Organic vs. Conventional Grassland Management: Do 15N and 13C Isotopic Signatures of Hay and Soil Samples Differ?

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 δ15N and δ13C isotopic composition of soil and hay samples of 21 organic and 34 conventional grasslands in two German regions. We also used Δδ15N (δ15N plant - δ15N 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 δ13C in hay and δ15N in both soil and hay between management types, but showed that δ13C abundances were significantly lower in soil of organic compared to conventional grasslands. Δδ15N values implied that management types did not substantially differ in nitrogen cycling. Only δ13C 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.

[1]  R Core Team,et al.  R: A language and environment for statistical computing. , 2014 .

[2]  M. Lange,et al.  Does organic grassland farming benefit plant and arthropod diversity at the expense of yield and soil fertility , 2013 .

[3]  S. Boch,et al.  Direct and productivity‐mediated indirect effects of fertilization, mowing and grazing on grassland species richness , 2012 .

[4]  P. Högberg,et al.  Nitrogen isotopes link mycorrhizal fungi and plants to nitrogen dynamics. , 2012, The New phytologist.

[5]  Carsten F. Dormann,et al.  A quantitative index of land-use intensity in grasslands: Integrating mowing, grazing and fertilization , 2012 .

[6]  E. Schulze,et al.  Foliar and soil δ15N values reveal increased nitrogen partitioning among species in diverse grassland communities. , 2011, Plant, cell & environment.

[7]  M. R. Tabilio,et al.  Potential isotopic and chemical markers for characterising organic fruits , 2011 .

[8]  N. Wrage,et al.  Isotopic composition of soil, vegetation or cattle hair no suitable indicator of nitrogen balances in permanent pasture , 2011, Nutrient Cycling in Agroecosystems.

[9]  Jens Nieschulze,et al.  Implementing large-scale and long-term functional biodiversity research: The Biodiversity Exploratories , 2010 .

[10]  David Kleijn,et al.  Effect of conservation management on bees and insect-pollinated grassland plant communities in three European countries , 2010 .

[11]  N. Buchmann,et al.  Relating plant species and functional diversity to community δ13C in NE Spain pastures , 2009 .

[12]  J. Molkentin.  Authentication of organic milk using delta13C and the alpha-linolenic acid content of milk fat. , 2009, Journal of agricultural and food chemistry.

[13]  W. Wanek,et al.  Foliar δ15N values characterize soil N cycling and reflect nitrate or ammonium preference of plants along a temperate grassland gradient , 2008, Oecologia.

[14]  J. Navarro,et al.  Isotopic discrimination as a tool for organic farming certification in sweet pepper. , 2008, Journal of environmental quality.

[15]  S. Kelly,et al.  Fertilizer nitrogen isotope signatures , 2007, Isotopes in environmental and health studies.

[16]  Federica Camin,et al.  Evaluation of markers for the traceability of potato tubers grown in an organic versus conventional regime , 2007 .

[17]  S. Kelly,et al.  Nitrogen isotope composition of organically and conventionally grown crops. , 2007, Journal of agricultural and food chemistry.

[18]  W. Wanek,et al.  Natural 15N abundance of plants and soils under different management practices in a montane grassland , 2006 .

[19]  P. Högberg,et al.  Winners and losers in herbaceous plant communities: insights from foliar carbon isotope composition in monocultures and mixtures , 2005 .

[20]  A. Rossmann,et al.  Multielement Isotope Ratios of Vegetables from Integrated and Organic Production , 2005, Plant and Soil.

[21]  K. Auerswald,et al.  Carbon and nitrogen stable isotope composition of cattle hair: ecological fingerprints of production systems? , 2005 .

[22]  Olaf Schmidt,et al.  Inferring the origin and dietary history of beef from C, N and S stable isotope ratio analysis , 2005 .

[23]  S. Kelly,et al.  Nitrogen isotope relationships between crops and fertilizer: implications for using nitrogen isotope analysis as an indicator of agricultural regime. , 2005, Journal of agricultural and food chemistry.

[24]  Michael Kreuzer,et al.  Geographic origin of meat—elements of an analytical approach to its authentication , 2005 .

[25]  Paolo Rapisarda,et al.  Nitrogen metabolism components as a tool to discriminate between organic and conventional citrus fruits. , 2005, Journal of agricultural and food chemistry.

[26]  Jeremy D. Wilson,et al.  Does organic farming benefit biodiversity , 2005 .

[27]  B. Glaser,et al.  Short-term sequestration of slurry-derived carbon into particle size fractions of a temperate grassland soil , 2004, Isotopes in environmental and health studies.

[28]  A. Nakano,et al.  Effect of organic and inorganic fertigation on yields, δ15N values, and δ13C values of tomato (Lycopersicon esculentum Mill. cv. Saturn) , 2003, Plant and Soil.

[29]  P. Högberg,et al.  Studies of 13C in the foliage reveal interactions between nutrients and water in forest fertilization experiments , 1993, Plant and Soil.

[30]  H. Förstel,et al.  Stable isotope variation as a tool to trace the authenticity of beef , 2004, Analytical and bioanalytical chemistry.

[31]  Christina Gloeckner,et al.  Modern Applied Statistics With S , 2003 .

[32]  R. Amundson,et al.  Turnover and storage of C and N in five density fractions from California annual grassland surface soils , 2002 .

[33]  Brian D. Ripley,et al.  Modern Applied Statistics with S Fourth edition , 2002 .

[34]  R. Ryel,et al.  Mechanisms of positive biodiversity–production relationships: insights provided by δ13C analysis in experimental Mediterranean grassland plots , 2001 .

[35]  M. Adams,et al.  Stable Isotopes at Natural Abundance in Terrestrial Plant Ecology and Ecophysiology: An Update , 2001 .

[36]  W. Brand,et al.  Referencing strategies and techniques in stable isotope ratio analysis. , 2001, Rapid communications in mass spectrometry : RCM.

[37]  G. Haas,et al.  Comparing intensive, extensified and organic grassland farming in southern Germany by process life cycle assessment , 2001 .

[38]  J. Dyckmans,et al.  Nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange and water use efficiency in winter wheat. , 2000, Environmental and experimental botany.

[39]  H. Šantrůčková,et al.  Microbial processes and carbon‐isotope fractionation in tropical and temperate grassland soils , 2000 .

[40]  C. Scrimgeour,et al.  Stable isotope natural abundances of soil, plants and soil invertebrates in an upland pasture , 1998 .