of smallholder farmers consume the majority of what they produce. In 2004, for example, 80 percent of Nigerian farmers were classified as subsistence-oriented farmers (Davis et al. 2007, as cited in World Bank 2007). Helping these farmers to integrate into markets is a laudable goal, but market-based approaches are more likely to squeeze out resource-poor smallholders than to include them (Hartman 2012).
A focus on food security would have to acknowledge that increasing productivity is necessary but not sufficient to improve the food security of resource-poor people. The widely accepted definition of food security (USAID 1992) includes dimensions of availability, access, and utilization; some definitions also include aspects of risk and sustainability (FAO 2006). The access dimension implies financial as well as logistical access to food, and thus brings in elements of equity among and within households. The utilization dimension brings in nutritional considerations, as do qualitative aspects of the availability dimension. Thus, improving food security of the rural poor must entail improving market access for smallholders and increasing their employment options, but it must also improve the livelihoods of those engaged in subsistence or semi-subsistence farming.
The goals and principles of agricultural development strategies can and must go beyond concerns for food production and food security. Agriculture’s multifunctionality (p. 108) is increasingly appreciated in wealthy countries, and accordingly a greater diversity of products and services are being demanded of agriculture (Van Acker 2008; Renting et al. 2009). Similarly, it is recognized that smallholder farming must also serve many needs for producers as well as the larger landscapes and populations (Amekawa et al. 2010). Agricultural policies will influence equity, dietary diversity, and environmental services such as water quantity and quality. Even a secondary focus on conservation of natural areas and biodiversity would require assessments at the landscape scale to assess impacts of agricultural strategies on forests and species (Leach et al. 2012).
Strategies for Improving the Performance of Smallholder Agriculture
Three main types of strategies are evident in debates about how to increase agricultural productivity. The first depends mostly on purchased inputs, the second on enhancing ecological processes, and the third on a combination of the two. The first envisages a market-driven pathway to prosperity that takes key lessons from agricultural successes that have been achieved elsewhere based on a “Green Revolution” (GR) model. Modern agriculture, in this view, is based on production systems in which the market supplies the inputs (e.g., fertilizers, pesticides, fuel for traction and transport) and receives the outputs; the main performance measures are yield and income. The Green Revolution took the input-based trajectory to Asia and Latin America, achieving widespread increases in cereal yields through the use of improved varieties, fertilizers, and irrigation between 1960 and 2000 (Evenson and Gollin 2003). While it did not have a major impact in Africa during this period, there are current efforts to achieve a Green Revolution in Africa through improved access to inputs and markets (Toenniessen et al. 2008).
In the first-world context, organic agriculture is often seen as the alternative to industrial agriculture (Seufert et al. 2012; Pollan 2006; Bennett and Franzel 2009). The debate on the future of food and agriculture is polarized, and those with a stake in “real” (industrialized) agriculture have seen “sustainable” or “organic” agriculture as an enemy camp. This unconstructive stand-off may be easing as concerns about the economic and environmental costs of reliance on purchased inputs becomes more mainstream in both industrialized and developing country contexts. The term “sustainable intensification” is increasingly widely used (Pretty 2008; Pretty et al. 2011; Godfray et al. 2010; Tilman et al. 2011; http://www.feedthefuture.gov/). This term suggests the aims of reducing the environmental costs of agriculture in the industrialized world and increasing production in poor countries with a minimum of damage to the environment (Balmford et al. 2012). The term does not imply much about how these aims will be achieved or assessed, and perhaps this ambiguity is the basis of its popularity.
The term “agroecological intensification” (AEI) also implies a concern for sustainability, but it suggests a further commitment to intensification strategies that emphasize the use of biological processes to achieve this. Other authors have used “eco-efficient (p. 109) agriculture” (Keating et al., 2010) and “ecological intensification” (Doré et al. 2011) to refer to the same or a similar concept. The concept of AEI can be loosely and flexibly defined as producing more of what is wanted based on the efficient use of biological interactions. AEI entails the integration of diverse components to produce heterogeneous, multifunctional systems that are locally adapted. The principles of AEI include improving productivity under resource limitations; improving water and nutrient capture and cycling efficiency within the system; improvement of components to support systems functions; development of local, context-specific options; and adapting social institutions to support the use of biological interactions. The research frontiers of AEI include systems diversification; soil and water management; pest, weed, and disease management; and social innovation (including value chains) to support diversification.
