Organic vs. Conventional Grassland Management: Do

Distinguishing organic and conventional products is a major issue of food security and authenticity. Previous studies successfully used stable isotopes to separate organic and conventional products, but up to now, this approach was not tested for organic grassland hay and soil. Moreover, isotopic abundances could be a powerful tool to elucidate differences in ecosystem functioning and driving mechanisms of element cycling in organic and conventional management systems. Here, we studied the dN and dC isotopic composition of soil and hay samples of 21 organic and 34 conventional grasslands in two German regions. We also used DdN (dN plant dN soil) to characterize nitrogen dynamics. In order to detect temporal trends, isotopic abundances in organic grasslands were related to the time since certification. Furthermore, discriminant analysis was used to test whether the respective management type can be deduced from observed isotopic abundances. Isotopic analyses revealed no significant differences in dC in hay and dN in both soil and hay between management types, but showed that dC abundances were significantly lower in soil of organic compared to conventional grasslands. DdN values implied that management types did not substantially differ in nitrogen cycling. Only dC in soil and hay showed significant negative relationships with the time since certification. Thus, our result suggest that organic grasslands suffered less from drought stress compared to conventional grasslands most likely due to a benefit of higher plant species richness, as previously shown by manipulative biodiversity experiments. Finally, it was possible to correctly classify about two third of the samples according to their management using isotopic abundances in soil and hay. However, as more than half of the organic samples were incorrectly classified, we infer that more research is needed to improve this approach before it can be efficiently used in practice. Citation: Klaus VH, Hölzel N, Prati D, Schmitt B, Schöning I, et al. (2013) Organic vs. Conventional Grassland Management: Do N and C Isotopic Signatures of Hay and Soil Samples Differ? PLoS ONE 8(10): e78134. doi:10.1371/journal.pone.0078134 Editor: Shuijin Hu, North Carolina State University, United States of America Received July 9, 2013; Accepted September 14, 2013; Published October 25, 2013 Copyright: 2013 Klaus et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The work has been funded by the DFG Priority Program 1374 ‘‘Infrastructure-Biodiversity-Exploratories’’ (FI 1246/6-1, FI1246/9-1, HO 3830/2-2, SCHR 1181/2-1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: [email protected]