Influence of N doses and form on 15 N natural abundance of pepper plants: considerations for using δ 15 N values as indicator of N source

BACKGROUND: The aim of this study was to ascertain the effect of the N form (NO 3 − , NH 4 + and organic N) and N concentration on plant isotopic fractionation and on the contribution of the different N sources to the plant N budget, in order to evaluate the feasibility of using plant δ 15 N values for discriminating between conventional and organic crops. To this end, different N concentrations (applied as NO 3 − ), N forms (NO 3 − versus NH 4 + ), and increasing NO 3 − applications to an organic N‐based fertilization regime were studied. RESULTS: When using NO 3 − as N source, intra‐plant fractionation was significant and tended to increase when NO 3 − concentration increased in the root medium. However, negligible net isotopic fractionation was observed when comparing theoretical and measured plant δ 15 N values. On the other hand, when plants are fertilized with a mixture of NO 3 − and NH 4 + , differences in uptake patterns for both salts could result in variation in plant δ 15 N regarding to the expected value. Finally, the application of NO 3 − to plants was detected when it was combined with high levels of organic N sources, from 99:1 organic:inorganic N ratio. CONCLUSION: Under certain conditions and following some considerations concerning sampling, δ 15 N values can be considered to be a potential tool to guarantee the authenticity of organic products. Copyright © 2011 Society of Chemical Industry