In some systems, such as much of Asia’s irrigated ricelands, the major grain-producing areas of North America, and most intensive vegetable-production systems worldwide, productivity increases have been achieved through input intensification, with accompanying environmental costs and with declining returns on investment. In these systems, AEI would mean reducing the reliance on external inputs and increasing ecological efficiencies. Many other farming systems are on degenerative trajectories, with depletion and erosion of soil, water, and genetic resources. For these systems, AEI may require both ecological engineering and the selective use of purchased inputs. Ethiopia and Malawi, for example, have large rural poor populations that depend on agriculture. Agricultural productivity is constrained by degraded and unproductive soils. Government policy in both of these countries focuses on increasing fertilizer use, through subsidies and input supply. Detractors point out that the strategy is unsustainable, noting that alternative methods of maintaining soil fertility must be employed, such as the increased integration of leguminous crops. While the debate often seems polarized between voices advocating for one approach or the other, a hybrid approach could be regarded as the most pragmatic. The use of fertilizers can be critical for reversing a degenerative pathway. When soil fertility is too low, plant growth may not be sufficient to develop biomass for improving soil organic matter; such systems may require mineral fertilizers to allow legumes to thrive. That is, legumes can enrich the carbon and nitrogen content of soils and contribute to diets, but only if adequate P is supplied. At some point, the system may be on a sufficiently regenerative pathway so that lower input levels are effective.
There is mounting evidence to support the view that a combination of agroecological methods and judicious use of inputs is the most appropriate strategy for supporting the improved performance of smallholder agriculture. For instance, Snapp et al. (2010) found that the use of semi-perennial legumes together with modest quantities of mineral fertilizer was more effective and accessible for Malawian smallholders than the use of mineral fertilizers or legumes alone. Similarly, Vanek et al. (2010) found that phosphorous (P) fertilizer was required to support legume productivity in the Andes. Marenya and Barrett (2009) found that nitrogen fertilization was only cost-effective for Kenyan smallholders when soil carbon levels were adequate. When soil organic matter was too low, the increased maize yields associated with applied nitrogen fertilizer did not compensate for the cost of the fertilizer.
(p. 110) These examples illustrate the need to supply nutrients for many smallholder farming contexts, and they underline the point that maintaining healthy and productive soils involves more than supplying inorganic fertilizer. Soil organic matter must be maintained in order to support the efficient use of applied nutrients, as well as to hold water. Legumes can fix nitrogen and increase P availability, but only if their symbiotic relationships with microorganisms, as well as their pests and diseases, are effectively managed. In well-endowed farming contexts, organic agriculture often entails the massive import of nutrients into the system, typically in the form of high-quality manure, an asset not available to most resource-limited smallholder farmers. These issues are considered in greater detail below.
Examples and Evidence from AEI Frontiers
Managing Systems Diversity
Diversity has several potential functions within agroecosystems, including reducing risk (van Noordwijk et al. 1994), increasing productivity, and allowing for improved diets. In the context of well-endowed systems, these functions can be accomplished through the use of inputs and markets. Industrialized agricultural systems have favored monocultures, partly because these are easier to manage in mechanized systems, and partly because market efficiencies encourage specialization. Although the majority of calories produced through agriculture now come from just a few species, there is tremendous potential to diversify systems with the vast number of species and within-species diversity available. Crop and livestock diversity can be directly manipulated, with varying effects on systems productivity and stability. The diversity of farming systems includes the species intended by the farmer, as well as the associated diversity (life forms other than those planned by the farmer). Associated diversity can contribute to positive functions such as pollination and decomposition, or it can be harmful, as discussed in the section on pests below. The extent of associated diversity tends to correlate with the diversity that farmers implement (Vandermeer et al. 1998). Diversity can be handled in a range of ways, both temporally (simultaneous planting, overlapping life cycles, in series) and spatially (patch size, arrangements, segregation and integration at different scales). Options include intraspecific mixtures and multilines, intercrops, relay cropping (one crop goes in while the other is maturing), rotations, agroforestry and crop-livestock integration. A recent review summarized the various benefits and drawbacks of annual intercrops (Lithourgidis et al. 2011).
In studies of crop mixtures and intercrops, the more diverse systems typically outperform the corresponding monoculture systems. A range of mechanisms can contribute to the superior performance of polycultures. One mechanism is reduced competition, (p. 111) which leads to greater resource use efficiency, since interspecific or intervarietal competition is often lower than intraspecific competition. For example, there may be less root competition in mixtures, or less competition for light. Different crops or varieties may have different resource requirements, such as needing water at different times. The differing requirements of systems components can also mean that multiple components provide resilience. A given stress or shock may not affect all constituents equally, and those that survive can often compensate for those lost.
In addition to mechanisms related to competition and resource use efficiency, there is a set of mechanisms pertaining to facilitation, in which one species provides services to another through improved nutrient availability, water access, or pest protection. An obvious example of facilitation is nitrogen fixation by legumes, which can benefit associated cereal crops (Peoples et al. 2009). In countrywide assessments in Malawi, maize-legume rotations outperformed monoculture maize; pigeonpea (a semi-perennial legume) did particularly well (Snapp et al. 2010). Polycultures can contribute to improved nutrient use efficiency in other ways as well, for instance by contributing to increased P availability and to increased soil organic matter. More examples are noted below in the section on soil and water management. An additional set of mechanisms involves reduced losses due to insects, weeds, and pathogens (collectively considered “pests”). More on this range of mechanisms will be mentioned below, in the section on pest management.
