Stable isotopes as a predictor for organic or conventional classification of berries and vegetables

• Published in: PloS one Vol. 20; no. 3; p. e0318179
• Main Authors: Zhu-Barker, Xia, Liou, Michael, Zapata, Diana, Huang, Jingyi, Horwath, William R.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 12.03.2025; Public Library of Science (PLoS)
• Subjects: Agricultural production; Agriculture; Berries; Biology and Life Sciences; Carbon; Carbon 13; Carbon content; Carbon Isotopes - analysis; Carbon/nitrogen ratio; Chemical properties; Classification; Crops; Crops, Agricultural - chemistry; Crops, Agricultural - classification; Farming; Fertilizers; Food; Food quality; Fruit - chemistry; Fruit - classification; Hypothesis testing; Identification and classification; Isotopes; Nitrates; Nitrogen; Nitrogen Isotopes - analysis; Organic Agriculture - methods; Organic farming; Organic fertilizers; People and places; Physical Sciences; Stable isotopes; Statistical models; Vegetables; Vegetables - chemistry; Vegetables - classification; United States; United States > US; Mexico; California
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0318179

Organic agriculture is expanding worldwide, driven by expectations of improving food quality and soil health. However, while organic certification by regulatory bodies such as the United States Department of Agriculture and the European Union confirms compliance with organic standards that prohibit synthetic chemical inputs, there is limited oversight to verify that organic practices, such as the use of authentic organic fertilizer sources, are consistently applied at the field level. This study investigated the elemental content of carbon (C) and nitrogen (N) and their stable isotopes (δ 13 C and δ 15 N) in seven different crops grown under organic or conventional practices to assess their applicability as a screening tool to verify the authenticity of organic labeled produce. Holm corrected Welch t-tests and a generalized linear mixed model (GLMM) were used to assess the potential of stable isotope or crop elemental content to differentiate organic vs. conventional production systems. Total C and N content or C/N ratio was not significantly different between production systems or among geographic origins for most crops. However, the average N stable isotope (δ 15 N) content differed, with conventional crops at 1.8 ± 2.2‰ and organic at 6.0 ± 3.4‰. A mixed model incorporating elemental contents and stable isotopes identified δ 15 N as the primary predictor in discriminating organic and conventional production systems. A δ 15 N threshold is suggested to differentiate conventional from organic grown raspberries (δ 15 N < 2.17‰) and strawberries (δ 15 N < 3.22‰), for an estimated false negative rate of 1%. Although further evaluation is needed, our extensive dataset (n = 791) captures key predictors of agricultural production systems and holds potential as a benchmark for future organic production verification.