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New method detects fraud in organically grown produce

As organic farming becomes more common, methods to identify fraud in the industry are increasingly important.

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

“Isotopic discrimination has demonstrated that we can successfully identify fraud if synthetic nitrogen fertilizers are used in the organic production of sweet peppers,” said Francisco del Amor, who conducted the study. “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.”

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

During the study, 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.

Three types of animal manures (sheep, hen or horse) were applied at pre-planting and, during the crop cycle, half of the plants in each manure zone received only water while the other plants received chemical fertilizers commonly used in conventional cultivation.The results of this study showed that:

·       use of synthetic fertilizers significantly reduced 15/14N₂ versus N₂ (atmosphere) compared with treatments that only received water;

·       with respect to the plant organs, old leaves and fruits were more sensitive to the synthetic fertilizer additions with reductions in 15/14N₂ versus N₂ (atmosphere) of 24.1 and 27.8 per cent, respectively; and

·       independent 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.