Defining the Need
As concerns about environmental protection, natural resource stewardship, and the world's ability to feed ever-growing populations continue to mount, the sustainability of agriculture and natural resources is emerging as a central theme among the public and policymakers alike. The importance given to it reflects the recognition that the quality of human life and the quality of the environment are inextricably linked. The issues involved transcend science. They encompass ideologies and values, ethics and aesthetics—the arena, in short, of public opinion and public policy. The issues also transcend national boundaries and involve critical considerations of intergenerational responsibility and equity.
The deepening awareness of the interdependence of agriculture, the environment, and socioeconomic conditions has called into question the sustainability of current agricultural production systems. In industrial countries, the environmental effects of intensified production have led many to search for ways to maintain and enhance productivity through better management of the entire agricultural system, including changes in socioeconomic incentives and policies.
The recent National Research Council (1989a) report Alternative Agriculture describes the human and environmental costs of high-input production methods in the United States. Based on a growing body of research and experience, the report examines the environmental problems that today's widely accepted agricultural practices can cause or fail to prevent. These include soil erosion and degradation, nonpoint source water pollution, groundwater contamination, salinization, aquifer depletion, loss of biological diversity, resistance to pesticides, and human health risks associated with pesticide application and residues.
The report calls attention to the economic and environmental effects of reduced reliance on chemical pesticides and fertilizers, and in a series of case studies describes the experiences of farmers who have adopted alternative practices, including crop rotation, integrated pest management, and increased use of on-farm nutrient sources. These innovative farmers have taken the lead in devising and implementing new management approaches on their farms, and the case studies document the results—the successes as well as the failures—from their fields, pastures, and orchards. The report argues that research needs to be directed toward alternative practices and improvements in technology and management know-how. It also calls for research on the social, economic, institutional, and policy factors that influence the choices farmers make. Such research can contribute to the formulation of incentive programs that encourage the development and adoption of beneficial alternatives.
Many of the same forces, trends, and interdependencies described in Alternative Agriculture are important in other areas and agroecosystems around the world. Additional factors, especially continued rapid population growth and crushing poverty, increase the pressure on the land and accelerate the processes of environmental deterioration. They are particularly acute in developing countries, where people are unable to buy food, governments are unable to purchase food on world markets, and distribution problems hinder availability even when local supplies are adequate. As some areas exhaust their supplies of arable land, inappropriate land use practices are causing massive soil erosion, critical losses of biological diversity, and general degradation of the natural resource base. In the tropics, where these forces are especially potent, the burning of rain forests to clear land for agriculture adds to the threat of global warming. Global agriculture and resource management thus face alarming problems as the twenty-first century nears.
AGRICULTURE, ENVIRONMENT, AND DEVELOPMENT
The human population is expected to increase by 1 billion people—the equivalent of an additional China—each decade well into the next century. Most of this population growth will occur in the developing nations, placing further stress on their arable land bases. In many countries, the limited availability of arable land, combined with urban congestion, has led to spontaneous and organized migrations and the clearing of new land for agriculture. Land clearing has contributed directly to the degradation of soil, water, and other natural resources in both humid tropical and semiarid countries.
In the humid tropics, conversion of the rain forest for agriculture, timber, and large-scale ranching is accompanied by the loss of topsoil and the depletion of nutrients, especially nitrogen, through leaching of exposed soil
or through volatilization by the burning of land for clearing (Lal, 1986; Pimentel et al., 1987). The loss of soil in the uplands results in degradation of inland and coastal waters and disruption of hydrogeological cycles.