Perennials can contribute special roles in polycultures. As illustrated by many successful examples of agroforestry systems, trees offer products and ecosystem services that other species cannot. Wood is obviously valued for fuel and construction material, and trees can provide fodder as well as protection from sun and wind. Trees and other perennials and semi-perennials have deeper roots that may be able to tap water and nutrients that are unavailable to other species (Cannell et al. 1996). This may smooth the impacts of weather variations, hence reducing risk. For example, enset (“false banana,” the starchy staple in risk-prone southwestern Ethiopia) can survive drought periods that would kill a cereal crop. Trees can reduce runoff, transpiration, and erosion (Ong et al. 2002). They can generate islands of beneficial soil biological activity (Pauli et al. 2010). On the down side, trees may compete with crops for nutrients and water. Trees are long-lived and, as such, involve inflexibility. Investments in agroforestry can thus take a long time to pay off. Because of the superior rooting systems that can be attained by perennial crops, there is some effort being invested in developing perennial varieties of certain annual crops, including rice, wheat, and maize (Cox et al. 2002).
Diversity and functional diversity are different things. That is, the number of species is not as important as the number of distinct functional traits, and not all combinations are created equal. In one study, for instance, fava bean responded well to mixtures with maize, but not with wheat (Fan et al. 2006). Components may interact in positive ways, but also in negative or neutral ways. Some interactions can be predicted, but others may result from idiosyncratic features, such as the way that a secondary metabolite from one species influences another. Successful systems may be developed based on trial and error and/or the use of ecological and process understanding. Although a great (p. 112) deal of theoretical and empirical effort has been dedicated to plant breeding, the formal research sector has invested a relatively paltry effort in optimizing functional diversity. Concepts, tools, and models of relevance to mixing species in cropping systems were recently reviewed (Malezieux et al. 2009); some of these points are mentioned below.
“Mimic hypotheses” suggest that benefits derive from system designs that resemble the conditions of natural systems in a given region, or that maintain the levels of diversity found in natural systems (van Noordwijk and Ong 1999). A recent review (Malezieux et al. 2009) noted the following principles for cropping systems design based on natural ecosystems mimicry: the use of complementary traits to ensure production and resilience; maintenance of soil fertility through soil cover; ensuring complementarity and avoidance of competition; management of pests through multiple trophic levels, biopesticides, and botanical properties; and the emulation of ecological succession processes after disturbance.
Because of the multiple functions of intercrops, some of which are only realized in the longer term, it can be difficult to assess and compare the merits of different systems empirically. Carberry et al. (1996) found that simulation using APSIM (the Agricultural Production Systems Simulator) was useful for exploring the performance of different farming systems over time and space. APSIM was also used to explore the effect of different cowpea growth habits (morphological traits) and row spacing in intercrops with maize in low-input production systems (Carberry et al. 2002). That said, the tools of systems agronomy are poorly developed with regard to multispecies systems (Malezieux et al. 2009), and this deficit includes the modeling tools.
Lack of dietary diversity is a major issue for too many smallholders. While the Green Revolution succeeded in increasing the availability of carbohydrate-based calories to millions of people in Asia and elsewhere, the production of legumes decreased as cereal production increased. In parts of the world where the Green Revolution had little impact, including most of Africa, diets are typically based on starchy staples such as maize, sorghum, millets, banana, and cassava. Protein-energy malnutrition is an issue in many places, but micronutrient malnutrition is much more widespread.
A simple case of diversification that has the potential to increase nutrition is the diversification of maize-based system with legumes (e.g., adding beans or other legumes in intercrops, relay crops, or rotations). This approach has shown success in improving nutrition in Malawi when coupled with strategies to ensure that child feeding practices and gender relations support the use of the legumes for improving child care and feeding (Bezner Kerr et al. 2008). This sort of strategy can be extended by including other crops or sets of crops that can contribute to ensuring the availability of diverse foods throughout the year (or crops that can be sold to allow the purchase of diverse foods, if markets and gender relations support this). Another approach is the use of small patches to produce diverse foods for household consumption; intensive kitchen gardens have been successful on a large scale for improving diets in Bangladesh and elsewhere (Bushamuka et al. 2005). This is feasible because input requirements (labor, imported nutrients, water) can be managed at the small scale needed to feed an individual family. Fruit trees are often a component of such home gardens.
