Prof. Timothy G. Reeves, Director General, CIMMYT

The only way for agriculture to keep pace with population and alleviate world hunger is to increase the intensity of production in those ecosystems that lend themselves to sustainable intensification while decreasing the intensity of production in the more fragile ecologies. In particular, if we fail to get agriculture moving in the African countries south of the Sahara, poverty will continue to grow, and the impending social upheavals that will ensue will become a global nightmare.

Borlaug and Dowswell (1997)

Contents

Introduction
Sustainable Agriculture: What Is It?
New Research Paradigms
The Practice of Sustainable Agricultural Systems
        Role of Genotype (G)
        The Role of Environment (E)
        The Role of Management (M)
        The Role of People (P)
Bringing It Together
Achieving Impacts
References
Acknowledgments

Introduction

Much has been said about the need for sustainable agriculture during the past one or two decades. Hardly a paper is written or a speech given on agriculture which does not now incorporate the word "sustainable." This level of awareness is indeed healthy because agricultural systems that are sustainable are not only desirable, but obligatory and urgently required. However, as Alexander (1992) put it so well, "Everybody wants sustainable agriculture, but few have any idea of what it actually means, let alone how to go about achieving it."

This challenge -to turn good ideas into reality- has been a continuing objective of agricultural science since its inception. However, the challenge of putting sustainable agricultural systems into place has perhaps seen less progress than is desired and indeed, necessary. The concept of sustainable agriculture is difficult to deal with in most countries, particularly in many developing countries, where farmers have few resources and little flexibility to change their practices, and where the risks of failure often have tragic consequences.

We have only to re-read Dr. Borlaug's statement above to understand that it is imperative that we as scientists "get real" in our work on agricultural sustainability. It is essential that ideas on sustainability move with appropriate urgency from scientists' and farmers' brains, to real research programs and real farmers' fields. It is a challenge being taken up by CIMMYT, with its partners, as we move into systems-based research, organized in multidisciplinary projects.

I believe that scientists and farmers have made real progress in some areas of agricultural sustainability. I am also highly optimistic that, with continued application and investment, there will be major developments in the next ten years or so, as biotechnology and other new tools are effectively utilized.

To achieve this accelerated development, however, new research paradigms are required. Such paradigms would effectively address whole systems; more effectively combine new technologies and traditional knowledge; and more effectively integrate farmers and communities into research, development, and extension. This paper first outlines a few important principles of sustainable agriculture and then takes a close look at some practical approaches that we can follow to make sustainable systems a reality in farmers' fields.

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Sustainable Agriculture: What Is It?

Sustainability in agriculture is a "moving target." No single method of farming in any region remains sustainable without continual intervention and change. Agriculture is based on dynamic biological, physical, and chemical systems, and farmers live in a constantly changing economic, social, and political environment. Given this scenario it is illogical to believe that there is a "magic bullet" to deliver sustainable agriculture to all farming locations. The reality is that sustainable farming systems can differ from field to field and from one period of time to another. What is sustainable in one place, at one time, may not be sustainable forever, which is why continued investments must be made in agricultural research and in updating farmers' knowledge and skills. The task is never finished; indeed, this is reflected in one of the dictionary definitions of "sustainable":

That is, to remain sustainable, an agricultural system must continually be supported with new knowledge, new practices, and new technology.

Whilst it is not surprising that such a complex topic as sustainability generates considerable debate and a range of widely differing opinions, the time has now come for consensus on the ways forward. Nero fiddling whilst Rome burnt, pales into insignificance compared to well-heeled experts in the North involved in never-ending academic "slanging matches" as 40,000 women, children, and men die each day in developing countries. We must move forward, and move forward collectively, each doing what we do best and putting our energies into integrating these efforts, rather than arguing as to why they are mutually exclusive, or one is right and one is wrong. Action is paramount!

One of the major recurring debates has focused on the level of inputs applicable to "sustainable agriculture." The fact of the matter is that for a system to maintain its sustainability, the nutrients and other components removed in harvested produce or lost in the production process must be replaced to maintain balance. Accordingly, it is reasonable to assume that a range of alternatives is available at the site level, but only some options will actually be sustainable (Table 1).

Table 1. Input/output levels and system sustainability

For the resource-poor farmer, who often has to produce more food from less land, the temptation to "mine" the land is overwhelming. Hence the perilously low levels of soil fertility in many regions of the world, particularly sub-Saharan Africa. Many farms have shifted inexorably from high input­high output systems (when land was first cleared and millennia of soil fertility were there to be tapped) to low-high systems, and now, on all too many farms, to low-low systems. Whilst one could argue that the latter type of system is in balance, it is not sustainable. It is almost invariably not productive enough, or profitable enough, for the farming family to enjoy a reasonable standard of living or even to survive. In addition the farmer is quite naturally continuously trying to extract a higher level of output from the farm than the low or zero level of inputs can sustain. This practice, born of necessity, results in a "downward spiral" of soil fertility. It gives the farmer no scope or flexibility for diversity or sustainable rotations, as the whole farm area is required to produce the basic foodstuff, be it maize, wheat, or any other food crop.

Interventions are necessary if this downward spiral is first to be halted and then reversed. Logically, one could argue that the interventions should be the return of the dung and urine of the humans and animals that ate the food produced from the field. At best, this is only a partial solution, as there are competing uses for animal dung, and there are social, health, and logistical issues in relation to human excreta. Whilst the return of animal dung and urine should be encouraged, other interventions are also necessary, and in many cases they will initially have to be external interventions. If we relied only on animal dung for the nitrogen needed for today's food crop, an extra 2.6 million cattle would be needed ­ creating an ecological disaster (Borlaug, pers. comm.). Inorganic fertilizers frequently are the most effective, efficient, and economical intervention, if available. Fertilizers not only produce more grain, but also more residues both above and below the ground, in the form of shoots and roots. These contribute more organic matter to the soil and enhance carbon and nitrogen cycling, which in turn results in even better production of crops and residues and initiates an "upward spiral" in soil fertility (Figure 1). As the downward spiral is reversed, the opportunities for diversification, biological nitrogen fixation, and rotations increase geometrically. The time to intervene and break the downward spiral is now, and methods to achieve this are described in detail later in this paper.

