There are two measures of sustainability to be considered, the economic and the physical. Richard Gray 1 among others has devoted considerable efforts to development of economic measures, while the work of Zentner 2 provides an insight into determination of the physical as related to the soil resource used in agriculture. An economic measurement of sustainability is difficult, as there are several viewpoints to consider. Gray stated that two general views prevail concerning sustainability in agriculture, one by consumers and one by producers. Consumers view sustainability in terms of its capacity to provide an abundance of quality food.
Producers view sustainability as an income generating activity with economic and social value.
The concern they have is with maintaining a net return from the sale of agricultural products. In economic terms, consumers assess sustainability in terms of maintaining a level of consumer surplus in the consumption of food over time. This dichotomy of interest provides a basis of conflict and attracts attention to the difficulty experienced when trying to measure sustainability. From the consumer's standpoint, security of the food supply is uppermost particularly among those who have previously experienced shortages or indeed famine. Measurement of the value of food security becomes almost impossible.