Isotopic discrimination as a tool for organic farming certification in sweet pepper

Organic farming is a form of agriculture that excludes the use of synthetic fertilizers, pesticides, and genetically modified organisms. These fertilizers have been traditionally overused in conventional farming to avoid lost revenue, but this often not does not take into account the potential contamination of aquifers and river due to nitrate leaching. Transition to organic farming practices could provide an instrument to reduce contamination and increase potential income. It is difficult to determine to what extent those fertilizers could have been used within a complete traceability of the production process. In this experiment, we evaluated the use of N-15/N-14 isotopic discrimination in sweet pepper plants to test the hypothesis that synthetic fertilizers significantly reduce N-15/N-14 compared with exclusively organic practices. Therefore, three common types of organic manures (sheep, hen, or horse) were applied at a rate of 8 kg m(-2) with or without synthetic fertilizer amendments under fully controlled environmental and irrigation conditions. Results indicate that (i) use of synthetic fertilizers significantly reduced (15/14)N(2)vsN(2)atm compared with treatments that only received water; (ii) with respect to the plant organs, old leaves and fruits were more sensitive to the synthetic fertilizer additions with reductions in (15/14)N(2)vsN(2)atm of 24.1 and 27.8%, respectively; and (iii) independently of the organic manure used, no additional fertilization (synthetic or organic) is required before 106 days after transplanting at that dosage because plant fresh weight was not reduced.