There are many definitions of sustainable agriculture; mine is not dissimilar to most of them, except in its inclusion of political supportability as one criterion. Sustainable farming systems should be:

• economically viable;
• environmentally sound;
• socially acceptable; and
• politically supportable.

Sustainable farming systems are economically viable at both the farm and national levels. At the farm level, the system must produce food and income, both now and in the future. Resource-poor farmers cannot invest in systems that will not produce reasonable yields and, even better, cash income over the operational period in question. Such returns meet immediate needs and may give farmers some opportunity to invest in farm improvements that will have more enduring benefits.

At the national level, agriculture must also earn its keep as a significant contributor to GDP and export earnings. Despite the grandest visions and wishes of politicians, the reality in most developing countries is that economic well-being and development are almost invariably based initially on productive and profitable agriculture, the "engine room" of subsequent industrialization.

Sustainable farming systems are environmentally sound. The need to maintain and enhance the economic returns from agriculture to developing countries, farmers, and rural communities has always been with us, but this need has probably never been of greater importance or fraught with greater uncertainty than it is today. But the complexity does not end there. As we have become increasingly aware in recent years, economic success must be achieved without unnecessary degradation of our soils, air, water, landscapes, and indigenous flora and fauna. Whilst most farmers claim to have always been cognizant of conservation issues, our greater understanding of the impact of land clearing, cultivation, overgrazing, and soil fertility changes has revealed that past intentions have differed significantly from reality. In many instances, through lack of knowledge and/or judgment, we have been profligate in our use of the basic resources of soil and water, and excessive cultivation has been one of the greatest threats to the sustainability of our soils.

The third facet of sustainable agriculture requires farming systems that are socially acceptable. In other words, these systems must be appropriate to the people who, relying on their own meager resources, are responsible for implementing and managing them. The need for socially acceptable systems implies the need for a better understanding of farmer and community needs and values, as well as better targeting of technology to meet local conditions.

The final facet of sustainable farming systems is really dependent on the first three. If economic growth brought about by agriculture can occur within an environmentally sound and socially acceptable framework, then politicians will continue to view agriculture as justifying their support. The power of political support and the impact of enabling and facilitating policies are paramount. On the input side of agriculture, policies can make a world of difference ­ for example, in establishing efficient systems for placing seed, fertilizer, and credit within the reach of farmers. The same is true after the crop is harvested, when pricing, transport, storage, and marketing policies strongly influence the economics of food crop production.

All four components combine to form the whole: sustainable agriculture. If one is neglected, it can seriously reduce the rate and extent of progress towards sustainability.

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New Research Paradigms

It is clear that if we as agriculturists are to make effective progress, we must change the way we plan, conduct, and communicate about research. Any component of a farming system can become the limiting factor to sustainability. It is therefore essential that those who work with farmers to develop sustainable systems are knowledgeable about the systems with which they work. This is not to say that everyone must be a generalist ­ far from it ­ but it is essential that highly skilled specialists such as breeders, pathologists, and socioeconomists understand the full context in which their interventions are made and the need for contributions by others. This implies a blending of research disciplines in teams of scientists seeking collective outcomes that are appropriate and have an immediate impact in farmers' fields. It is from these fields that food supplies must come for the foreseeable future, and the farmer is the ultimate systems-oriented operator, juggling biological, economic, environmental, and social factors. In such circumstances isolated interventions can usually be of only limited value.

To more readily develop integrated solutions to complex problems, CIMMYT has adopted a new research paradigm, based on:

Whilst each of these components of an agricultural system can produce significant improvements to sustainable intensification, it is their optimal combination on which the new green revolution will be based. Such a combination would consist of the best variety for a given environment, incorporated into an improved soil and grown using appropriate crop management, and both the technology and the desired outcomes would be appropriate to the farming people to whom it must be effectively delivered. This paradigm is indeed a bridge between a commodity focus and an ecoregional approach.

It is essential that all who seek to foster sustainable agriculture in developing countries recognize the interdependence of these factors, because most organizations individually cannot contribute fully to each component of GxExMxP. Partnerships and consortia that assemble the best possible teams to execute the GxExMxP paradigm will underpin the timely and successful achievement of sustainable farming systems. This has major ramifications for research and development institutions, both within and between institutions.

Many agricultural research institutions are not only structured by commodities and/or disciplines but conduct research, albeit high quality research, within these frameworks. This approach will no longer yield improvements in agricultural productivity at the rate that is urgently required. For it is not biotechnologists working alone, or plant breeders working alone, or physiologists, or agronomists alone, but their effective combination into multidisciplinary teams that will produce the desired results: beneficial impact in farmers' fields. Similarly, a straight commodity focus within, for example, a "wheat division" in an institution is unlikely to produce useful results in isolation. If a farmer has to grow wheat in a rice-wheat rotation, then it is logical that wheat researchers and rice researchers should work together to optimize the system, not each independent component of the system. The best wheat variety in a wheat-only research field may well not be the best wheat variety when it is sown late after a rice harvest ­ the farmer's practice.

The challenges faced within research institutions are similar to those faced between research institutions involved in the various facets of sustainable agriculture. Few organizations have the resources, skills, and knowledge to be the best at all facets of GxExMxP, but the achievement of sustainable agriculture is so urgent for the world that only the best will do. If sustainable intensification of agriculture in developing countries is to be achieved and maintained, institutions must be willing, and must have the organizational capacity, to form effective partnerships (North/South; public/private; research/development/extension/social; and their various combinations) to which they are enthusiastically committed. At CIMMYT we believe that some internal capacity in the various aspects of the GxExMxP paradigm is critical for us to partner other key institutions effectively. We have strengthened our resources in biotechnology, economics, and sociology to build a "credible mass" of scientists with whom outside agencies would wish to work. In addition we have established a Natural Resources Group, incorporating skills in crop and soil modeling, geographic information systems (GIS), and participatory research ­ disciplines broadly adaptable to all regions and aspects of CIMMYT's global maize and wheat research mandate. As a result of this approach, plus the introduction of a multidisciplinary project structure, we believe that CIMMYT is effectively positioned to achieve its organizational motto: "Sustainable maize and wheat systems for the resource-poor."

