Energy Analysis of Organic and Conventional Agricultural Systems

Abstract

Energy parameters of a Swedish long-term field experiment comparing organic and conventional agricultural systems were evaluated. There is great potential for misinterpretation of system comparisons as a result of choice of data and how energy data are expressed. For example, reported yields based on single crops and not the whole rotation can result in significantly different interpretations. Energy use per unit yield was lower in organic crop and animal production than in the corresponding conventional system, as previously found in other studies. This is due to the exclusion of N fertiliser, the largest energy input in conventional cropping systems. Energy use per unit yield expresses system efficiency, but the term is insufficient to evaluate the energy characteristics of agricultural systems. Calculation of the most important energy component, net energy production per unit area, showed that conventional systems produced far more energy per hectare than organic systems. The energy productivity (output/input ratio), i.e. the energy return on inputs, was at least six in both types of agriculture, revealing the highly positive energy balance of crop production in general. Lower yields in the organic systems, and consequently lower energy production per unit area, mean that more land is required to produce the same amount of energy. This greater land requirement in organic production must be considered in energy balances. When the same area of land is available for organic and conventional crop production, the latter allows for complementary bio-energy production and can produce all the energy required for farming, such as fuels, N fertilisers, etc., in the form of ethanol. In a complete energy balance, options such as combustion, gasification or use as fodder of protein residues from ethanol production must also be taken into account. There is a common belief that the high fossil fuel requirement in N fertiliser production is non-sustainable. This is a misconception, since the use of N fertilisers provides a net energy gain. If N fertilisers were to be completely replaced by biological N2 fixation, net energy production would be significantly lower. In addition, N fertiliser production can be based on renewable energy sources such as bio-fuels produced by gasification. Conventional crop production is thus energetically fully sustainable. Energy analyses of agricultural systems presented in this chapter illustrate that published data may require recalculation in relation to the background, prevailing trends and boundary conditions, and subsequent re-interpretation. New perspectives on energy use must also be considered.