Emergy unsustainability index for agricultural systems assessment: A proposal based on the laws of thermodynamics

Abstract

The anthropic effects of agriculture call for more sustainable systems. Agricultural sustainability conventionally communicates an idea of perennity. However, the sustainability of living open systems, like agricultural systems, can be regarded as a mere utopian idea when the effects of the laws of thermodynamics are taken into account. Under such physical laws, what really exists is the fact that any system alone has the property of unsustainability. The rate of entropy production can denote the potential level of the unsustainability of a system. The higher the rate of entropy production in an agricultural system, the higher its potential for unsustainability. Directly measuring entropy in living open systems is unfeasible. Even so, such systems are subject to the laws of thermodynamics. Indirect measurements of entropy in living open systems can be assessed by approximation through an analysis of the energy flows of the system. We used emergy analysis to account for the energy flows and compare the unsustainability among agricultural systems. However, the indicators proposed by emergy analysts have been more aligned with the perspective of sustainability. To change this perspective, we propose an emergy unsustainability index applied in this paper specifically to agricultural systems (EUIAS). EUIAS is not a simple inversion of the ESI obtained by the ratio between the Emergy Yield Ratio (EYR) and the Environmental Loading Ratio (ELR). The use of renewable exergy stored from one production cycle to another is one of the peculiarities of long-term agricultural systems. Therefore, quantifying the renewable and non-renewable fractions of resources used is fundamental to the EUIAS. A higher EUIAS means that an agricultural system is more dependent on non-renewable economic resources than renewable resources, and, in general, environmental impacts are higher due to the use of non-renewable resources.