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The Practice of Sustainable
Agricultural Systems

The exact combination of optimal management and input factors can vary from field to field and farm to farm, and generally it will vary from region to region as biophysical and socioeconomic environments change. However, extensive experience around the world ­ North and South ­ strongly indicates that a number of practices are common to developing sustainable agricultural systems in many different situations. These practices include reduced tillage, nutrient management, rotations, integrated pest/disease/weed management, water use efficiency, and the use of appropriate and adapted crop/plant species/varieties.

Much has been written on these practices, but it is valuable to summarize their past and potential contribution to the GxExMxP research paradigm for sustainable agriculture.

Role of Genotype (G)

In feeding ourselves, are we starving our descendents? This is the question that has haunted the debate over agriculture's role in fortifying or depleting the resource base.

We believe that the answer to that question depends to a great extent on the kinds of plant varieties we develop and grow. If we set our crop breeding priorities wisely, we can develop genotypes that contribute ­ directly and indirectly ­ to sustaining the resource base.¹ These are the genotypes that will help make the GxExMxP equation truly powerful.

Two ways that genotypes can contribute ­ and have contributed ­ to conserving natural resources is through their effect on biodiversity and the stability of production. Several examples, drawn from the research of CIMMYT and its partners, are given here.

Pedigree diversity in wheat ­ The advantages that genetic diversity brings to a farmers' field are numerous. They include the capacity ­ hidden in the seed ­ to protect against unexpected threats, such as a new disease. This protection increases the stability of agriculture and reduces risk.

Since the early days of the Green Revolution, greater numbers of wheat varieties have been released, and many of these varieties are also more genetically diverse. As a result, genetic diversity on the farm has generally widened. Recent evidence suggests that the bread wheats that have been most widely adopted in the fields of developing country farmers also possess some of the most complex pedigrees (Smale and McBride 1996). The top ten wheat crosses grown in the developing world in 1990 are genetic powerhouses. They contain an average of 44 landraces, 19 generations, and 1,192 parental combinations in their pedigrees, of which about 20% were used only once. (For the sake of comparison, note that for all of the different crosses grown in the developing world in 1990, the average number of distinct landraces per pedigree is 36.) This gives some idea of the considerable ­ and continuing ­ investment made by farmers (landraces) and by scientific plant breeders (generations and parental combinations) in the diversity of the world's bread wheat crop.

This diversity offers additional protection against the vagaries of nature and supplements efforts by plant breeders to combat the biotic and abiotic stresses that can transform a farmer's crop from an asset to a liability in a matter of days.

Durable disease resistance ­ As Byerlee (1994) has observed, one of the most underestimated ways that improved genotypes contribute to sustainability is their superior disease resistance. Improved disease resistance increases yield stability and reduces the use of pesticides, some of which are the most environmentally toxic chemicals in existence. In most of the developing world, pesticide use on wheat has been minimal, and superior disease resistance has generally substituted for the fungicides that are widely used on wheat in industrialized countries.

All of the bread wheats developed by CIMMYT possess durable resistance to stem and leaf rust (Figure 2) ­ traditionally two of the most damaging diseases of wheat throughout the world. CIMMYT's strategy for breeding host-plant resistance to wheat rusts is to accumulate genes from diverse sources. The geographic origins of these sources are broad, extending from North and East Africa to Europe, North and South America, Australia, and New Zealand (Smale and McBride 1996).

Nitrogen use efficiency in wheat ­ Not all of the threats to stable and sustainable yields are living organisms such as disease pathogens. Genotypes can improve the resilience of the farming system if they are bred to use resources such as soil nutrients more efficiently, and if they can tolerate abiotic stresses such as nutrient deficiencies and toxicities or drought and its accompanying problems. The potential for such germplasm to reduce input use and production costs is considerable.

CIMMYT has analyzed the input efficiency of its old and new wheat genotypes under a range of nitrogen levels, moisture regimes, and weed conditions (Figure 3). Successive varieties developed by CIMMYT and its partners, which have been grown widely in developing countries, have required less and less land and nitrogen to produce the same amount of wheat (Figure 4). Varieties developed from CIMMYT wheats can reduce the chances that too much nitrogen will be used and can also make land available for alternative uses (Smale and McBride 1996). By reducing the use of nitrogen, we can also reduce the risk that this nutrient is lost in the form of air and water pollution.

Low nitrogen/drought tolerance in maize­ Maize is also being bred to withstand hostile and unpredictable production environments (CIMMYT 1997).² In marginal production zones, especially in southern Africa, farmers need to make the most of two extremely scarce resources: water and nitrogen. These farmers, who harvest increasingly meager crops from increasingly depleted soils, and harvest nothing at all when the rains fail, are the victims of the downward spiral mentioned earlier. We have taken many steps toward helping these farmers and others in developing countries; a few of the most important steps include:

• A proven methodology for obtaining a 25-40% increase in maize yields under severe drought, with no yield penalty under good conditions. We have also discovered that selecting maize under drought confers tolerance to low nitrogen conditions.
• A global development, testing, and distribution network for maize that tolerates drought and low nitrogen.
• More than 30 elite inbred lines of tropical or subtropical adaptation that resist drought or infertile (and acid) soils, as well as insect pests, and that provide outstanding yields in hybrid combinations.
• Progress in applying molecular markers to transfer resistance traits to elite maize lines and varieties.

Like the wheat varieties described earlier, these maize genotypes contribute to sustainable agriculture by increasing yield stability, reducing the inputs needed to obtain satisfactory yields, and ensuring that repeated drought does not leave land bare ­ the precursor to erosion and desertification.

