Introduction

Agro-environmental issues are not new to governments, environmental groups, citizens and producers. More recently, the environmental challenges facing agriculture have broadened to include acceptable levels of environmental quality and quantity as the agriculture sector has adopted new intensified production methods to meet the growing demand for agricultural products by society. Consequently, the farmer is now called upon to fulfill the conflicting roles of steward of the countryside and provider of food, while his or her activities come under increasing scrutiny.

Manipulation of Agro-ecosystems

Agroecosystems are characterized by driving forces that include market signals, government policy, production technology and farm practices. Variables or inputs include inflows of capital, information, energy, fertilizers, chemicals, and human infrastructure and knowledge. Natural driving variables or inputs include solar radiation, rain, wind and water. Most agroecosystems also experience losses or outflows from the system such as water, and emigration of inputs such as nutrients and pesticides. Agriculture is influenced by human manipulation of natural ecosystems. This influence includes genetic alterations, pest management and yield goals.

Domesticated Plants and Pest Resistance

Major disease epidemics, insect outbreaks and problem weed infestations are common occurrences in agro-ecosystems. These occurrences are rare in natural systems relative to cultivated systems because of inherent diversity in natural systems. In natural systems, few niches are available for any single species. In most agriculture systems, crops are grown as a single genetic type grown over vast areas.

Plant breeders, entomologists and pathologists have had tremendous success in developing resistance to limit epidemics and infestations, however, there appears to be no relief from ever adapting pest populations. Even when resistance is incorporated into new varieties it usually breaks down over time and new pest races are no longer susceptible to the simple resistance trait. By increasing the number of resistance genes that control a pest (multiple resistance), plant breeders have increased the durability of crop resistance to diseases. Biotechnology techniques are available to easily combine many specific resistance genes into one genotype. Breeding programs continue to successfully incorporate new sources of resistance into plants, but have certainly not found solutions that will work indefinitely. Pest mutation, diversity and adaptation make this process a constant battle.

Pest in Agro-Ecosystems

Crop yield losses from pests range from 0 to 100% in a particular area. However, in an average agricultural setting, crop yield losses due to pests probably ranges from 10 to 40%. Three decades ago returns for pesticides were much higher (up to $16 for every dollar spent). Nevertheless, even current levels of return are very impressive if dollars spent on pesticides are the only cost.

Pests also cause losses other than yield, such as lower crop quality, more human labour, reduced equipment and fuel efficiency and lower market acceptance for agricultural products. In addition, areas put into production to compensate for pest losses (marginal land, rain forests, drained wetland and marshes, etc.) enforce costs on ecosystems and the environment. It is important, however, to consider that these same sensitive areas are most often put into production simply to satisfy the profit motive. Pests limit the efficiency of management inputs such as nutrients supplied to crops and reductions in those efficiencies can also be responsible for environmental degradation.

Yield Goals

Maximum crop yield will vary depending on the genetic potential achievable in a healthy plant and the environment in which the plant is grown. Local knowledge of the environment is required to set realistic yield goals. It is neither biologically efficient nor sustainable to manage fields for yield goals significantly higher or significantly less than the attainable yield, given local environmental limitations.

A healthy crop not only yields more food, fibre and profit, it is also less likely to leave unused nitrates, which may leach through the soil profile and contribute to groundwater pollution. A healthy, high yielding crop also returns more OM to the soil than one with inadequate nutrients or pest management. A crop that yields well below what is attainable because of inadequate protection from pests and disease is also likely to use nutrients and water less efficiently, return a smaller profit and contribute fewer residues for erosion control and maintenance of soil OM. Perhaps maximum environmental “yield” will be considered in the future.

Fifty years of scientific progress and innovation in plant and animal breeding, irrigation, pest control, fertilizer technologies, labour-saving technologies, and food processing have enabled food production to keep pace with the demands of a growing human population. To meet the demands of increasing populations, food production must double over the next 30 years. Innovation and technological breakthroughs must continue at the same or a more rapid pace to meet this demand. The challenge is to manage for attainable and affordable yield in a global economy/system that is becoming more uncertain as climate change and societal demands for sustainability become more certain.

