Modelling sustainability at the farming system level : an approach based on insights from thermodynamics

![CDATA[Sustainability has an environmental bottom line and is underpinned by the laws of thermodynamics. Drawing on the insights from the laws of thermodynamics, the modelling approach at the farming system level was based on two high level criteria for sustainability: efficient use of energy and non-degradation of the environment from energy and material use. Indicators, such as the energy ratio, carbon ratio, soil carbon level, nutrient balances and leaching of N, which are consistent with the two sustainability criteria were identified for an organic orchard system. Two computer modelling tools (Stella® and Overseer®) were used to estimate sustainability indicators using primary and published data. Sustainability modelling of the organic orchard systems in New Zealand suggests that the approach is useful for evaluating energy efficiency and key environmental impacts that occur in soil, water and atmosphere. The findings also suggest that the model is capable of guiding management decisions to move towards more sustainable practices. Further research to improve and validate the proposed approach is essential before it can be used for decision-making at the orchard level and for policy-making at the national level.]]