nvironmental impact assessment of conventional and organic milk production *

Organic agriculture addresses the public demand to diminish environmental pollution of agricultural production. Until now, however, only few studies tried to determine the integrated environmental impact of conventional versus organic production using life cycle assessment (LCA). The aim of this article was to review prospects and constraints of LCA as a tool to assess the integrated environmental impact of conventional and organic animal production. This aim was illustrated using results from LCAs in the literature and from a pilot study comparing conventional and organic milk production. This review shows that LCAs of different case studies currently cannot be compared directly. Such a comparison requires further international standardisation of the LCA method. A within-case-study comparison of LCAs of conventional and organic production, however, appeared suitable to gain knowledge and to track down main differences in potential environmental impact. Acidification potential of milk production, for example, is for 78–97% due to volatilisation of ammonia, which is not reduced necessarily by changing from conventional to organic milk production. Eutrophication potential per tonne of milk or per ha of farmland was lower for organic than for conventional milk production due to lower fertiliser application rates. Global warming potential of milk production is for 48–65% due to emission of methane. Organic milk production inherently increases methane emission and, therefore, can reduce global warming potential only by reducing emission of carbon dioxide and nitrous oxide considerably. Organic milk production reduces pesticide use, whereas it increases land use per tonne of milk. Conclusions regarding potential environmental impact of organic versus conventional milk production, however, are based largely on comparison of experimental farms. To show differences in potential environmental impact among various production systems, however, LCAs should be performed at a large number of practical farms for each production system of interest. Application of LCA on practical farms, however, requires in-depth research to understand underlying processes, and to predict, or measure, variation in emissions realised in practice.  2002 Published by Elsevier Science B.V.