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Macroaggregation and soil organic carbon restoration in a highly weathered Brazilian Oxisol after two decades under no-till

De Oliveira Ferreira A., De Moraes Sa J.C., Lal R., Tivet F., Briedis C., Massao Inagaki T., Potma Gonçalves D.R., Romaniw J.. 2018. Science of the Total Environment, 621 : p. 1559-1567.

DOI: 10.1016/j.scitotenv.2017.10.072

Conclusions based on studies of the impacts of soil organic carbon (SOC) fractions and soil texture on macroaggregation and SOC stabilization in long-term (> 20 years) no-till (NT) fields remain debatable. This study was based on the hypothesis that the amount and frequency of biomass-C input associated with NT can be a pathway to formation of macroaggregates and to SOC buildup. The objectives were to: 1) assess the macroaggregate distribution (proportional mass, class mass) and the SOC and particulate organic carbon (POC) stocks of extra-large (8¿19 mm), large (2¿8 mm) and small (0.25¿2 mm) macroaggregate size classes managed for two decades by NT, and 2) assess the recovery of SOC stocks in extra-large macroaggregates compared to adjacent native vegetation (Andropogon sp., Aristida sp., Paspalum sp., and Panicum sp.). The crop rotation systems were: soybean (Glycine max L.), maize (Zea mays L.) and beans (Phaseolus vulgaris L.) in summer; and black oat (Avena strigosa Schreb), white oat (Avena sativa), vetch (Vicia sativa L.), black oat. + vetch (Avena strigosa Schreb + vetch) and wheat (Triticum aestivum L.) in winter. The experimental was laid out as 2 × 2 randomized block factorial with 12 replicates of a NT experiment established in 1997 on two highly weathered Oxisols. The factors comprised of: (a) two soil textural types: clay loam and sandy clay, and (b) two sampling depths: 0¿5 and 5¿20 cm. The three classes of macroaggregates were obtained by wet sieving, and the SOC content was determined by the dry combustion method. The extra-large macroaggregate classes in 0¿20 cm depth for sandy clay (SdC) and clay loam (CL) Oxisol represented 75.2 and 72.4% of proportional mass, respectively. The SOC and POC stocks among macroaggregate classes in 0¿5 and 5¿20 cm depths decreased in the order: 8¿19 mm > 2¿8 mm ¿ 0.25¿2 mm. The SdC plots under soybean/maize at 3:1 ratio recovered 58.3%, while those at 1:1 ratio (high maize frequency) in CL recovered 73.1% of SOC stock in the extra-large macroaggregates compared with the same under native vegetation for 0¿20 cm depth. Thus, partial restoration of the SOC stock in original extra-large macroaggregate confirms the hypothesis that NT through higher maize cultivation frequency can be a pathway to fomation of macroaggregates and SOC buildup.

Mots-clés : sol tropical; texture du sol; récupération des sols; matière organique du sol; teneur en matière organique; travail du sol; non-travail du sol; séquestration du carbone; modèle mathématique; brésil; parana

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