The meaning of sustainability is a very debatable topic for it involves time frames, differing scales in space and levels of permanence [eds Edwards et al. 1990; Roberts, 1995; Campbell, 1994; Reeve, 1990], which are open to interpretation for individuals' concepts of sustainability are influenced by their particular image of the world or Weltanschauung and these interpretations are normally taken for granted [Checkland, 1988]. The interpretation of the meaning of this dynamic word is also dependent on which definition is used, for example sustainability relates to: maintenance, support and prolongation [Wilkes, Krebs, 1987; Barnhart, Barnhart, 1977; Tulloch, 1991]. In environmental jargon sustainability relates to an activity or the use of a resource;

"over an indefinite period without damage to the environment; [of a resource]
that can be used at a given time without permanent depletion, renewable." [Tulloch, 1991, p.279].

Within an agricultural context a sustained yield is;

"the continuing yield of a biological resource, such as a forestry or fishery crop,
by special, controlled harvesting, usually aimed at a steady optimum yield."
[Barnhart et al. 1977, p.2113].

The previous definitions have taken the meaning of sustainability within an ecological framework that can be associated with ecologically sustainable agriculture [Zarsky, 1990], but there is another important framework, which interprets the meaning of sustainability from an economic perspective. Economic sustainability [Zarsky, 1990] is often associated with shorter time frames than an ecological approach and makes the general assumption in an agri-business that as long as profit is forthcoming on a continual basis, it is sustainable.

The term 'sustainable' has entered into popular use and is applied to many situations. For example, the economic sustainability of an industry or the sustainability of an individual's income, is often the farmer's first priority [Haines, 1982]. Economic stability is also subject to economic factors beyond the farmer's control as commodity prices can be seasonal and in a constant state of flux reflecting changes in supply and demand. Crews, Charles, Mohler and Power [1991] argues that the economic viability of sustainable agricultural systems is constrained by the social structure of agriculture and that sustainability itself is constrained solely by the ecological conditions of agriculture. Hence, there is a need for ecological sustainability which Lowrance, Hendrix and Odum [1986] describe as 'the ability of the catchment or land system to maintain the services that ecosystems provide [e.g. clean air and water]" [Reeve, 1990, p.6]. Lowrance [1990] has further defined this term as "the ability of life support systems to maintain the quality of the environment" [Lowrance, 1990, p.51]. Murphy [1994] recognised that this term is increasingly being used and reflects a growing awareness of natural environmental and biological factors that are an essential foundation for agriculture.

Sustainability is an important issue, although it's interpretation can be narrowed or used as an umbrella term. For example, Conway [1985] as reported by Campbell [1994] has established a narrower definition of sustainability, which is complemented by 'productivity', equitability and stability. Sustainability as an umbrella term also has its limitations as issues involving sustainability have become blurred and confused [Crews et al. 1991; Campbell, 1994], particularly in the relationships of ecological, social and economic parameters. In an attempt to clarify the integration of these parameters, Campbell [1994] has developed a hierarchy of dominant constraints and goals that are placed within a framework of different scales in time and space. Campbell's work forms the core of an enlarged hierarchy of sustainability. Finally it would appear that the meaning of sustainability is in the eye of the beholder [Campbell, 1994] and although a precise definition of sustainability may be elusive [Kenney, 1991] the author supports Kenney's [1989] opinion, which simply expresses that sustainability is "forever," however this interpretation is also the subject of conjecture [Carter, 1989; Lockeratz, 1988; Ruttan, 1988].