The forests of the humid tropics are also the world's richest repositories of biological diversity, and deforestation threatens to drive many forest species, many not yet even identified by science, to extinction. Numerous reports (McNeely, 1988; Myers, 1980; National Science Board, 1990; Office of Technology Assessment, 1987; Wilson, 1988) document the value of biodiversity and describe the extensive and varied consequences for agriculture of reduced diversity. These consequences include losses of plant and animal species with the potential for domestication; genetic strains resistant to drought, pests, and disease; beneficial pollinators and symbionts; and pest antagonists, parasites, and predators. Destruction of the rain forests also contributes, through increased rates of biomass decomposition, burning, and oxidation of soil organic matter, to the buildup of atmospheric carbon dioxide and other greenhouse gases (Crutzen and Andrae, 1991; Houghton, 1990; Myers, 1989; U.S. Environmental Protection Agency, 1990).
In arid and semiarid areas, demands for wood, fuel, fodder, and shelter increase with the growth of populations of people and livestock. The environmental results are analogous to those affecting the tropical rain forests (National Research Council, 1984). In the Sahel, overgrazing by cattle and sheep, which in many areas have replaced browsing camels and goats, has resulted in the conversion of grasslands from deep-rooted perennial grasses and shrubs to annual grasses less resistant to drought stress. Deep-rooted leguminous trees and shrubs have also been increasingly harvested and burnt for fuel, and their role in water and nutrient cycling has diminished. Other species that depend on them for shade and nutrients cannot survive. The simplified soil and root structure is less able to absorb the moisture of seasonal storms, and the subsequent rapid runoff accelerates soil erosion, further inhibiting recovery.
Soil compaction and crusting, loss of soil organic matter, reduced soil-organism activity, and nutrient deficiency and imbalance reinforce one another in a cycle of resource deterioration (Lal, 1988). The interrelated effects of these conditions can be subtle. Soil erosion, for example, removes niches in which seeds germinate. Reduced numbers of trees and shrubs mean not only fewer seeds, but fewer birds and insects to spread seeds and pollen. Moreover, many trees must have their seeds pass through goats or camels before they can germinate. By such circuitous routes can the erosion of soil by wind and water, and the attendant loss of biological diversity, lead to land degradation and desertification throughout the world's arid regions.
In hill lands, the pressure of increasing population and the demand for land and fuel also lead to resource degradation, more marked because sloping land accentuates runoff and erosion (Jodha, 1990). Extensive deforesta-
tion can also affect entire watersheds. Reduced moisture retention in their upper basins can cause changes in the annual flood regimes of mighty rivers, such as the Nile, including severe flooding, and greatly reduced flow when water is most needed.
In input-intensive systems, such as the irrigated rice and wheat systems of Southeast Asia, high-yielding varieties produce two or more crops a year, with generous applications of fertilizers and pesticides. Recent reports (Byerlee, 1990; Ruttan, 1989) have described problems associated with maintaining current production levels, including the mining of trace nutrients, declining incremental response to increased fertilizer use, pest resistance, and reduced returns from additional research investment. In many input-intensive systems, water quality and availability are critical issues. In inadequately drained areas, irrigation is leading to salinization and consequent loss of productivity; in other areas, aquifers are being depleted. Contamination of groundwater is not yet as important a factor in developing countries as it is in some industrialized countries, but fertilizer and pesticide contamination of irrigation and other surface waters is important where these waters are also sources of drinking water or used for fish production.
The interrelated issues of population growth, intensified land use, environmental decline, and agricultural productivity at local and regional levels raise concerns about food security and quality, public health, and other long-term development problems. The issues are pertinent in all regions, but they are of special concern in the developing nations of the tropics, where the economic constraints and the development needs of rapidly growing human populations are most pressing. There, as elsewhere, environmental quality and development can no longer be separately considered. A quality environment and a healthy, stable resource base are essential for economic development, especially agricultural development. Conversely, ensuring a quality environment and resource base depends on changes in development policy and agricultural practices.
CHARACTERISTICS OF SUSTAINABLE AGRICULTURE AND NATURAL RESOURCE MANAGEMENT SYSTEMS
The concept of sustainable agriculture is a relatively recent response to interrelated environmental and economic concerns. Early discussions stressed the importance of maintaining the renewal capacity of agricultural ecosystems and claimed that many conventional agricultural practices were detrimental to that capacity. From further discussion has emerged an approach to agriculture that incorporates the principles of ecology by emphasizing interactions among and within all the components of agroecosystems.