Acid soil tolerance in maize and wheat ­ Large areas of acid soils in developing countries are poorly suited for agriculture, but the development of new genotypes has made it possible for farmers to put these infertile soils to profitable use. In the case of maize, for example, researchers in Colombia and Peru have released Sikuani V-110, an acid tolerant variety developed from CIMMYT materials that yields more than 30% more than local checks on acid soils. This variety is already sown on at least 15,000 hectares. Because of new germplasm such as this, fewer farmers will be driven to open new land for agriculture after exhausting the limited potential of the land they already farm.

Summary ­ Appropriate varieties of maize and wheat do more than foster food security: they provide real environmental payoffs. A key aspect of improved crop varieties is that they are "embodied technologies"; they deliver sustainability in the seed. Simply by sowing the seed of a new variety, a farmer adopts the improvements that have been incorporated into it, such as better yield, enhanced nutritional quality, improved disease resistance and stress tolerance, and enhanced competition with weeds.

The probability of success may be greatest in breeding for tolerance to biotic stresses (Table 2), but as we have seen, breeders are making good progress on all fronts. Biotechnology offers even more exciting prospects for delivering germplasm that contributes to a more sustainable agriculture.

Table 2. Prospects for developing specific traits compatible
with sustainable systems, through plant breeding

Source: Francis (1993).

The direct contribution of improved genotypes to sustainable agriculture has been large and is easy to appreciate: higher yields with fewer inputs at less cost to the environment. However, as Byerlee (1994) has pointed out, often the most important contributions of superior maize and wheat varieties are indirect, and they are largely unrecognized in the sustainability debate:

• land-saving increases in productivity;
• poverty alleviation;
• productivity increases in favorable areas that alleviate pressure to migrate to more marginal (and often more fragile) environments (Harrington 1993); and
• productivity increases in favored areas that benefit the poor in marginal areas through lower food prices and greater employment opportunities.

These are powerful achievements, but it is instructive to remember that promising new seeds are not grown in isolation: they are grown in real places, by real people. We turn our attention next to the role of the environment in the GxExMxP paradigm.

The Role of Environment (E)

Crop varieties can be replaced by farmers. However, the environments in which those varieties are grown are pretty much fixed. Important environmental variables include maximum and minimum temperature, elevation, precipitation, potential evapotranspiration, solar radiation, day length, soil pH, and other soils characteristics. What cannot be changed at least must be understood: CIMMYT is making an increased effort to understand and characterize maize and wheat production environments. Over the past couple of years, we have strengthened our capacity to conduct spatial analysis of these environments through a major renewal of our GIS laboratory. This renewal includes new hardware, new software, new datasets, new staff, and new collaborative links with both South and North.

Within the GxExMxP paradigm, an understanding of the environment factor (E) is important in addressing sustainability problems. For example, soil erosion problems are easier to solve if we know where they are concentrated. Research on management of acid soils is best guided by a knowledge of where these soils are located and what they are like, chemically and physically. And research on managing drought must be based on an understanding of what is meant by "drought," which areas are affected, with what frequency, and with what consequences. CIMMYT's GIS laboratory recently finished, in collaboration with CIMMYT regional staff and national program scientists in southern Africa, an environmental characterization that helped define drought, plot its incidence and frequency, and select representative research sites for a new project aimed at developing drought-tolerant maize varieties (publication in process).

Characterization of maize and wheat production environments is needed if we are to understand sustainability challenges and to target possible solutions: new varieties and improved crop, system, and resource management practices.

It is well known that the relative performance of a genotype can vary over environments. A variety that performs very well in one environment may perform poorly in one that is dissimilar (e.g., DeLacy et al. 1994). CIMMYT's Natural Resources Group is working with the Center's Maize and Wheat Programs to define "megaenvironments" areas that cut across countries (even continents) and that have environmental characteristics similar enough to guide crop improvement. For example, CIMMYT breeders maintain that a particular kind of wheat germplasm is needed for a production environment with a mean temperature in the coolest month of over 17.5C and lying "primarily" between 23 N and 23 S latitudes at elevations below 1,000 m. The tools of GIS are being used to help identify where in the world these conditions are prevalent in wheat systems, and which wheat research sites in which countries are most representative.

The use of megaenvironments to guide plant breeding is spatial analysis at a broad scale. However, spatial analysis also can be used at narrower scales. For example, adaptation zones for individual cultivars can be mapped out by using crop simulation models combined with GIS (e.g., Chapman and Barreto 1994). Spatial analysis of production environments can do more than evaluate germplasm adaptation. When combined with simulation modeling it also can help target sustainable crop and system management practices to defined regions. CIMMYT's Natural Resources Group is embarking on a new project to identify those areas in Mexico and Central America best suited to sustainable maize technologies, such as green manures and conservation tillage. Efforts at adaptive and participatory research then can be targeted towards geographical areas where the technologies are biophysically well adapted and can be expected to perform well (White and Hartkamp 1998).

Similarly, simulation modeling is being used in research on risk management in drought-prone maize systems in southern Africa. Models are used to evaluate the performance of sustainable soil fertility management practices under a wide range of climate and soils conditions. Then GIS is used to see where these conditions are found (Harrington 1997).

Finally, spatial analysis of production environments can be used to add value to on-going site-level research on sustainable practices. Site similarity studies (see, for example, Hodson, Wall, and White, forthcoming) can identify other areas within a country, in a region or even on the other side of the world that are environmentally similar to a given research site. This helps research teams from different sites coordinate the sharing of information and gets them to think about possible extrapolation of research results. Of course, this requires that important research sites be environmentally characterized (for example, with daily temperature, rainfall, and solar radiation data).

In the past, spatial analysis of production environments has been used to make sense at the national level of research on soil fertility (e.g., Benson 1996); identify possible areas for the introduction of new crops (e.g., Myers 1994); track land degradation in hillside systems (e.g., Pachico, Ashby, and Sanint 1994); and even organize information for setting national agricultural research priorities (e.g., Pardey and Wood 1991). It is a critical part of the GxExMxP paradigm.

