Short Communication Pyrogenic carbon quantity and quality unchanged after 55 years of organic matter depletion in a Chernozem Nadezda A. Vasilyeva a, c, * , Samuel Abiven b , Evgeniy Y. Milanovskiy a , Michael Hilf b , Oleg V. Rizhkov d , Michael W.I. Schmidt b a Department of Soil Physics and Amelioration, Moscow State University named after M.V. Lomonosov, Moscow, Russia b Department of Geography, University of Zurich, Zurich, Switzerland c CNRS, UMR Bioemco, Soil Organic Matter Group, Thiverval-Grignon, France d State Central-Chernozem Natural Biosphere Reserve named after V.V. Alekhin, Kursk, Russia article info Article history: Received 14 January 2011 Received in revised form 17 May 2011 Accepted 21 May 2011 Available online 17 June 2011 Keywords: Black carbon Stable carbon Organic matter stabilization Benzene polycarboxylic acids abstract Chernozems typically have large stocks of organic carbon and of fire-derived, pyrogenic carbon (PyC). PyC had been considered to be slowly released but new results challenged this assumption, indicating that PyC can be lost within decades. We analyzed total soil organic carbon and PyC content (detectable as benzene polycarboxylic acids) in bulk samples, light and heavy fractions from a 55 year old bare fallow and a nearby steppe soil. Loss of PyC stock due to the long-term fallow management was much smaller (6%) than for soil organic carbon (33%), and we detected no changes in the degree of aromatic condensation of PyC. Most (70%) of the PyC was associated with the heavy fraction, and less with the light fraction (30%) pointing to organo-mineral interactions as important stabilizing processes. Ó 2011 Elsevier Ltd. All rights reserved. Pyrogenic carbon (PyC) is a residue of incomplete biomass combustion, and has been found in many soils, especially in Cherno- zems (Rodionov et al., 2010; Schmidt and Noack, 2000), with fire suspected to act as a soil forming factor (Eckmeier et al., 2007). Chernozems are known to store large amounts of organic carbon, even upon long cultivation (Kovda and Samoilova, 1983), and the presence of PyC might contribute to carbon stabilization. Soil PyC had been long considered as chemically inert (Skjemstad et al., 1996; Glaser et al., 2000; Schmidt and Noack, 2000), but new evidence suggest that PyC can be lost. Short-term lab incubations detected some initial mineralization of PyC (Hamer et al., 2004; Kuzyakov et al., 2009; Zimmerman, 2010) or physical transport within the soil profile (Guggenberger et al., 2008), or preferential erosion (Rumpel et al., 2006). Within 100 years a steppe Chernozem lost 25% of its initial PyC stocks (Hammes et al., 2008). For the newly formed PyC even higher decomposition rates are reported. Thus, in savanna soil half-life time of PyC was estimated to be less than 100 years (Bird et al., 1999), while in soils cleared from forest by fire losses of 70% were detected in the first 30 years (Nguyen et al., 2008). However, most studies focused on chemical structure and stabilization processes of PyC, and there are only very few studies that investigated its stability in long-term field conditions. Stabilization processes include interaction of oxidized PyC with minerals (Brodowski et al., 2005; Cheng et al., 2006; Cheng and Lehmann, 2009; Knicker et al., 2006), which enhance occlusion and thus co-stabilizes soil organic carbon in clay-size fractions (Brodowski et al., 2006). Both the rates of change and the mechanisms controlling the fate of soil PyC are still poorly understood. Here we tested the effect of 55 years of extreme organic matter depletion (i.e. bare fallow) on PyC quantity and quality in a Chernozem. To estimate the long-term stability of PyC, we took advantage of an existing field experiment in the State Central Chernozem Reserve (Streletzkaya steppe, Kursk, Russia) established in the 1935.Since 1626 this territory was reserved for hay harvest and pasture that implied fire suppression regime (Kabanova, 2004). Prior to this date wildfires occurred frequently in the forest-steppes. In 2003 we sampled a site under native steppe and an adjacent bare fallow soil, plowed twice a year to 22e24 cm depth since 1947. These cherno- zems (Haplicchernozem in FAO) developed on 2 m fine-silty loess * Corresponding author. CNRS, UMR Bioemco, Soil Organic Matter Group, Campus de Grignon, 78850 Thiverval-Grignon, France. Tel.: þ33 631660866; fax þ33 130815497. E-mail addresses: nadezda.vasilyeva@grignon.inra.fr (N.A. Vasilyeva), samuel. abiven@geo.uzh.ch (S. Abiven), eym@ps.msu.ru (E.Y. Milanovskiy), michael.hilf@ geo.uzh.ch (M. Hilf), ryzhkov@zapoved.kursk.ru (O.V. Rizhkov), michael.schmidt@ geo.uzh.ch (M.W.I. Schmidt). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2011.05.015 Soil Biology & Biochemistry 43 (2011) 1985e1988