As more individuals and organizations have begun to recognize the need for adjustments to conventional agriculture to make it environmentally, so-
cially, and economically viable, sustainable agriculture has come to connote approaches to agriculture that can provide for the needs of current and future generations while conserving natural resources. Indeed, a major development in the past decade has been the emerging recognition on the part of agricultural production and environmental management groups that they share common, rather than competing, goals. In this context, sustainable agriculture is often used to refer to agriculture and all its interactions with society and the greater environment; as such, sustainable agriculture can be considered a vital component of current discussions of sustainable development.
The definition of agricultural sustainability, it is frequently noted, varies by individual, discipline, profession, and area of concern. The literature offers hundreds of definitions of sustainable agriculture. Virtually all definitions, however, incorporate the following characteristics: long-term maintenance of natural resources and agricultural productivity, minimal environmental impacts, adequate economic returns to farmers, optimal production with minimized chemical inputs, satisfaction of human needs for food and income, and provision for the social needs of farm families and communities. All definitions, in other words, explicitly promote environmental, economic, and social goals in their efforts to clarify and interpret the meaning of sustainability. In addition, all definitions implicitly suggest the need to ensure flexibility within the agroecosystem in order to respond effectively to stresses.
The characteristics of sustainable agriculture provide a framework and suggest an agenda for the perpetual dynamic evolution of agriculture to meet the needs of changing societies and environments. Sustainable agricultural systems must maintain and enhance biological and economic productivity. The former is required to feed individual farm families and the nonfarm population. The latter is required to provide income for farmers and low-cost food for consumers. Ruttan (1988) has pointed out that, for both the developed and developing world, “any definition of sustainability must recognize the need for enhancement of productivity to meet the increased demands created by growing populations and rising incomes.” Others emphasize that enhanced productivity cannot be gained at the expense of the resource base, but in fact depends on constant conservation efforts. “High rates of soil loss are causing declines in soil productivity worldwide, and most nations do not have sound land use policies to protect their soil and water resources. The limited availability of fossil energy resources and their cost, which is expected to increase, make it unlikely that fertilizers and other inputs can offset severe land and water degradation problems, especially in impoverished nations” (Pimentel et al., 1987). Especially as the availability of new arable lands decreases, sustainability will require continual enhancement and improved management of soil and water resources and the protection of biodiversity in the system.
Sustainable agricultural systems should be both stable and resilient. Stability reduces risk and leads to continuity in income and food supply by fulfilling the short-term needs of farmers without incurring long-term environmental costs. Resilience permits adaptation to changes in the physical, biological, and socioeconomic environments. Sustainable agricultural systems should be environmentally acceptable; they should avoid erosion, pollution, and contamination, minimize adverse impacts on adjacent and downstream environments, and reduce the threats to biodiversity. Sustainable agricultural systems should also be economically viable in both the short and long term. Finally, they should be socially compatible with local people and political economies.
THE RESEARCH CHALLENGE: ADOPTING A SYSTEMS-BASED APPROACH
Fundamentally, achieving sustainable agriculture under the mounting pressure of human population growth will demand that the world's agricultural productive capacity be enhanced while its resource base is conserved. If the well-being of the world's less advantaged people is to improve in any lasting sense, long-range concerns about food security and the health of natural resources must be addressed in planning future economic and social development. Research will be essential to this task. More specifically, researchers must devote greater attention to developing integrated cropping, livestock, and other production systems—and the specific farming practices within these systems—that enhance (or, at minimum, do not degrade) the structure and functioning of the broader agroecosystem.