The Role of Management (M)

The implementation of improved management practices on farms is likely to make the biggest contribution to agricultural sustainability during the coming decade. When combined with robust, highly productive crop varieties, it is not uncommon for such systems to double yields in farmers' fields. Dr. Borlaug (pers. comm.) has indicated that, in his current work for Sasakawa-Global 2000 in Africa, the combination of CIMMYT-derived maize germplasm with fertilizer and timely seeding and weeding has usually doubled farmers' maize yields and in some cases has resulted in increases of 200-300%. The recent maize harvests in Ethiopia have been testimony to the powerful impact of this GxM combination.

It is therefore extremely surprising that many institutions have reduced the emphasis given to agronomy research. Even in some quarters of the Consultative Group for International Agricultural Research (CGIAR) there is a misguided belief that agronomy is not strategic research and can be left to others. This is not so. Strategic partnerships in "cutting edge" approaches to crop agronomy are as important as the alliances that are quite correctly being sought and established in biotechnology. Agronomy is no longer just about "spray and weigh" or white pegs in fields, although these are still some of the basic tools for certain kinds of agronomy research (impact in farmers' fields after all usually requires action in farmers' fields).

Strategic agronomy now involves a complex iteration of field studies, crop and soil modeling, the use of GIS, and remote sensing. The knowledge, skills, and resources required for effective, modern management research are just as significant as those necessary for biotechnology. Many aspects of agronomy and crop management can contribute to sustainable intensification of farming systems. In this paper, five key interventions are highlighted, as these interventions will be the foundation for sustainable agriculture in many parts of the world. They are:

• Crop nutrition: nutrient auditing and strategic fertilizer use.
• Soil organic matter: appropriate replenishment strategies, including green manures, crop residues, and agroforestry.
• Crop rotations: enhancing diversity, improving biological nitrogen fixation, serving as break crops to reduce pest problems, and allowing livestock to be integrated into the cropping system.
• Soil tillage: the critical role of reduced tillage and practical options for farmers.
• Integrated pest/weed management: the integration of resistant varieties with rotation; minimal pesticide use; role of competitive cultivars.

Crop nutrition ­ One of the greatest contributions to sustainability can be made by one of the simplest management interventions: the use of fertilizer to increase crop yields and enhance soil organic carbon and nitrogen cycling. Current levels of fertilizer use vary greatly between regions of the developing world (Table 3) and are particularly low in sub-Saharan Africa. An initial intervention to raise fertilizer applications can allow basic food grains to be produced on a smaller area of the farm, thereby providing some scope and flexibility for a farmer to adopt a rotation, green manuring, or some other treatment for replenishing soil fertility on the released land. Whilst there are well-recorded dangers of overuse of fertilizers (most of them in highly industrialized countries), the rates likely to be appropriate for use in developing countries are often an order of magnitude lower: 50 kg/ha in the South, for example, versus 500 kg/ha in the North!

Table 3. Average fertilizer use in developing countries

Note: 1988/89 data.

Fertilizer use does however significantly increase economic risks for the resource-poor farmer, so it is imperative that this risk be minimized by combining strategic fertilizer use with nutrient-efficient crop cultivars.

For both economic and ecological reasons, fertilizers should be used efficiently. This helps the farmer as well as the environment. Research by CIMMYT scientists has led to several means of improving fertilizer use efficiency. Our Maize Program has found that some maize varieties use nitrogen fertilizer more efficiently than others. Interestingly, these same varieties also appear to be more drought-tolerant (Edmeades et al. 1997). In Africa, research conducted by a CIMMYT-coordinated Soil Fertility Network has found that fertilizer use efficiency often can be improved by combining organic with inorganic fertilizers (Kumwenda et al. 1996). CIMMYT scientists also have found that substantial improvements in fertilizer use efficiency are feasible in rice-wheat systems in the Indo-Gangetic Plains. Helpful practices include timely sowing made possible through conservation tillage practices (Hobbs, Ortiz-Monasterio, and Sayre 1998, forthcoming), delayed fertilizer application (Ortiz-Monasterio et al. 1994), and the use of furrow and ridge irrigation (Sayre and Moreno 1997). This means that fertilizer application rates can be slashed with no sacrifice of yields but less environmental pollution. In many areas of the world, however, fertilizers are priced out of the reach of those farmers growing foodgrains and are used only on high value crops such as coffee or tobacco. High prices may be the result of high marketing margins or merely of distorting government policies. The CIMMYT Economics Program has assessed the effects of these and other factors on the farm-level attractiveness of fertilizer use (e.g., Harrington 1987; Heisey and Mwangi 1996; Mwangi 1996). All too often, unfortunately, the consequence is that farmers do not have a chance to try intensification strategies. So extensification runs rampant, with marginal environments falling to the plow and forests to the axe.

Soil organic matter (SOM) ­ Organic matter makes soil fertile, and in most situations increased SOM will help develop and maintain sustainable agricultural systems. However, efforts to increase SOM generally require considerable time, labor, and opportunity costs, and they cannot be readily achieved in the short term. For these reasons it is likely that at first many farmers will need to rely on a combination of inorganic and organic sources of soil nutrients to improve soil quality. Soil organic matter is easily lost through excessive cultivation, continuous cereal cropping, and the removal of crop residues, and it is imperative that attempts to increase SOM are maximized through complementary management practices. In the Rice-Wheat Consortium for the Indo-Gangetic Plains, for example, loss of SOM over time is thought to be one factor behind declining factor productivity (Bronson and Hobbs 1997). Diagnostic survey results suggest that farmers agree with this assessment and reveal the changes in farm system management over the last decade or so that are driving SOM changes (e.g., Harrington et al. 1993). Collaborative work is underway to define for rice-wheat systems the biophysical processes at work in SOM changes over time. This research has objectives similar to those of earlier (and highly successful) research on SOM changes in continuous rice systems (see Cassman et al. 1994).

