To further expand on the meaning of sustainability, the assumptions made about sustainable development need to be confirmed. The issues that are to be discussed are of importance as they directly relate to the underlying philosophies and concepts of sustainable agriculture, which are an offshoot of the larger debate on sustainable development [eds Edwards et al. 1990]. The debate over sustainable development has influenced the direction of sustainable agriculture [eds Edwards et al. 1990] and opens up the debate in a manner which is very different from the traditional approach to economics and has raised issues that involve ethics, biodiversity, the global dimension and intergenerational equity. The four main topics to be discussed in regard to sustainable development [Bierbaum, 1991], which are also applicable to sustainable agriculture, are:

a]. Economic progress to improve the well-being of the community.
b]. The provision of equity between generations.
c]. Protection of biodiversity and the maintenance of ecological processes and systems.
d]. The recognition of the global dimension.

Economic progress to improve the well-being of the community

The path of economic progress cannot be simplified into black and white issues as there are economic, ecological and many other innumerable factors to consider [Crews et al. 1991]. People regard economics and ecology as very different subjects and they are sometimes presented as opposite opinions. Part of this division can also be attributed to economists studying their traditional subjects and ecologists doing likewise, each finding jobs and networks in their own fields. The parties rarely meet and barriers can be formed which are slow to break down and yet both are vital to sustainable agriculture [Johnson, Warding, Gorrie, 1990].

The debate over economics versus environment is presented in its simplest form below. The ecological viewpoint, is that economic progress is not sustainable as the global community relies on a planet with finite resources where there are natural limits to economic development [Bierbaum, 1991]. For example, if land use is unsustainable, so is its economic productivity. The pure economic paradigm makes the assumption that the environment is a "free good" which, by choice, can be exploited or nurtured. Bierbaum [1991], gives an example of an individual benefiting from driving a car, but the cost of the air pollution is borne by society as a whole. In a similar fashion farmers benefit from the use of phosphate and nitrogen fertilisers, but again society directly or indirectly has to bear the cost of algal blooms and ground water contamination. Both Bierbaum, [1991] and Beatley [1994] recognise that the environment needs to be treated as an asset and polluters must be made accountable and pay for their actions. In contrast Campbell [1994] judged that it is unrealistic for farmers to pay for restoration of the landscape that they own, for they often simply cannot afford it. An even softer and politically safer stance is taken by the Commonwealth of Australia [1991A] which states that there should be no admonition of past practices as they were often undertaken in good faith and sanctioned by governments.

The provision of equity between generations

As previously discussed consideration needs to be given to future generations. The concepts of sustainability and obligations to those generations are closely linked [Beatley, 1994]. This linkage includes the issues of the provision of resources between generations and the options of future generations needing to be kept open [Bierbaum, 1991].

Intergenerational equity is the passing on from one generation to the next a stock of both human and natural capital which is no less than that inherited by our generation. Currently this is clearly not occurring as non-renewable and natural resources are being exploited to serve the current generation.

An important part of the debate on equity between generations involves resources and before further discussing this issue, it is necessary to clarify the difference between renewable and non-renewable resources. This is a complex subject to define, but in simple terms non-renewable resources, typified by fossil fuels, are depleted by use and renewable resources are not. The latter can be divided into two sub-groups, being a flow resource e.g. solar energy, or secondly through biological growth. Traditional agriculture has relied on both renewable sub-groups, whereas modern agriculture has in addition a high reliance on non-renewable resources [Lecomber, 1979]. In contrast modern agriculture is increasingly using non-renewable fossil fuels and synthetic chemicals which is a non-sustainable long term practice [Odum, 1971].

Although there is a great emphasis on renewable resources being sustainable, it should also be noted that even renewable resources can become non-renewable. In a practical sense it could be argued that habitats and species are not renewable for they cannot be replaced. It is possible to deplete a renewable resource by using it faster than the renewal mechanism [Hartwick, Olewiler, 1986]. Historically, Flannery [1994] reports the well documented extinction of New Zealand's moas by the Maoris due to the over hunting of this food resource. On-going current examples of exploitation have occurred when underground water has been depleted by extensive agricultural irrigation, fish populations harvested to extinction and forests cut down resulting in soil erosion and the non- regeneration of trees. The cost of materials in particular has risen as low cost easily accessible natural materials such as alluvial gold, surface water, forests of high grade timber have been exhausted. Depletion of natural resources can occur not just in quantity but also in quality. Old forests that are logged and reseeded result in younger trees which do not have the same qualities as the original timber. There is a need for sustainable yields to occur so that the next generation can use resources such as those supplied by the oceans, forests and agricultural land [Commonwealth et al. 1991A].

In regard to the sustainability of resources, time appears to be a crucial element for while most natural resources are renewable the time needed for growth is the crucial component. For example, bacteria can breed in hours, whereas oil deposits take billions of years to produce [Hartwick, Olewiler, 1986]. Meadows, Meadows and Randers [1992] argue that fossil fuels are non-renewable on any time scale of interest to humanity and modern agricultural systems are irrevocable consumers of non-renewable resources, which are used through direct energy; i.e. in tractor fuel or indirectly in the form of synthetic fertilisers. With regard to the heavy use of fossil fuels it has been suggested by Green [1978], who adopts an over-dramatic stance, that our food is an accumulator of fossil fuel energy and developed countries are therefore "eating" oil, but the hoax is that industrialised civilisations no longer eat plants grown from mainly solar energy, but that we now eat plants that have an energy source that has indirectly derived from oil, a non-renewable resource [Odum, 1971]. It would appear that we are truly living in the age of hydrocarbon agriculture and 'hydrocarbon man' [Yergin, 1991].

The use of fossil fuels and the development of agrochemicals have allowed substantial increases in food production, yet there is a down side to this phenomenon for according to Meadows, Meadows and Randers [1992] human-synthesised chemicals are the most intractable hazardous wastes and are a definite threat to the health of future generations. This is due to the fact that they are often slow to break down and this increases the likelihood of their accumulation to dangerous levels [Meadows et al. 1992].

The current Australian community's standard of living and high consumption rates, are being paid for by depleting soil quality at the expense of future income and to the detriment of future generations [Commonwealth et al. 1991A]. In short, past agricultural production levels will not be sustainable, if the soil as a resource base is being over-worked and is declining [Lecomber, 1979].

This highlights an important issue in relation to the future of modern agriculture. Is soil, or more specifically top soil, a non-renewable resource? This is a commonly held assumption. If this were the case and this resource is non- sustainable, it can only be conserved for future generations. However, it is very apparent from Podolinsky's [1989] and Balfour's [1975] works that top soil is a renewable resource as it can be rapidly developed from the perpetual biological or living process, which can be sustained.