Estimating resource use efficiencies in organic agriculture: a review of budgeting approaches used

The basis of organic farming is that it is environmentally, socially and economically sustainable, and it aims, wherever possible, to use renewable resources in the production system and avoid waste. Thus this review considers the use of nutrient, energy and water within the farming systems, and indices that are used to evaluate the use of these resources and hence their impact on the environment. It is crucial that the delineation of system boundaries in both time and space, including both the vertical and horizontal dimensions, is defined to assess the resources used within the system. There is increasing interest in the emergy concept, which permits different forms of energy to be compared on the same basis. Across all farming systems, there is no direct link between nutrient surplus and nutrient loss. It is important to recognise that the choice of tool used to assess the environmental consequences of the farming system, as well as whether the results are expressed on a product or an area basis, may have implications for how emissions are attributed to different parts of the production system. In order for indicators to be useful, they must be influenced by the farmer's management practices.