CIMMYT, along with other Consortium members, is committed to helping develop new tillage, crop establishment, rotation, and crop residue management practices that can turn around this problem. CIMMYT researchers in other continents are also actively engaged in research to help improve SOM in major maize or wheat systems through the Soil Fertility Network in southern Africa (Waddington 1991), for example, and through the Central American Maize Program (Bolaños 1995).

Crop rotations ­ Suitable crop rotations can go a long way towards fostering sustainability in maize or wheat systems. Here, "rotations" are understood to include crop sequences, intercropping, relay cropping, mixed cropping, and agroforestry systems.

When a cereal crop such as maize is grown over and over again, a build-up of pests, diseases, or weeds can readily occur. In southern Mindanao, for example, maize-maize (and even maize-maize-maize) systems are known to suffer from severe infestations of weeds, especially Rottboellia spp. (Harrington et al. 1991). Continuous cereal cropping also may lead to reduced levels of soil fertility. In the Indo-Gangetic Plains of South Asia, CIMMYT-led diagnostic surveys found that continuous rice-wheat systems are inclined to have more problems with soil fertility than systems that feature an occasional legume, pulse, or sugarcane crop (Fujisaka, Harrington, and Hobbs 1994).

Agroecosystems that feature a diversity of species tend to be more resilient, better able to cope with biotic and abiotic stress, and (relatively) self-regulating (Altieri et al. 1987). This is because diverse systems feature multiple pathways for the flow of energy and nutrients into the system, and because other species often can compensate when one species runs into trouble. Agroecosystem diversity is important, even if diversity is not found in the same field. Farmers in drought-prone areas may grow both maize and sorghum (in different fields), knowing that they can benefit from higher maize productivity and value in relatively good years but relying on sorghum's greater drought tolerance in relatively bad years.

CIMMYT researchers in collaboration with partners from national agricultural research systems (NARSs) and non-governmental organizations (NGOs) are working in many regions on crop rotation/system diversification strategies to improve system productivity and sustainability. Many of these strategies involve insertion of green manure cover crops or other legumes in maize systems, such as Mucuna and Canavalia in maize systems in Central America (Bolaños 1995) and southern Mexico (Buckles and Barreto 1996); and groundnuts, pigeon pea, and Mucuna in maize systems in southern Africa (Waddington 1997). This collaborative work is not restricted to maize: similar work on diversification of wheat systems is also underway in Bolivia, Bangladesh, and in rice-wheat systems in the Indo-Gangetic Plains.

CIMMYT may be a maize and wheat improvement center but that does not mean we do not value the contributions of other species in diversified systems.

Soil tillage ­ New conservation tillage and residue management practices are among the most exciting options available today to improve the productivity and sustainability of maize and wheat systems around the world. And CIMMYT, together with its research partners, is in the forefront of much of this research.

All too often, conventional tillage in rainfed maize and wheat systems leads to a host of problems. The kinetic energy of rainfall on unprotected soil leads to erosion and soil fertility loss and often to a sealing of the soil surface. This sealing process typically results in increased run-off and reduced infiltration of moisture into the soil profile. Two valuable resources soil and water are thus wasted (three, if one counts the energy invested in the tillage practices themselves). Excessive tillage also accelerates the process of SOM loss and, in some systems, can badly delay crop establishment, leading to reduced yields, low water and fertilizer use efficiency, and continued pressures towards extensification of farming.

CIMMYT's collaborative research shows that various conservation tillage and residue management practices can ameliorate many of the problems described above. Even a relatively light crop mulch cover has been shown to reduce erosion and crusting, improve water use efficiency, and dramatically improve crop yields, both in maize systems (Scopel 1998) and wheat systems (Wall 1994). In rice-wheat systems in South Asia, zero and reduced tillage practices of various kinds raise yields (through more timely sowing), slash production costs, and boost water and nutrient use efficiency (Hobbs and Morris 1996).

In some instances farmers are immensely enthusiastic about conservation tillage practices, seeing them as a way to transform their cropping systems. This happened in the past with zero tillage practices on hillside maize systems in the Guaymango area of El Salvador (Sain and Barreto 1997), and it appears to be happening now with surface seeding and with zero and reduced tillage practices for establishing wheat after rice in the Indo-Gangetic Plains. However, there are other areas where current versions of conservation tillage practices may be less attractive, their numerous benefits notwithstanding. This often happens when crop residues are important sources of livestock feed (Erenstein 1997).

It must be noted that conservation tillage systems often lead to problems with weeds (Edwards 1987). The usual solution is to use herbicides. All too often, these herbicides are misused with what may be substantial costs to farmer well-being and public health. These costs need to be quantified, and conservation tillage practices developed that rely less on these inputs.

Integrated pest/weed management (IPM/IWM) ­ Excess pesticide use can be addressed through IPM/IWM programs. This technology is used widely in developed countries and is gaining greater acceptance in the South. Integrated pest and weed management is often cited as one of the pillars of sustainable agriculture because it is based on sound biological principles: a multifaceted approach to pest and weed management usually makes both economic and environmental sense and is less likely to lead to the development of resistance in the target pests.

However, IPM is knowledge-intensive technology, and such technology is often difficult for resource-poor farmers to adopt. There are many "What if?" questions to be answered in adopting IPM successfully, and unless these answers are readily available, at the time when the farmer has to make a decision, losses will occur, or the farmer may place undue emphasis on chemical control. CIMMYT is therefore working to simplify IPM procedures by embodying as much of the IPM technology as possible in varieties with genetic resistances and tolerances. Emphasis on host-plant resistance/tolerance to major diseases, pests, and weeds provides the farmer with a "buffer" in his or her IPM program, through the adoption of a much simpler technology: a new variety.

Some of the successes of this approach have already been described in the section on genotype. However, even in the most successful cases of host-plant resistance, such as durable leaf rust resistance in wheat, it is essential to combine resistance with other IPM strategies. For example, CIMMYT seeks to integrate its work on pedigree diversity in wheat with other work on varietal diversity and system diversity in farmers' fields. Simply put, we seek to have many genetically broad-based varieties grown in farming systems that are diversified with other crops and enterprises. This, of course, means partnerships with others who work on the various facets of the system.

