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Soil carbon sequestration and mulch-based cropping in the Cerrado region of Brazil

Corbeels M., Scopel E., Cardoso A., Douzet J.M., Neto M.S., Bernoux M.. 2004. In : Turner Neil (ed.), Angus John (ed.), Mc Intyre Lynne (ed.), Robertson Michael (ed.), Borrell Andrew (ed.), Lloyd David (ed.). New directions for a diverse planet : Proceedings for the 4th International Crop Science Congress, Brisbane, Australia, 26 Sep - 1 Oct 2004. Gosford : Regional Institute, n.p.. International Crop Science Congress. 4, 2004-09-26/2004-10-01, Brisbane (Australie).

Direct seeding mulch-based cropping (DMC) systems have largely been adopted over the last 10 to 15 years in the Cerrado region of Brazil as a means to combat soil degradation. Continuous cropping and the absence of soil tillage under DMC favour the sequestration of C in soils. The objective of this study was to assess the soil C sequestration potential of the DMC systems in the Cerrados based on data from a chronosequence and simulation of soil C dynamics using the G'DAY plant-soil model that includes the CENTURY decomposition submodel. Soil C sequestration rate derived from linear regression of all soil C contents measured on a DMC chronosequence between age 0 and 12 in the upper 0-20 cm topsoil layer was 0.83 Mg/ha/yr. The corresponding change in soil total N was +79 kg/ha/yr. Model results indicate that C is lost at rates of about 1.25 Mg/ha/yr from the 0-40 cm soil layer after conversion of native vegetation to soybean or maize monocropping under conventional tillage for 30 years. In contrast, DMC systems with pearl millet as cover crop were adequate to maintain high soil C levels as under the native vegetation. This was largely attributed to the high net primary productivity (NPP) and relatively small removal of NPP as harvest. Gains in modeled C under DMC were sustained by increased N input and/or decreased N losses.

Mots-clés : propriété physicochimique du sol; carbone; mulch; paillage; brésil

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