Sustainable Agriculture – Ecosystem Services

The apparent success of production in meeting the increasing demand for food and fibre in the last 50 years depended on manipulation of capital held in the form of soil OM, nutrients, water and fossil fuels – ecosystem services. Natural systems provide goods and services that create and regenerate soil fertility, moderate regional climate, remove and restore carbon dioxide, minimize flooding, degrade plant litter and animal wastes and purify water. An unintended outcome of the intensification of agriculture is global degradation of soil and water resources, air quality, and the loss of biodiversity. Thus, the earth’s agroecosystems have become increasingly stressed by economic/profit activities while at the same time there has been little scrutiny or pressure placed on governments and farmers to maintain acceptable levels of environmental quality and quantity.

Ecosystem services are generally not factored into the costs of economic output, yet economic output is not possible without nature’s system. The economy must be put in synchrony with the natural world that makes it possible. Detrimental environmental impacts of agricultural practices are costs that are typically unmeasured and often do not influence farmer or social choices about production methods. Some scientists are currently trying to quantify the benefits of ecosystem services and the impact of agriculture practice on them to identify options that would lead to a more sustainable agriculture. Questions have arisen as to the sustainability of our past success and the ability to meet the challenge of doubling production over the next 30-50 years.

Healthy soil is critical to short and long-term crop productivity, preserving ecosystem services and economic growth. Soil OM combines water, minerals, and soil microbes in a matrix that contributes to the health of agro-ecosystems. Topsoil is the reserve wherein soil OM exists and any damage to this reserve leads to environmental degradation. Some farm management practices (indiscriminant use of inorganic fertilizers and pesticides) contribute to these degradative processes, hastening symptoms and effects. Other management practices help to stabilize or improve soil quality (zero tillage, diverse cropping systems, nutrient management plans, etc.). The loss of OM represents a real loss in economic returns. Breakdown of soil structure, damaged roots and crop health reduce yield. Increased costs of replenishing nutrients are needed to maintain crop yields. Improving resource efficiencies will increase profitability and conserve natural resources. The real challenge is to develop more productive, soil building production methods. Essentially this means improving the efficiency with which nutrients, water and other inputs are utilized and returned to the production system.

Beyond IPM – An Integrated Approach Towards Sustainable Agriculture

Goals of enhanced food and reversing environmental degradation are not mutually exclusive. Degraded agro-ecosystems are less resilient to intensification and stresses caused by climatic changes. The international community has responded by establishing numerous agreements (Kyoto, 1997), international conventions, and research and development programs that endeavor to enhance the activity in sustainable agricultural development (e.g., World Bank, 1995). One consequence of these developments has been the growing support of more holistic agroecosystems as the new paradigm for sustainable production.

That is, an agriculture defined as an approach that systematically attempts to incorporate more biological processes and natural cycles into the farming system to reduce the use of off-farm inputs with the potential to harm the environment, farmers or consumers. This type of agriculture would improve the match between cropping patterns, production potential, and physical limitations of the land and climate and emphasize profitable, efficient production while conserving soil, water, energy, and biological resources. Combining knowledge of climate, soil, and agronomic principles can remedy short-term challenges and support long-term soil, root and systems health and enhance nature’s services.

Pesticides dominate the tools used in pest management systems partly because researchers and industry have studied pesticides most extensively, and partly because pesticides offer simple and cost-effective, albeit short-term, solutions to difficult problems. The extensive and continued use of pesticides has led to ever-increasing cases of resistance to pesticides and ecosystem degradation.