A primary objective of research on sustainable agriculture and natural resource management is the integration of information in its application to the problems of agricultural development (Edwards, 1989; Edwards et al., 1990; Grove et al., 1990). This process requires an approach to interdisciplinary research that includes the following: (a) identification of the components and interactions that determine the structure and functioning of the agroecosystem as a whole; (b) formulation of hypotheses that focus on those components and interactions within the entire agroecosystem; (c) examination, testing, and measurement of the hypotheses; and (d) interpretation of results as they pertain to the various components of the agroecosystem and to the system as a whole. A lack of understanding of the interrelatedness of system components has undermined agricultural sustainability in the past, and failure to consider any one of them fully will inevitably undermine it in the future. A systems approach to research is necessary if these shortcomings are to be overcome.
In the United States, the lack of systems research has been identified as a key obstacle to the adoption of alternative farming practices and as a neces-
sary step in the development of a more sustainable agriculture (National Research Council, 1989a, 1989b). In the even broader realm of international sustainable agriculture and natural resource management, the integrated research design, interdisciplinary participation, and systemwide perspective that the systems approach entails are necessary if the complex nature of sustainability is to be comprehended, the scientific basis of sustainability understood, and the threats to sustainability identified and addressed (Edwards, 1987).
Although the value of systems approaches has been increasingly recognized over the past decade, few crop and livestock production systems have been studied in detail. Agroecosystems are extremely diverse and variable, and thus the identification phase of research—the description of major components of the particular agroecosystem and the regional factors that act as constraints—is crucial.
A simple conceptual framework for the conduct of integrated agricultural systems research includes the following elements:
description of the target agroecosystem, including its goals, boundaries and components, functions, interactions among its components, and interactions across its boundaries;
detailed analysis of the agroecosystem to determine constraints on, and factors that can contribute to, the attainment of social, economic, and environmental goals;
identification of interventions and actions to overcome the constraints;
on-farm experimentation with interventions; and
evaluation of the effectiveness of newly designed systems, and redesign as necessary.
Techniques for describing agroecosystems have been reported in the literature (for example, Clay, 1988; Conway, 1985). A description of the agroecosystem components and boundaries is essential in providing a focus for study, but it should not limit understanding of interactions with adjacent ecosystems, or with local, regional, national, and international political economies. The description of the target agroecosystem must be based on discussions with farmers and other local sources of information and the recommendations of scientists from the range of relevant disciplines. Description of the components of an agroecosystem is the traditional occupation of many agricultural scientists, but description and analysis of interactions among its components require farmer participation as well as an interdisciplinary perspective and a whole-systems approach. Because proposed interventions are aimed at assisting farmers in attaining their goals, understanding these goals is especially important.
Although the descriptive phase of sustainable agricultural systems research is largely qualitative, the analytic stage takes maximal advantage of
quantitative information. The proposed descriptions may lead to hypotheses that require experimental study for resolution and quantification. For example, if nitrogen is suspected to be a limiting factor, then nutrient-response studies may be required. If losses to pests are hypothesized as an important factor, they can be quantified experimentally, and integrated management measures can be recommended for the pests identified. The result of the analytic phase is a more precise understanding of the factors that affect the attainment of the farmer's goals.
The design phase involves forming hypotheses about appropriate interventions that can contribute to the realization of the farmers' goals. It is a deductive process based on the description and analysis of the system. The final design represents the best collective judgments of the researchers and the participating farmers.
The evaluation phase assesses the interventions empirically and leads to further modifications. Effects must be measured in terms of the goals of the system, and trade-offs among goals must be determined for any proposed intervention. Interdisciplinary involvement and participation are essential in a successful evaluation phase.
As descriptive and analytic processes are employed in the study of agroecosystems in different regions and agroecological zones, the commonalities among them need to be emphasized and examined to elucidate their role in the functioning of the systems. Biological diversity, for example, is important to topsoil retention, nutrient cycling, and pest management in all agroecosystems. As these commonalities become better understood, they are likely to lead to global principles for the design of sustainable agricultural systems. The influence and importance of the commonalities may vary among agroecosystems, but research on them should be a high priority in all agroecosystems. Interdisciplinarity and integration will be fundamental to this effort.