Growing populations and a constrained fossil-manufactured energy supply present a major challenge for society and there is a real need to develop forms of agriculture that are less dependent on finite energy sources. It has been suggested that organic agriculture can provide amore energy efficient approach due to its focus on sustainable production methods.This review has investigated the extent to which this is true for a range of farming systems. Data from about 50 studies were reviewed with results suggesting that organic farming performs better than conventional for nearly all crop types when energy use is expressed on a unit of area basis. Results are more variable per unit of product due to the lower yield for most organic crops. For livestock, ruminant production systems tend to be more energy efficient under organic management due to the production of forage in grass–clover leys. Conversely, organic poultry tend to perform worse in terms of energy use as a result of higher feed conversion ratios and mortality rates compared to conventional fully housed or free-range systems. With regard to energy sources, there is some evidence that organic farms use more renewable energy and have less of an impact on natural ecosystems. Human energy requirements on organic farms are also higher as a result of greater system diversity and manual weed control. Overall this review has found that most organic farming systems are more energy efficient than their conventional counterparts, although there are some notable exceptions.

Laurence G. Smith, Adrian G. Williams* and Bruce. D. Pearce