Nitrogen isotopes as a screening tool to determine the growing regimen of some organic and nonorganic supermarket produce from New Zealand

An isotopic study was performed on nine varieties of organically and conventionally grown vegetables from an organic food market and a chain supermarket in New Zealand. The main aim of the study was to assess the applicability of stable nitrogen isotopes as a screening tool to differentiate between organic and conventional growing conditions of various vegetable types sampled directly off supermarket shelves. This could be further used as the basis of a simple authentication tool to detect noncompliant organic farming practices and false labeling of organic produce. In this study, nitrogen isotopes are found to be an excellent way of identifying faster growing organic vegetables (maturity time to harvest of <80 days), as these vegetables tend to be significantly more enriched in (15)N than conventionally grown vegetables and natural soil N. For slower growing organic produce (maturity time to harvest of >80 days), more information would be required to understand isotopic variations and fractionation effects between vegetables and soil over time as the technique does not discriminate organic from conventional regimens for these vegetables with as much certainty.