Whilst much has been written on crop varieties with good resistance to pests and diseases, less is known about varietal tolerance to weeds, which remains a poorly exploited component of IPM (or IWM, to be more specific). However, as shown in Figure 4 (p. 13), CIMMYT varieties through their enhanced efficiency are more effective in tolerating weeds than old varieties. However, if one actually selects for weed tolerance some spectacular results have been obtained. For example, Reeves et al. (1993) showed that at a similar level of weed infestation the most competitive wheat cultivars had no yield loss from weeds, whereas the least competitive lines had yield losses of 20-40%. Given the development of weeds (e.g., Phalaris minor) resistant to herbicides in the rice-wheat systems of the Indo-Gangetic Plains (Malik et al. 1995) and elsewhere (Mexico, for example; see Sayre 1998), there is an urgent need for more support to develop competitive cultivars in all crop species.

Last, but by no means least, the complexity of IPM/IWM systems means that they are not easy to manage at "arm's length." For resource-poor farmers with limited or no access to remote communication centers, a "hands-on," community-centered approach is essential to provide timely and appropriate advice. Often NGOs are the most appropriate agencies to adapt and deliver such advice, and this is another clear example of the need for partnerships between those who develop, and those who deliver and adopt, sustainable agricultural systems.

The Role of People (P)

It is people who must implement and adopt sustainable agriculture, and it is people who CIMMYT and others seek to help. It is therefore somewhat strange that the role of people in developing, refining, and implementing sustainable agricultural technologies has often been overlooked. Many of the formal priority setting systems for sustainable research have not tapped the knowledge of farmers, or at best have done so only late in the process when farmers are often asked to adopt some technology that they may not consider very appropriate for their needs. If sustainability is to be a reality, far greater emphasis must be given to an effective combination of farmers' traditional knowledge with the contributions of science.

There may be significant cultural and social issues to consider when accessing information from farmers, but none are insurmountable. Farmers the world over are generally conservative, risk-averse individuals who are most comfortable in their own environment. For this reason, it is essential that farmers' contributions are solicited in a way that addresses their needs, values, and objectives. People's sense of "ownership" of new technology is critical if we are to progress rapidly from research to adoption and impact. Just as sustainable agriculture requires a new research paradigm, it also requires a new paradigm for involving people the research-adoption continuum (Reeves 1987).

In this continuum, which is depicted in Figure 5, all key partners have a role in the process from priority setting to adoption. Of course the contributions of groups throughout the continuum vary (represented by bold letters in the figure) as the emphasis switches from research to extension to adoption. It is important to note however that all partners are involved in priority setting, planning, and deciding what should be done. If you wish to know what farmers need, why not talk to them? They can often be instrumental in finding an appropriate way forward.

One example of farmer participation in research is a collaborative project between CIMMYT and Mexico's Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias (INIFAP). The project, which focuses on small-scale farmers in the Central Valleys of Oaxaca, seeks to assess whether collaborative breeding by farmers and researchers can increase farmers' welfare while maintaining or enhancing genetic diversity.

Throughout this region we have collected 152 maize samples that are representative of the variation in local maize landraces. The farmers who donated these landraces were interviewed about their perceptions of the positive and negative traits of the landraces, as well as their uses. The positive characteristics cited most frequently were associated with consumption, such as taste and suitability for special preparations. Other valued characteristics included good yield and short duration in the field. The negative traits cited most frequently were related to low yield and poor storage. The farmers identified 11 uses for their maize, including eight special preparations. The importance of consumption characteristics and the high number of uses suggests that home consumption of maize is an important concern for these farmers, and highlights the cultural importance of maize in the region.

Trials were established with the 152 samples, 17 historical accessions from the CIMMYT and INIFAP germplasm banks, and one improved population of the local landrace, for a total of 170 maize populations. Agronomic measurements were recorded for each population. Farmers from the region were invited to evaluate the 170 populations at physiological maturity and harvest. At harvest, 216 farmers (117 women and 99 men) came to evaluate the materials. The farmers' choices and the agronomic data have been combined, and the maize samples that were of most interest to the farmers were identified. Some samples were chosen more frequently by females, and others by males, whereas a few samples were important to both groups of farmers. These populations will be the basis for future breeding efforts.

An interesting outcome of this work is that the maize population chosen most frequently by women farmers yielded the least under trial conditions. This finding emphasizes the importance that women place on criteria other than yield. We are currently investigating the specific criteria used by men and women and relating these criteria to their specific socioeconomic and cultural characteristics. These results are still preliminary, and future research will be modified based on what we learn in the process, but it is already clear that farmers' role in this research is invaluable.

In many NARSs, both North and South, the lack of effective communication with farmers is still a major weakness. To make matters worse, investment in formal, government extension services has declined even more sharply than the investment in research. As disturbing as this trend may be, it has opened new opportunities in some parts of the world for systems that are proving to be particularly effective. The defining trait of these new successes is that they are "farmer-driven." For example, more than 40% of Australia's farmers belong to the LandCare movement. The movement comprises community-based farmer groups who identify their own issues and priorities and then seek appropriate assistance from researchers, industry, and other farmers in identifying and implementing solutions. Increasingly, funding support is moving from government extension services to these dynamic farmer groups. Whilst examples from the North are not always appropriate to the South (and vice-versa), farmers' control of their own destinies in relation to technology adoption is fundamental to further progress.

Many other examples of such an approach can be cited, but the general principle for the adoption of the new GxExMxP paradigm is involvement of partners throughout the research-adoption continuum. People and Partnerships, the title of CIMMYT's new Medium Term Plan, describes our focus on the people we seek to help and the partnerships necessary to do so. Sustainable agriculture will not be a reality unless people from all parts of this continuum collaborate effectively to reach their common goal.