(p. 113) The ecological principles of diversification complementarity, facilitation, and selection are relevant to agricultural diversification (Malezieux et al. 2009). Plant breeding can enhance all three, in addition to directly affecting component productivity. To enhance complementarity, plant breeders can design and select polyculture components for distinct and noncompetitive niches. To enhance facilitation, breeders can select for traits such as nitrogen fixation and chemical traits that provide benefits to other systems components. In implementing participatory breeding strategies, formal-sector breeders can provide surplus diversity to farmers, who then select the most adapted germplasm for their local conditions (Ceccarelli et al. 2009).
Varietal performance of crops grown alone does not always predict performance in an intercrop. In many intercropping studies, significant genotype-by-cropping system interactions have been detected. This implies that varieties need to be evaluated in the system in which they will be used (Gebeyehu et al. 2006). This is not, however, commonly appreciated or practiced by plant breeders. For example, although 97 percent of teff fields were integrated with oilseed crops in a study in Ethiopia (Geleta et al. 2002), teff breeders do not test the performance of teff varieties in combination with other crops. In some cases, legumes have been bred for intercropping, for instance to avoid shading their companion crops (e.g., cowpea; Singh et al. 1997).
Breeding for AEI performance could mean not only breeding for compatibility with other crops in a system, but also better capacity for symbiotic relationships with microbes that fix nitrogen (Mpepereki et al. 2000), help plants access phosphorus (mycorrhizae), or protect them from pathogens (endophytes or epiphytes). More conventional traits that can be considered part of AEI breeding would include breeding for nutrient use efficiency and pest and disease resistance. These are broad fields that are largely outside the scope of this chapter. From a nutritional perspective, AEI breeding would entail selection for multiple production traits: leaf and grain, food and forage, grain and green manure quality (human, animal, and soil nutrition are among the ecosystem services to be considered). Increasing nutrient content and availability (“biofortification”) is another active field of research.
Managing Pests and Diseases
Pests are major sources of systems inefficiencies in agriculture. Oerke (2005) estimated that ∼40 percent of crops are lost to insects, diseases, and weeds (collectively known as pests) on a global basis. In East and West Africa, where little pesticide is used in most smallholder production, losses were estimated at >50 percent. These losses would be considerably higher if crop protection actions were not taken.
In the chemical boom-years that followed World War II, pesticides were considered the answer to pest problems. Since then, a number of problems have emerged, including health problems, environmental damage, and boom-and-bust cycles (Devine & Furlong 2007; Williamson et al. 2008). In spite of the well-known downsides of pesticide use, however, this remains the dominant method for pest management in agriculture. (p. 114) Pesticide sales increased steadily between 1960 and 2004 (Oerke 2005). The concept of integrated pest management (IPM) arose in response to the widespread problems associated with chemical pesticides. IPM components include host plant resistance, cultural practices, repellent plants, natural enemies (natural and introduced), biopesticides, and the judicious use of synthetic pesticides. In some contexts, intensive IPM strategies can be successfully implemented in systems that inherently favor pests, such as monocultures of high-value horticultural crops or potato crops grown without rotation. In post–Green Revolution contexts in the developing world, successful IPM efforts have focused on integrating local farmer and research knowledge, knowledge transfer and learning, and collective action, often through the use of farmer field schools (Bentley 2009).
A focused IPM approach makes sense for highly destructive pests of high-value crops and main staples. Examples of the latter include Banana Xanthomonas wilt in East Africa, millet head miner in West Africa (Payne et al. 2011), rice blast in Asia, and late blight in potato in many regions of the world (Nelson et al. 2001). In many smallholder contexts, however, it is not feasible for farmers to deploy such intensive methods to deal with the diverse pest problems that afflict their systems (Orr 2003). Nor does conventional IPM make sense for various secondary pests of secondary crops. For such systems, it is more useful to implement diverse farming systems that are inherently more resilient with respect to pest population dynamics (Nelson 2010). For farmers with a range of crops and an assortment of constraints, it more often makes sense to focus on system health than on any particular problem.
Polycultures tend to have lower pest pressure than the corresponding pure stands. In a review of 209 studies involving crop mixtures, over half were found to have lower pest levels, while 15 percent had higher numbers of pests (Andow 1991). In a meta-analysis of plant diversification studies involving 552 experiments published in forty-five papers, diversity was found to reduce pests and damage overall, but also to incur a mean reduction in yield (Letourneau et al., 2011). Thus, while polycultures can outyield their corresponding monocultures, they do not inevitably do so, and some intercrops can actually increase pest pressure (B. Medvecky and J. Ojiem, personal communication). Polycultures can reduce pest pressures through a number of mechanisms, such as rotations, which can break pest cycles. For example, when Striga is a problem on cereals, rotations with nonhost legumes such as cowpea can cause “suicidal germination” (Oswald and Ransom 2001) of the parasitic weed, reducing the seed bank. In a mixture, there is a lower host density for a given pest. Nonhosts serve as barriers for pests looking for their hosts. Chemical ecology can be manipulated to disfavor pests in a variety of ways, attractant and repellent plants can be used to reduce pest damage, and plants can produce compounds that attract natural enemies of pests. Intraspecific diversity can be effective for pest management; varietal mixtures and multilines have been used extensively for management of crop diseases in particular (Wolfe 1985).
