Pedobiologia 51 (2008) 359—366 Charcoal and smoke extract stimulate the soil microbial community in a highly weathered xanthic Ferralsol $ Christoph Steiner a,Ã,1 , Keshav C. Das b , Marcos Garcia c , Bernhard Fo ¨rster d , Wolfgang Zech a a Institute of Soil Science and Soil Geography, University of Bayreuth, Postfach 10 1251, 95440 Bayreuth, Germany b Biorefining and Carbon Cycling Program, Faculty of Engineering, The University of Georgia, Athens, GA 30606, USA c Embrapa Amazonia Ocidental, CP 319-69011-970 Manaus, Brazil d ECT Oekotoxikologie GmbH, 65439 Flo ¨rsheim/Main, Germany Received 1 December 2006; received in revised form 16 August 2007; accepted 16 August 2007 KEYWORDS Bio-oil; Brazil; Microbial activity; Slash and char; Terra Preta; Wood vinegar Summary The influence of charcoal and smoke condensates (pyroligneous acid, PA) on microbial activity in a highly weathered Amazonian upland soil was assessed via measurements of basal respiration (BR), substrate-induced respiration (SIR), and exponential population increase after substrate addition. PA extracts are commonly used for fertilizer or as pest control in Brazil, where phosphorus (P) availability and nitrogen (N) leaching are among the most severe limitations for agriculture. Microbes play an important role in nutrient cycling and solubilizing of phosphate. BR, microbial biomass, population growth and the microbe’s efficiency (expressed by the metabolic quotient) increased linearly and significantly with increasing charcoal concentrations (50, 100 and 150 g kg 1 soil). Application of PA caused a sharp increase in all parameters. We suppose that the condensates from smoke contain easily degradable substances and only small amounts of inhibitory agents, which could be utilized by the microbes for their metabolism. & 2007 Elsevier GmbH. All rights reserved. Introduction In many parts of Brazil charcoal or carbonized biomass (rice hulls) are used in agriculture (Steiner et al., 2004b) and distillation of the pyroligneous acid (PA) fraction is often part of the ARTICLE IN PRESS www.elsevier.de/pedobi 0031-4056/$ - see front matter & 2007 Elsevier GmbH. All rights reserved. doi:10.1016/j.pedobi.2007.08.002 $ Embrapa Amazonia Ocidental, CP 319–69011-970 Manaus, Brazil. Ã Corresponding author. Tel./fax: +43 62175449. E-mail address: Christoph.Steiner@uni-bayreuth.de (C. Steiner). 1 Present address: Taxach 2, 5163 Mattsee, Austria.