Can δ15N in lettuce tissues reveal the use of synthetic nitrogen fertiliser in organic production?

BACKGROUND: The nitrogen isotopic fingerprint (δ15N) is reported to be a promising indicator for differentiating between organically and conventionally grown vegetables. However, the effect on plant δ15N of split nitrogen fertilisation, which could enable farmers to cover up the use of synthetic fertiliser, is not well studied. In this study the use of δ15N in lettuce as a potential marker for identifying the use of synthetic nitrogen fertiliser was tested on pot‐grown lettuce (Lactuca sativa L.) treated with synthetic and organic nitrogen fertilisers (single or split application). The effect of combined usage of synthetic and organic fertilisers on δ15N was also investigated. RESULTS: The δ15N values of whole plants treated with different fertilisers differed significantly when the fertiliser was applied in a single treatement. However, additional fertilisation (with isotopically the same or different fertiliser) did not cause a significant alteration of plant δ15N. CONCLUSION: The findings of the study suggest that the δ15N value of lettuce tissues could be used as a rough marker to reveal the history of nitrogen fertilisation, but only in the case of single fertiliser application. However, if the difference in δ15N between the applied synthetic and organic nitrogen fertilisers was > 9.1‰, the detection of split and combined usage of the fertilisers would have greater discriminatory power. Copyright © 2010 Society of Chemical Industry