The push-pull system illustrates the potential of chemical ecology in pest management, as well as the potential of systems design to improve overall systems health and productivity. It also illustrates the vulnerability of a fixed-package approach. The stresses affecting maize yields in eastern and southern Africa include pests (principally (p. 115) the parasitic weed Striga and stemborers) as well as water and nutrient deficiencies. An intercropped legume (Desmodium uncinatum, which is considered a dangerous invasive weed in some countries) is dramatically antagonistic to Striga, while a border crop of Napier grass reduces the reproductive success of the stemborer. The economic viability of the approach is linked to the importance of the cut-and-carry livestock industry in the area, as well as to the importance of maize (De Groote et al. 2010; Khan et al. 2008). The value of the Napier grass component is high when (a) fodder is needed and (b) stemborers are a problem (De Groote et al. 2010). The value of Desmodium is high when Striga is a threat to maize production. In addition, Desmodium can also supplement Napier grass as a fodder. Local adaptation that maintains the key elements but varies detail is needed; this is already happening with extension to other cereals in western Kenya. The push-pull system’s stability has been challenged by a disease of Napier grass that threatens not only the push-pull system, but also the viability of the crop-livestock system of the region. It might be anticipated that pests of Desmondium will become a problem if planting becomes more widespread. A greater diversity of fodder crops is clearly needed, and alternatives to provide the functions of Desmodium would be particularly useful.
According to Oerke (2005), weeds alone have the potential to cause 34 percent losses in major crops worldwide. IPM strategies for weeds include improving herbicide use efficiency (minimizing chemical use), developing biological and mechanical methods (alternative curatives), and developing cultural or ecological methods (Bastiaans et al. 2008). Crop competitiveness can be increased by transplanting, seed priming, targeting fertilizers to crop rows, and breeding for traits like early vigor and allelopathy. Systems approaches have shifted the work of weed ecologists from a focus on the effects of weed competition on crop growth to a focus on influencing weed population dynamics and the longer-term development of weed populations (Kropff 2001). Approaches to reducing weed seed production include the use of weed-suppressive crop varieties, particularly those that compete effectively for light through vigorous early growth or those with allelopathic properties (Belz 2007).
While much of the literature on polycultures considers plot-level issues, it is acknowledged that higher scales are important as well. The concept of “ecoagriculture” involves the importance of managing agricultural landscapes in such a way as to conserve biodiversity, including wild species (Scherr & McNeely 2008). The diversity of noncultivated crops can benefit farmers, including through the availability of harvestable foods. Noncultivated areas in agricultural landscapes can provide refugia for natural enemies of crop pests. Spatially explicit modeling revealed the importance of non-crop habitats surrounding agricultural plots and their spatial arrangements relative to crop fields (Bianchi et al. 2010), underlining the relevance of information about natural enemies’ behavioral traits (e.g., ability to disperse, tendency to aggregate). Although aggregation of crop plots usually favors pest populations, the opposite was found for the Andean potato weevil: clustering potato fields is both traditional and effective in controlling this key pest (Parsa et al. 2011). A meta-analysis showed that the effects of landscape complexity on pest pressure were variable: in 45 percent of studies, landscape complexity (p. 116) reduced pest pressure, but no effect was seen in 40 percent of studies, and complexity increased pest pressure in 15 percent of studies.
Host genetic diversity can influence pathogen population structure, which can in turn affect disease epidemics. In an experimental study of the effect of landscape heterogeneity on the spread of wheat stripe rust, host frequency and the size of the initial epidemic focus were found to have significant effects on disease spread (Mundt et al. 2011). In a study involving joint analysis of three large, country-scale data sets on the wheat leaf rust epidemics in France, it was found that the extent to which specific varieties were cultivated affected the frequencies of the corresponding pathogen races, which in turn influenced the performance of varietal resistance. The results of both of these studies imply that greater varietal diversity will reduce epidemic pressure on a given host genotype, as expected.
Models can contribute to an understanding of plant disease epidemics and the roles of host resistance and diversity, pathogen population characteristics, and the environment (including farmers’ management options as they affect any of these). Modeling can provide insights on trade-offs in pest management. For instance, simulation has been used to explore the utility of various innovations and how they interact with farm types. The costs and benefits were found to vary with the type of farm (Blazy et al. 2009). In the Collaborative Crop Research Program’s (CCRP) Andean region, Rebaudo et al. (2011) are using agent-based, cellular automaton models to understand how decision making influences pest dynamics over time and space.