IPM research focuses on combining several pest management tools into diverse cropping systems. For example, weed management is enhanced when competitive cultivars are augmented with higher seeding rates or farmers introduce operational diversity that may leave pests that are adapted to conventional systems “unprepared” to compete and thrive. More IPM research should focus on why pests are present rather than on their management. IPM requires less man-made inputs and more knowledge. Figure 1 illustrates the extremes of technological inputs versus biological inputs and higher knowledge-based management. Urban pressure to reduce pesticide use, pesticide resistance, and high input costs may push growers to adopt IPM and alternative weed management systems to a greater degree than they, or many researchers, are currently comfortable with or prepared for. It is clear that more knowledge of sustainable systems are required.

Nevertheless, a program aimed at holistic health may still require the use of synthetic pesticides. Pesticides should be viewed as a supplement and not the first line of defense or a substitute for other practices. Pesticides provide some protection against damage from a pest favored by environmental, nutritional or soil stress on a crop. However, pesticides are not justified as a means of permitting the growing of susceptible varieties if a resistant variety is available or as a substitute for certified seed or other good agronomic practices.

Successful crop production, regardless of the methods used, is a careful piecing together of numerous components into a system. IPM cannot be successfully implemented, and crop health cannot be achieved, if pest management is the exclusive focus of crop producers. Simply replacing one component with another is seldom successful. Focusing on crop competitiveness and crop health will lead producers to rely on packages of tools which include such things as sanitation, low disturbance seeding systems, higher seeding rates, narrow crop rows, optimum fertilizer placement, and diverse crop rotations. Poor fertility can reduce crop health to the degree that all of the tools employed for pest management are negated. Similarly, good disease and insect management, in some situations, may be more important for weed management, because of their impact on crop health, than for their direct effects on crop yield. A healthy, competitive crop is the key to ICM in any cropping system.

Meeting the Challenge of Environmentally Sustainable Agro-ecosystems

Agriculture will influence soil, air, water, nutrients, microbes, arthropods, and numerous other organisms. Attempts to manage natural resources, given the complexity of our ecosystem must include considerations for the entire system. In the past, our best efforts to improve Nature have usually foundered on some factor we failed to consider. Technology cannot be treated as and end in itself. We need to be careful not to justify technology because it is feasible, but because it is both necessary and risks from its use are low.

Further impacts to the agroecosystem will develop as human activity increases, intensification of production continues and new technology is adopted. Farming systems that are ecologically and socio-economically sustainable will become more integrated. The need for the development of predictive tools and ecological and environmental indicators will be necessary to evaluate these systems. Research on impact, adaptation and mitigation research of PMS requires models to explore and minimize the impact of environmental change. Scientific challenges include improved agriculture ecosystems to increase yield, decrease reliance on pesticides and minimize inefficient use of all manmade and natural resources.

Selected Reading

Buhler D.D. (1999). Expanding the context of weed management, 289 pp. New York: The Haworth Press.

Carter M.R. (2001). Researching the agroecosystem/environmental interface. Agric. Ecosyst. Environ. 83:3-9.

Cooke R.J. and Veseth R.J. (1991). Wheat Health Management. APS Press, St. Paul, MN. 152 pp.

Edwards C.L., Lal R., Madden P., Miller R.H., and House G. (1990). Sustainable Agricultural Systems, 696 pp. Soil and Water Conservation Society, St. Lucie Press, Relray Beach, FL.

Gregory P.J. and Ingram J.S.I. (2000). Global Change and Food and Forest Production: Future Scientific Challenges. Agric. Ecosyst. Environ. 82:3-14.

Savory A. (1988). Holistic Resource Management, 564 pp. Washington, DC: Island Press.

Stern V.M., Smith R.F., van den Bosch R., and Hagen K. (1959). The integrated control concept. Hilgardia 29:81-101.

Stinner B.R. and House G.J. (1988). Role of ecology in lower-input, sustainable agriculture: an introduction. Amer. J. of Alternative Agriculture 2: 146-147.

Wallace J.S. (2000). Increasing agricultural water use efficiency to meet future food production. Agric. Ecosyst. Environ. 82:105-119.

FIGURE 1. The relationship between high technology input, low diversity systems and high biological input,
high diversity systems and long-term environmental and economic sustainability in plant management systems.