Agroecology – science for a sustainable agriculture


\"\"I\’m teaching Sustainable Agriculture again this fall at the University of Massachusetts and one of the questions that often arises is \”what sort of research should the university be doing to move us toward a more sustainable agriculture.\”  I\’ve been thinking about this for a long time – the answer is agricultural systems ecology (or agroecology for short).

\"\"Agroecology is the framework which will allow us to scientifically address multiple interrelated objectives of economic viability, social equity, and environmental integrity. An agroecosystem may be a field, a farm, or a larger region such as a river valley.  Implicit in agroecological research and education is the idea that knowledge of ecosystem relationships will allow farmers to manage inputs and processes in agricultural production systems and thereby optimize for productivity, sustainability, stability and social equity.

A systematic research method for agroecosystem analysis was described by Gordon Conway, of the Centre for Environmental Technology at the Imperial College of Science and Technology in London (Conway, G. 1985. Agroecosystem Analysis. Agr. Admin. Vol. 20:31-55).  Agroecosystem analysis is based on ecological principles that govern relationships among biotic (living) communities and the abiotic environment.  Biotic relationships may be described by principles of predator/prey interactions, competition for food sources and habitats, cooperation and commensalism etc.  Abiotic relationships are described by nutrient cycling, carbon cycles, energy cycles, etc. over space and time.

Conway suggests that four system properties may be used to understand the dynamics of an agro-ecosystem.  They are;

  • productivity,
  • stability,
  • sustainability, and
  • equitability.

Productivity is the quantity of product or output from an agroecosystem per unit of some specified input. For an agroecologist, output may include a marketable product such as bushels of corn, as well as negative products of a system like water runoff, pesticides leaking from the system, or soil lost. Of course, tons per hectare is a standard measure of productivity. But productivity can also be expressed in other units of output per unit of input. Inputs may be measured in tons of fertilizer, monetary value of pesticide, or kilocalories needed to deliver irrigation water.

Stability is consistency of production in spite of short term upsetting influences such as uneven rainfall, pest explosions, price variability, etc. Annual variations in productivity indicate a lack of stability.

Sustainability is the ability to maintain a desired level of production over time, in spite of long term destabilizing influences. Examples of these are; increasing soil salinity, off-site effects of soil erosion, declining market prices, or accumulation of biotoxins in the environment. Systems which rely on heavy inputs of non-renewable and rapidly diminishing resources are not considered to be sustainable. Sustainability is a measure of persistence or long-term resilience of a production system.

Equitability can be used as an indicator of agroecosystem performance which incorporates the social dimension. Social equity is a measure of the degree in which resources and products of a production system are equally distributed throughout the human population. This implies that equality of product availability (output) and equality of resource availability (inputs) are the preferred norm.

A research and/or educational institution that employs agroecosystem analysis will probably conduct more studies on complex relationships among the various components of a agroecosystem that go beyond simple cause and effect.  There will be more research on inputs and outputs that are measured in currencies other than monetary units, such as carbon, nitrogen, and calories.  This will provide the basis for better nutrient management recommendations. There will be more studies on relationships among pest populations, predator populations, host populations (both agricultural crop and non-crop species), and environmental influences on these. This will provide the basis for better pest management recommendations. There will be more studies on interspecific relationships among crop plants and the effect of these on pest populations. This will provide the basis for innovative multiple cropping systems.

\"\"Ecological principles will provide an appropriate framework in which to better understand and manage the impact of agricultural systems on the food supply, the environment and people. I believe that ecological approaches to agriculture can be the common ground upon which we address the needs of society, while employing the tools of scholarly research and teaching, for which public institutions are best equipped.


This paper was presented by John Gerber,  as part of a U.S.A.I.D. sponsored workshop on sustainable agriculture in Lusaka, Zambia, September 18-21, 1990.


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