Plant breeding can make use of resistance at the gene, genotype, and population levels. Through the use of natural allelic diversity, conventional breeding can be effective at solving most pest and disease problems when well-resourced breeding programs apply well-designed strategies. Effective resistance breeding requires an understanding of the diversity of types of resistance genes and phenotypes available in crop biodiversity. Although breeding for forms of resistance governed by single dominant genes is relatively straightforward, it has often led to boom-and-bust cycles because insects and pathogens can rapidly evolve to overcome the resistance. For pest-disease systems with high evolutionary potential (McDonald and Linde 2002), breeding programs thus aim to accumulate multiple genes of small effect, which can be achieved by recurrent selection.
For some pests and diseases for which natural allelic variation for resistance is limited, it may be worthwhile and possible to seek genetically engineered forms of resistance. Many transgenic schemes have been designed for pest resistance, such as insect resistance through genes obtained from a bacterium (Bacillus thuringiensis, or Bt) and virus resistance (Marra et al. 2002). In sweetpotato, for example, weevils are a significant problem, and solutions have been sought in vain though conventional breeding, integrated management, and even pesticides. Given that sweetpotato is vegetatively propagated on small plots, it would be possible, in principle, to manage the pest through transgenic resistance provided by Bt genes without pollen contamination (through the use of nonflowering varieties) or excessive selection pressure for resistance build-up on pest populations (since sweetpotato is not grown in uniform monocultures). (p. 117) Sweetpotato and other vegetatively propagated crops are plagued by virus diseases that might also be effectively managed through transgenic resistance, allowing farmers to maintain high-quality planting material for longer periods (e.g., Kreuze et al. 2008). Thus, while transgenic crops are associated with limiting farmers’ seed-saving because of the notorious “terminator” technology, the technology can be utilized to support the opposite ends.
Many crops of importance in the developing world are not served by well-resourced breeding programs. Legumes have particular potential to improve soil fertility and human nutrition, but are they are particularly vulnerable to pests. Combining well-designed field-based breeding with participatory methods could go a long way to improving these programs. In addition, a strategic combination of molecular genetics and ecological genetics would enable more breeding programs to confront the specific pest challenges at hand (Salvaudon et al. 2008). Plants may be selected to attract pests’ natural enemies. Populations can be designed to incorporate functional diversity for pest resistance while maintaining the degree of agronomic uniformity desired for production, harvest, and processing.
Managing Soil and Water
Integrated soil fertility management is an area that is well researched and documented. Successful cases have shown evidence of increased productivity, better resource use efficiency, and reduced risk, among other effects. There is a range of aspects that can be combined through a stepwise approach, including integration of improved crop germplasm.
The success and limitations of conservation agriculture provide an encouraging and illustrative example of a significant transformation in production technology that has been widely adopted (and sometimes oversold). Crop cultivation is traditionally considered to be synonymous with tilling of the soil (Hobbs et al. 2008). Since the 1930s, various practices have been developed to reduce or eliminate tillage, to cover the soil with a permanent or semipermanent layer of mulch, and to practice rotation. This set of practices has matured into a set of systems, collectively termed “conservation agriculture” (CA), that employ broad principles (cover, reduce tillage, rotation) that contribute to maintenance of soil fertility in different ways in different contexts (Ekboir 2001). The application of the principles is endlessly variable, depending on the context.
CA has been transformative on vast areas, reducing costs and reducing soil erosion. As of 2009, over 100 million hectares were estimated to be grown under CA practices (Kassam et al. 2009). There has been little ideological divide on this—where it works, it is widely accepted. Its relevance is not universal, however, and the principles can fail in specific contexts (Giller et al. 2009). For example, when there is not enough available biomass to provide soil cover, or where there are better uses for available organic matter, it cannot be applied. Kassie et al. (2009) compared plot-level data on the use of reduced tillage and chemical fertilizer in two areas of Ethiopia. They found that reduced (p. 118) tillage was superior in the low-rainfall area of Tigray, where it was associated with lower production costs, higher production, and environmental benefits. In the higher rainfall area in the Amhara region, however, chemical fertilizer was much more profitable. This variability has implications for the adoption of CA practices by farmers, which has been patchy. Synthesis studies have failed to find common factors that explain adoption, except the need for practices to be profitable (Knowler and Bradshaw 2007; de Graaff et al. 2008). Thus, efforts to adapt and promote uptake of CA practices must be location specific.