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Bringing It Together

In working along the research continuum towards farmers' adoption of sustainable systems, three challenges present themselves. First, a range of technologies must be integrated at the farm level. This process is far more complex than promoting a single change in management in a farming system. Second, given the enormous size of the task literally every farmer's field in the world there must be an effective and efficient way to "scale up" from individual research sites. This issue is particularly important for CGIAR Centers working ecoregionally. Given these complexities, the third challenge is to develop and disseminate the information that all partners require to contribute effectively to sustainable farming systems.

Fortunately the tools of modern science show significant potential to meet these challenges. Computer simulation models of crop and soil processes, GIS, and user-friendly information systems are key elements of the research process for sustainable intensification of agriculture. Aside from contributing to the development of risk management strategies at both the farm and national levels, these tools are also the most effective means of extrapolating information in time and space ­ that is, in addressing the issue of how to "scale up." To carry out the GxExMxP paradigm as effectively as possible, CIMMYT has recruited people with the skills to use and further develop these tools.

One example of the further development of tools for sustainable agriculture is the Sustainable Farming Systems Database (SFSD) currently being produced at CIMMYT. This database should vastly improve the collection, storage, and distribution of research information that is relevant to efforts to improve the sustainability of wheat- and maize-based farming systems. The SFSD is a flexible information system that brings together results on farming systems research, scaled from the experiment level to the farm level and the regional level. Data types include experimental results, surveys, expert opinions, results of on-farm monitoring, census data, and scouting reports. Any data source can be georeferenced and linked to information on researchers, institutions, and associated bibliographic material. The SFSD permits flexible queries about locations; single crops or rotations; tillage and harvest practices; use of labor, machinery, and chemicals; and system performance. Data can be extracted for use in other applications such as spread sheets, statistical packages, crop simulation models, and GIS. Available on CD-ROM and through the Internet, the SFSD will facilitate a global interchange of research experience related to cropping systems and their impact on the environment.

Information technology is therefore crucial to sustainability, and CIMMYT is committed to making information available in the most accessible and efficient form for its partners. This technology has a vast and still underexploited potential to greatly increase research efficiency by linking information across disciplines and geographical locations.

Another example of the power of new information tools is our International Wheat Information System (IWIS), available in CD-ROM.³ Local naming conventions for wheats once precluded efficient communication among researchers, but by identifying germplasm unambiguously, IWIS removed the barriers to the association of different kinds of information on wheat. Marrying the management of performance data with the principle of unique identifiers has provided unanticipated querying power and enabled multidisciplinary data integration. Through the IWIS CD (which features family trees for more than 1.7 million genotypes and performance data from 77 countries), information from diverse sources is integrated, linked to sources of seed, and put to work in wheat improvement. Major new insights into adaptation are being gained through feedback between genetics conventional and molecular and environmental information. Displaying genetic information on the branches of family trees of individual wheats facilitates genetic inferences, helps plan strategic crosses, and reduces laboratory testing. For example, when the database shows that the direct parents of a cross do not differ for an important gene, the gene can be inferred in the progeny, thereby saving the cost of direct testing. Other major savings and benefits to date include quantifying the genetic diversity in farmers' fields, tracking seed stocks so they may be replaced after civil crises, eliminating repeated introductions of wheats to collaborators (and the associated quarantine costs), and global sharing of information on genes for bread making quality. Now that the IWIS CD has been distributed to 78 countries, CIMMYT is committed to providing write-access to IWIS for researchers in developing countries. This will result in a highly streamlined, multi-directional information flow and full participation of partners in NARSs.

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Achieving Impacts

We know that the sustainable intensification of agriculture in farmers' fields is not merely a desirable achievement but an essential one. With 200 people added each minute to our global population, and with all of us dependent on a shrinking agricultural land base, sustainable intensification is the only practical and appropriate choice for the foreseeable future.

The time for talking is over, and the time for concerted action is here. To act to truly address the GxExMxP paradigm we need strategic partnerships, and as partners, we must bring to the table all the available and appropriate technologies. Let us not argue about whether a given technology will work; instead, let us focus on how we as a team can make it work, and work well.

Biotechnology is a key tool that must be brought to bear on the traits that save lives apomixis, drought tolerance, and resistance to pests and diseases. In the debate over the applications of biotechnology we have been distracted for too long by flavorsome tomatoes, "designer" chocolates, and potatoes that do not turn brown when cut early for dinner. This is biotechnology for the well-off, who quite rightly can choose whether to take it or leave it! The resource-poor have no such luxury. They need drought-tolerant maize now.

As I have emphasized here, "business as usual" will not achieve sustainable intensification of agriculture in farmers' fields. We must plan and respond to change, for sustainability is a moving target. CIMMYT has changed to build on its strengths in G, through greater in-house emphasis on ExMxP, and with a view to building strong alliances with partners who have strategic strengths in these areas ­ be they NARSs, ARIs, NGOs, the private sector, or other Centers. Together we can prevail, and prevail we must.

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Acknowledgments

This paper could not have been prepared without significant input from several colleagues. The contribution of Larry Harrington, Director of CIMMYT's Natural Resources Group, was invaluable and provided many practical examples to support the concepts. Kelly Cassaday also made a major input and she and Miguel Mellado oversaw editing, design, and production. Internet version by María Delgadillo and Pedro Santamaría. Valuable contributions were also received from Paul Fox, Joost Lieshout, and Mauricio Bellon.

Notes

¹ This section draws heavily on Byerlee (1994).

² This research emphasizes the earlier point that action ­ and real progress ­ to achieve sustainable systems requires collaboration. CIMMYT has not made progress in developing stress tolerant maize by working alone; this work has been supported by the United Nations Development Programme (UNDP), Swiss Development Cooperation (SDC), the International Fund for Agricultural Development (IFAD), and the Swedish International Development Cooperation Agency (Sida), and the research has also been planned and conducted in conjunction with the Maize and Wheat Improvement Research Network (MWIRNET) (funded by the European Community) the Southern African Centre for Cooperation in Agricultural Research (SACCAR), and the International Institute of Tropical Agriculture (IITA).

³ The latest edition has been distributed to more than 1,000 partners around the world.