0 Rees, RM. Topp, CFE Watson, CA 2006 Aspects of Applied Biology 80 203-206 <p>Sustainable farming systems are required to achieve long term economic, social and environmental continuity. Sustainable resource use (nutrients and energy) is a critical component of such systems. It has been argued that organic farming systems achieve a high level of sustainability, and it is likely that modifications to the management would alter their environmental impact. The potential for a range of organically managed farming systems to contribute long-term sustainable resource use has been studied using a modelling approach. The DNDC (DenitrificationDecomposition) model has been used to compare different rotational designs (ranging from continuous grass to continuous arable) and site conditions on nutrient flows. Key carbon and nitrogen fluxes are described and indices that can be used to help define relative resource use efficiency (nitrogen input/output ratios and net global warming potential) are presented. The approach used in this study provides a valuable means by which the design of farming systems can be improved to deliver environmental benefits that will be required in future years.</p>