Many projects promote the composting of crop residues to maintain soil fertility. This may well be preferable to some alternatives, but in Africa, a continent of negative nutrient balances (Cobo et al. 2010), it cannot be the complete answer. Some reported effects are very small, and many are extremely variable (Sileshi et al. 2010; Bastiaans 2008). This variability can be interpreted as unreliability, or as a risk for farmers and others. Legumes and other crops are known as “green manures” when they are grown and incorporated into the soil as nutrient sources for subsequent crops. A meta-analysis of green manures for maize, analyzing the results of fifty-two studies, showed a significant positive contribution to maize yields from woody and herbaceous green manures (Sileshi et al. 2010), though with huge variation in the results. This huge variation has important consequences for strategies to use the findings. While green manures improve soil fertility, farmers prefer multifunctional legumes to straight green manures (Amede 2003; Kikafunda 2003).
Water is a limiting resource for agriculture in many environments. Water scarcity creates one set of problems, and the damage caused by rainfall creates another; in particular, soil erosion is an important threat to sustainability in many systems. An increase in the frequency of destructive rain events is predicted for some areas as a feature of climate change. AEI approaches must confront these challenges. At the plot level, options include the use of drought-tolerant species and varieties, building soil carbon levels to enhance water retention, and the construction of strips and terraces to increase water infiltration and reduce runoff. Many of the options for water management must occur at higher levels, such as the watershed level.
AEI and Markets
Most government and donor initiatives emphasize market-driven development, with little emphasis on system health, sustainability, or better meeting the nutritional needs of rural households. To meet their various objectives, smallholder farmers can generally benefit from improved market access and better performance of input and output markets. But insofar as initiatives neglect issues such as risks induced by pests and climate, they may subject households to potential ecological, nutritional, and financial hazards. Approaches that consider markets to the exclusion of self-provisioning, agroecology to the exclusion of inputs and markets, or markets without concern for stability and sustainability will subject people to unnecessary risk. In keeping with the needs of farm (p. 119) families, it is important to balance concerns for short-term profitability with long-term sustainability, and to balance support for market-oriented production with the fulfillment of dietary diversity.
The example of the quinoa boom in the Andes illustrates the idea that markets need AEI. The international market for organic quinoa has provided Andean farmers with a lucrative market (Kimble-Evans 2003). Because the quinoa price is high, farmers have reduced or abandoned their traditional fallows to maximize their quinoa production, which has in turn led to soil degradation (Medrano Echalar and Torrico 2009; Jacobsen et al. 2011). Local quinoa consumption has declined, and it is likely that farmers sell it and purchase less nourishing foods such as rice and wheat noodles. The reduced following has led to a loss of soil fertility and a build-up of pests attacking quinoa. In desperation, some farmers have applied pesticides, the residues of which have been detected by buyers. This has threatened the viability of the organic markets. The failure to base the value chain on sound AEI production principles has thus threatened the system with nutritional, ecological, and economic collapse. It should be noted that this narrative is contested (Winkel et al. 2012) and that further analysis of Andean agroecology is needed to fully understand the ecological and market dynamics involved in quinoa production.
Examples illustrating the ways in which AEI needs markets would include seed systems, diversified markets that support of crop diversification, and biological control agents. As described above, one of the AEI research frontiers is crop improvement aimed at providing germplasm with traits such as greater resilience (e.g., drought and pest resistance, local adaptation) and improved performance in diversified cropping systems. Ensuring that farmers have access to seeds of the species and varieties that are likely to enhance the performance of their production systems is one area of innovation (e.g., Dorward 2007). Another AEI input market would be for biological control agents and biopesticides. For example, the millet head miner is a pest of pearl millet. A very effective biological control agent has been identified and implemented by a team of national researchers (Payne et al. 2011). For this effective and environmentally friendly pest management agent to be made widely and sustainably available to farmers, it will need to be commercialized. The challenge of reaching millions of resource-limited smallholders with eco-inputs such as biological control agents and other improved component technologies is a frontier of AEI. Building effective output markets that support crop diversification is another critical area needed to support AEI (Shiferaw et al. 2008; Lenné and Ward 2010).
Getting from Here to There: Making AEI Happen
Because contexts vary widely, AEI requires that strategies for local agricultural development be tailored to local needs, objectives, capacities, and opportunities. In view of agroecological and cultural diversity, this is a demanding proposition that requires a (p. 120) flexible approach to research and development. Although there is widespread agreement on the needs for greater agricultural efficiency and sustainability, several opportunities and obstacles to the widespread implementation of AEI approaches should be noted.
The scientific basis of AEI, including both the theory and the evidence base, needs further development. This provides an enormous opportunity for the biophysical and social sciences to contribute to a process of agricultural transformation. Most recent agricultural research has focused on developing the theory and empirical basis for industrial agriculture, leaving substantial space for the development of the AEI research base. Doré et al. (2010) highlight a set of approaches that hold promise for enriching the scientific basis for AEI. These include taking advantage of advances in the plant sciences in breeding crops that are more resilient in terms of resource use efficiency and resistance to biotic and abiotic stresses; using knowledge of natural ecosystems in the design of more efficient agricultural systems; using more sophisticated statistical analyses to understand how options interact with contexts, such as meta-analysis and comparative systems studies; and taking more effective advantage of farmers’ indigenous knowledge.
