Posted by: Mahdi Ebrahimi | February 2, 2008

New Method Detects Fraud in Organically Grown Produce

As organic farming becomes more common, methods to identify fraud in the industry are increasingly important. In a recent study in Journal of Environmental Quality, scientists successfully use nitrogen isotopic discrimination to determine if non-organic, synthetic fertilizers were used on sweet pepper plants.

Scientists at the Instituto Murciano de Investigación y Desarrollo Agrario y Agrario y Alimentario (IMIDA) jointly with the Instituto de Agrobiotecnología (UPNA-CSIC), in Spain, investigated the use of isotopic discrimination in organic crops to detect if chemical Nitrogen (N) fertilizers were added, in a new study. Specifically, they measured 15N-abundance variations in sweet pepper plants with three common manures, with or without the addition of chemical fertilizers during the crop cycle.

Francisco del Amor, who conducted the study, said that “isotopic discrimination has demonstrated that we can successfully identify fraud if synthetic N fertilizers are used in the organic production of sweet peppers; however, further studies including the effects of different soil characteristics, climate, and biotic or abiotic stress could be useful in determining the proper interval of 15N-values to exclude non-organic fertilization practices for certification policies.”

15N abundance in the atmosphere, the largest N reserve in the world, remains constant around the planet. However, several physical, chemical, and biological processes and reactions implicated in the synthesis and transformation of organic compounds present different affinities for 15N or 14N isotopes. Due to this discrimination, products resulting from these reactions are usually enriched or impoverished in 15N in comparison with the original.

The N in synthetic N fertilizers is derived from atmospheric N2, and this process results in little change in the original atmospheric N isotope ratio but, by contrast, nitrate derived from animal manures (typically used in organic farming) can have greater values signifying a 15N enrichment above the original 15N/14N ratio in starting N2. This is significantly different from the fertilizer N isotopic value, and plants grown with different fertilizer sources of N can be identified.

15N-values (stable isotope abundances expressed as the relative difference of the isotope ratio from that of an international standard in parts per thousand), were determined in sweet pepper plants under controlled ambient and soil conditions in a greenhouse. Leaves (young and old), stems, roots and fruits were analyzed in plants cultivated organically or with synthetic fertilizer amendments. Therefore, three types of animal manures (sheep, hen or horse) were applied at preplanting, and during the crop cycle half of the plants in each manure zone received only water, and the other plants received chemical fertilizers as commonly used in conventional cultivation.

The results of this study showed that:

  1. use of synthetic fertilizers significantly reduced 15/14N2vsN2atmosphere compared with treatments that only received water;
  2. with respect to the plant organs, old leaves and fruits were more sensitive to the synthetic fertilizer additions with reductions in 15/14N2vsN2atm of 24.1 and 27.8%, respectively; and
  3. independently of the organic manure used, no additional fertilization (synthetic or organic) was required before 106 days after transplanting with the common dosage of manure, as plant fresh weight was not reduced.

Results from the study were published in the January-February issue of the Journal of Environmental Quality. The research was also presented in Naples, Italy, at the GreenSys2007 Symposium of the International Society for Horticultural Science in October 2007. Funding was provided by the Fundación Séneca de la Región de Murcia.

Adapted from materials provided by American Society of Agronomy.




  1. […] New Method Detects Fraud in Organically Grown Produce […]

  2. NEWS RELEASE, 3 JULY 2008

    A senior researcher at GNS Science is using a novel test that can verify if vegetables in the supermarket have been grown organically.

    Karyne Rogers of GNS Science’s Stable Isotope Laboratory in Lower Hutt said the method was an inexpensive way to verify the organic status of vegetables by distinguishing between vegetables grown with organic or industrially made fertilisers.

    A criteria in growing organic vegetables is that only organic fertiliser, usually animal manure, is used. As vegetables grow, they incorporate nitrogen from the fertiliser and it is this nitrogen which is analysed. The nitrogen isotope signatures of animal manure and industrial fertiliser are quite different.

    “It’s an independent check on the growing regime. As far as I am aware, this is the first simple reliable test for organic vegetables in New Zealand,” Dr Rogers said. “Consumers need independent checks for produce that cost significantly more because of its label.”

    Clients can obtain results within 10 days of submitting samples, and the test can be done at any stage during vegetable growth. This method can also determine if vegetables are grown hydroponically, or naturally in soil.

    A similar isotope technique using carbon can be used to determine if vegetables, such as tomatoes, have been grown in a greenhouse heated by fossil fuels.

    Dr Rogers said these new tests were an extension of the food testing that the Stable Isotope Laboratory has been doing for the past 12 years.

    “Since 1996 we have been testing orange juice for the beverage industry to determine if sugar or tap water has been added.”

    “We also offer a test for the honey industry to determine if bees have been fed sugar or if glucose has been added to increase the volume of the honey.”

    Dr Rogers’ team is developing isotope-based tests that would determine if produce labelled “NZ Grown” was in fact grown in New Zealand.

    Isotope analysis techniques offered the food industry a quick and reliable way to boost the confidence in labelling, Dr Rogers said.

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