The term "sustainable agriculture" is based on the word sustain. Thus, before discussing the term"sustainable agriculture" it is helpful to examine a definition of the word sustain. Sustain includes the idea of "keeping up", "supporting" "enduring" and prolonging". Thus, sustainable agriculture implies an agricultural system that will be prolonged, that is, it will continue to operate over a long period of time.

There are many ways to describe how agriculture can be sustainable. The following list summarizes key components of sustainable agricultural systems that have been suggested by various authors.

  • a careful stewardship of the earth
  • the maintenance of the earth's biological systems
  • the maintenance of nutrient cycles
  • an ability to meet the need for food indefinitely
  • a system that produces food at a socially acceptable environmental cost
  • an acceptable balance of environmental and economic concerns
  • an incorporation of biological processes such as: nitrogen fixation and beneficial insects into food production
  • minimal use of off-farm inputs
  • use of crop rotations to control weeds, diseases and insect pests
  • the use of integrated pest management
  • the use of no-till or minimum-tillage cropping systems

The American Society of Agronomy has developed the following definition of sustainable agriculture:

" A sustainable agriculture is one that, over the long term, enhances the environmental quality and the resource base on which agriculture depends; provides for basic human food and fiber needs; is economically viable; and enhances the quality of life for farmers and society as a whole." (Francis, C.A., and G. Youngberg. 1990. Sustainable Agriculture--an overview. In C. A. Francis, C.B. Flora, and L. D. King (eds.), Sustainable Agriculture in Temperate Zones. John Wiley and Sons, New York, pp.1-23.)

A properly managed system where forages are fed to livestock, like the type described in the previous paragraph, has a number of features that develop sustainability. As indicated in the previous section, sustainable agriculture implies limited outside inputs and minimum tillage. Forage-livestock systems often incorporate both of these features. Unlike agricultural systems in which crops are grown and harvested within a single growing season, maintaining forages in pastures involves much less disturbance of topsoil. Because this generally results in lower rates of soil erosion, the sustainability of soil as a resource can be greatly improved. In addition, the maintenance of forages in pastures over long periods of time enhances the build up of soil organic matter and humus, which in turn help sustain soil fertility. Legumes, crops that are able to extract nitrogen from the air and add it to the soil, are often included as forages in pastures. The presence of legumes provides an input of nitrogen into the system that can make up for nitrogen removed from the system within animal products like milk and meat. Thus, including legumes in the system helps make the system more of a sustainable system.

The recycling of nutrients is a vital part of sustainable agriculture. When animals eat forages, they consume nutrients and utilize some of the nutrients to grow, produce milk and maintain body functions. But significant quantities of nutrients are deposited onto the ground in waste products. The waste products are recycled immediately into the soil in a form that can be readily used by forage plants. This natural recycling of nutrients lessens the need for off-farm fertilizer nutrients, which is an important component of sustainable agriculture. It has been predicted that there will be an increase of five billion in world population over the next 40 years so learning to recycle the existing nutrients is crucial (Council for Agricultural Science and Technology, 1994).