Nitrogen Isotope Composition of Organically and Conventionally Grown Crops

Alison S. Bateman,† Simon D. Kelly,*†§ and Mark Woolfe#
School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom; Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, United Kingdom; and Food Standards Agency, Aviation House, 125 Kingsway, London WC2B 6NH, United Kingdom
J. Agric. Food Chem., 2007, 55 (7), pp 2664–2670
DOI: 10.1021/jf0627726
Publication Date (Web): March 7, 2007
Copyright © 2007 American Chemical Society
Food and Feed Chemistry

Abstract

Authentic samples of commercially produced organic and conventionally grown tomatoes, lettuces, and carrots were collected and analyzed for their δ15N composition in order to assemble datasets to establish if there are any systematic differences in nitrogen isotope composition due to the method of production. The tomato and lettuce datasets suggest that the different types of fertilizer commonly used in organic and conventional systems result in differences in the nitrogen isotope composition of these crops. A mean δ15N value of 8.1‰ was found for the organically grown tomatoes compared with a mean value of −0.1‰ for those grown conventionally. The organically grown lettuces had a mean value of 7.6‰ compared with a mean value of 2.9‰ for the conventionally grown lettuces. The mean value for organic carrots was not significantly different from the mean value for those grown conventionally. Overlap between the δ15N values of the organic and conventional datasets (for both tomatoes and lettuces) means that it is necessary to employ a statistical methodology to try and classify a randomly analyzed “off the shelf” sample as organic/conventional, and such an approach is demonstrated. Overall, the study suggests that nitrogen isotope analysis could be used to provide useful “intelligence” to help detect the substitution of certain organic crop types with their conventional counterparts. However, δ15N analysis of a “test sample” will not provide unequivocal evidence as to whether synthetic fertilizers have been used on the crop but could, for example, in a situation when there is suspicion that mislabeling of conventionally grown crops as “organic” is occurring, be used to provide supporting evidence.

Keywords: Nitrogen; isotope; organic; conventional; δ15N

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History

  • Published In Issue April 04, 2007
  • Received for review September 27, 2006. Revised manuscript received January 8, 2007. Accepted January 25, 2007. This work was financed by the U.K. Food Standards Agency as part of its Food Authenticity and Labelling Programme, Project Q01076. The views expressed in this paper are those of the authors and do not necessarily reflect the views of the U.K. Food Standards Agency.

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