One set of constraints to AEI implementation has to do with the labor, time, and knowledge that may be required (Ruben 2001). The use of trees and legumes to build soil carbon, for instance, can take years. The input resource constraints may be absolute limitations, or they may be considered in relation to the risks entailed and the returns obtained (Ruben 2001). Measures aimed at reducing erosion can also be difficult and expensive to implement. Because such measures require investments of labor, time, and other resources, poverty and insecure land tenure can be obstacles to investments (Place 2009), such as those implied in AEI implementation.
A major challenge to the theory and practice of AEI is the inherent one of ecological diversity. African farming systems are, for example, notably diverse. Successful AEI will entail finding local “best fit” solutions to local problems and needs in a large number of environments. “Environment” here means not only the biophysical agricultural environment, but also the social, institutional, and economic context. For example, the viability of many options is known to depend on farmer resource endowment (e.g., Tittonell et al. 2010) and led to the development of the concept of socio-ecological niche for agricultural practices (Ojiem et al. 2006). Approaches based on the average performance across diverse environments and farmer resource endowments are not likely to perform particularly well in any given environment.
An important institutional constraint to identifying best-fit solutions to local production challenges and opportunities is that the policies and practices of national research systems that serve smallholder agricultural systems are oriented towards the production of sweeping prescriptions, such as blanket fertilizer recommendations made on a national scale. Farmers and researchers alike are aware of the enormous heterogeneity of soil conditions and the consequent absurdity of blanket recommendations. Even within a given farm, nutrient levels vary strongly among fields (Vanlauwe et al. 2006). An AEI approach would entail a change of strategy for national researchers, from a quest for “the mean” to an attempt to understand variability across environments and farmer types.
(p. 121) Although we stress the need for flexible strategies that respond to local conditions, most visible success stories related to AEI are more often presented as packages than as principles. There is a tendency for research and extension organizations to package, brand, and promote their technologies. Technology packages that utilize AEI principles include the push-pull (Khan et al. 2008) and conservation agriculture (Hobbs et al. 2008) systems mentioned above and the system of rice intensification discussed in “Alternative Paths to Food Security” by Norman Uphoff. While the these technologies are often seen and promoted as packages, they are also subject to centralized and local adaptation to respond to varying conditions and demands (e.g., integrating edible beans into the push-pull system, as described in Khan et al. 2009; tailoring of conservation agriculture to local contexts, as described in Ekboir 2001). It is important to develop strategies for technology promotion that support rather than suppress local innovation and adaptation.
Farm technology options must be suited to local conditions and adaptable to farmers’ varying circumstances, and farm systems must have the resilience needed to cope with the variability that occurs from season to season and from year to year. It is unlikely that a centralized approach could deliver these results, particularly when national research and extension systems are strapped for resources. These requirements and conditions imply the need for a local innovation capacity. There is a need for approaches that build the social structures needed for group problem-solving and resource mobilization. Examples of such approaches include farmer field schools that allow farmer groups to learn about and experiment with agroecological methods (Pretty 2003). “Innovation platforms” bring together producers with other players along value chains to enhance smallholder market access and improve the efficiencies of input and output markets. Nontraditional market approaches can support diversification, local value addition and responsible input use. An example of such an approach is the “community basket” movement in Ecuador, which brings together Andean smallholder farmers and low-income urban markets for mutual benefits of fair pricing and valuing of culturally significant crops.
Research should be focused on understanding principles and processes underpinning agroecology and developing suites of component technologies, as well as concepts and models for their local integration (e.g., Whitbread et al. 2010). The underlying theory and principles of AEI should be the subject of aggressive international research, but the specifics of their implementation need to be worked out locally. Traditional research and extension approaches that are oriented to developing general prescriptions have little relevance in view of the diversity of farmers’ conditions and requirements. There is a need to support local innovation processes through which communities and families can access, adapt, and integrate diverse options according to their particular objectives, problems, and opportunities.
We conclude with an endorsement of the call by Leach et al. (2012) for new technologies, new policies, and new modes of innovation. Smallholder farmers around the world need more ecologically efficient options that work under their resource constraints in their diverse social and biophysical contexts. We need policies and incentives that (p. 122) support researchers to work in new ways to support social and technical innovation at the local level.
This chapter is loosely based on a briefing paper commissioned by The McKnight Foundation and draws upon some experiences gained by the authors through their involvement with The McKnight Foundation Collaborative Crop Research Program (CCRP).
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