The impact of soil management on aggregation, carbon stabilization and carbon loss as CO 2 in the surface layer of a Rhodic Ferralsol in Southern Brazil Renata C. Barreto a , Beata E. Madari b, *, John E.L. Maddock a , Pedro L.O.A. Machado b , Eleno Torres c , Julio Franchini c , Adriana R. Costa a a Department of Geochemistry, Institute of Chemistry, Fluminense Federal University, Outeiro Sa ˜o Joa˜o Baptista, s/n., CEP 24020-141, Nitero ´i, RJ, Brazil b Embrapa Rice and Beans, Rod. GO-462, km 12, P.O. Box 179, CEP 75375-000, Santo Antoˆnio de Goia ´s, GO, Brazil c Embrapa Soybean, Rod. Carlos Joa ˜o Strass - Distrito de Warta, P.O. Box 231, CEP 86001-970, Londrina, PR, Brazil 1. Introduction The greenhouse effect, an essential natural process on Earth has been accentuated by anthropogenic activities, which have increased the concentrations of naturally occurring greenhouse gases (GHGs) in the atmosphere, and introduced others. Carbon dioxide (CO 2 ) is the principal gas responsible for the anthropogenic greenhouse gas effect because of the quantity emitted by fuel combustion and deforestation. However, other land use practices offer the possibility of diminished emission or sequestration of CO 2 (Perlack et al., 1992– 1993; Guo and Gifford, 2002; Shaoqiang et al., 2004). Tropical and sub-tropical geographical regions make important contributions to GHG emissions to the atmosphere (Mosier et al., 2004). Data by the International Panel on Climate Change (Watson et al., 2000) shows that approximately 1.7 Gt year 1 (corresponds to 21% of total emissions) originates from land use changes, and Brazil is the largest emitter of these GHGs. On the other hand, soils of terrestrial ecosystems can sequester approximately 1.9 Gt year 1 of carbon from the atmosphere under adequate management systems. Part of the CO 2 is temporarily removed from the atmosphere by photo- synthesis and respiration of plants, and by accumulation of carbon in the soil (Houghton, 2007). Agriculture, Ecosystems and Environment 132 (2009) 243–251 ARTICLE INFO Article history: Received 28 July 2008 Received in revised form 7 April 2009 Accepted 14 April 2009 Available online 12 May 2009 Keywords: No-tillage Conventional tillage Soil aggregation Total organic carbon Soil incubation CO 2 emission ABSTRACT Soil aggregation and organic carbon accumulation are two intrinsically linked phenomena. Soils under natural vegetation and conservation tillage systems generally have higher aggregation indices and total organic carbon (TOC) stocks in the surface layers than soils under conventional management (ploughing). From the point of view of the emission of carbon dioxide (CO 2 ), C stabilization and loss in the surface layer is relevant. The objective of this study was to investigate the effect of no-tillage (NT) and conventional tillage (CT) on TOC stabilization and loss through soil aggregation in the topsoil. Soil aggregation, TOC stocks, and fluxes of CO 2 of samples from a Rhodic Ferralsol under NT and CT in a long-term field experiment in Southern Brazil were measured. A natural forest site was also evaluated as reference to the management sites. Emissions of CO 2 were measured in laboratory incubation experiment on bulk soil samples and on soil aggregate size fractions, previously separated by dry sieving, in intact and destroyed (crushed to <0.250 mm) state. The soil under NT had larger aggregates and larger proportion of the soil in greater aggregate size classes than CT. Total organic carbon stocks were higher under NT both in bulk soil samples and macroaggregates than under CT. Under laboratory conditions the bulk soil samples from NT showed higher emission rates of CO 2 (CO 2BS = 18.3 kg C ha 1 h 1 ) than from CT (CO 2BS = 2.3 kg C ha 1 h 1 ) due to the overall higher TOC stocks. The TOC that was lost by CO 2 emission due to the oxidation of readily decomposable macroaggregate-protected SOM in NT (SDCO 2 = 79.4 kg C ha 1 h 1 ) was, however, also higher than under CT (CT: SDCO 2 = 29.1 kg C ha 1 h 1 ). The TOC stabilized by macroaggregation in NT was also more than the TOC lost by CO 2 emission from the bulk soil (SDCO 2 -CO 2BS = 61.1 kg C ha 1 h 1 ), and the difference between these two was higher under NT than under CT (SDCO 2 -CO 2BS = 26.8 kg C ha 1 h 1 ), showing that NT in fact accumulates more TOC in the soil by protecting it within the macroaggregates. The natural forest had higher TOC stock and emission rates than the tilled soils, however it also stabilized more TOC. Thus, no-tillage in its effect on carbon stabilization, is between the natural ecosystem and CT, representing a soil management system that seems to be an efficient on the way path to the recuperation of soil after conventional management systems. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author at: Embrapa Rice and Beans, Rod. GO-462, km 12, Caixa Postal 179, CEP 75375-000, Santo Anto ˆnio de Goia ´ s, GO, Brazil. Tel.: +55 62 3533 2181; fax: +55 62 3533 2100. E-mail address: madari@cnpaf.embrapa.br (B.E. Madari). Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee 0167-8809/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2009.04.008