Encapsulation of soil organic carbon (SOC) within aggregates is one of the principal mechanisms for long-term C sequestration, macroaggregate formation and stabilization. Our objectives were to quantify the changes in aggregate size distribution, aggregate-C concentrations and stocks upon conversion of native vegetation (NV) to conventional plow-based tillage (CT), and to assess the rate of aggregation and SOC recovery with no-till (NT) under diverse biomass-C inputs. The study was conducted at both sub-tropical (Ponta Grossa – PG, State of Parana´ ) and tropical (Lucas do Rio Verde – LRV, State of Mato Grosso) sites in Brazil. The SOC content under NV was used as a baseline to evaluate the depletion rate under CT and the restoration rate under NT. A speci?c emphasis was given to the largest macroaggregate size class (8– 19 mm) because of its importance to protecting the recently deposited labile SOC. A discriminant analysis of principal components (DAPC) indicated that NV soil is modi?ed by conversion to an arable land use and that, mechanical tillage, biomass input, and their interactions drastically in?uence the distribution of aggregate-size classes, aggregation indices, and SOC distribution within aggregates. At both sites, soil aggregation indices were positively impacted by NT and associated with SOC concentration in the labile fractions (e.g., total polysaccharides (TPS), hot water extractable organic C (HWEOC), particulate organic C (POC)). At the PG site, the 8–19 mm aggregate size fraction was signi?cantly affected by land use and tillage treatments and represented 54%, 43%, and 72%, under NV, CT, and NT in 0–20 cm depth, respectively. Furthermore, the 8–19 mm size fraction stored 55%, 45%, and 71% of the total SOC stock under NV (53.8 Mg C ha-1), CT (28.5 Mg C ha-1) and NT (51.2 Mg C ha-1), respectively. At the LRV site, the 8–19 mm aggregate size fraction decreased from 50% under Cerrado NV to 35% under CT, and ranged from 33% to 51% under diverse biomass-C input under NT in 0–20 cm depth. The 8–19 mm size fraction stored 52%, 37%, and 41% of the total SOC stock across all aggregate sizes under NV (25.4 Mg C ha-1), CT (11.7 Mg C ha-1), and NT (9.9–18.1 Mg C ha-1), respectively. The difference in SOC stock among land uses is largely attributed to storage in the 8–19 mm aggregate size class, indicating that NT cropping systems rebuilt the largest macroaggregates, which are crucial for stabilization of SOC.

Newsletter with papers about CA World Congress : New Delhi Declaration on Conservation Agriculture (CA), paper of K.L. Chadha about CA and horticulture Systems, paper of Rattan Lal about Principles of sustainable soil management

Tropical soils caracteristics, SOC, Demography, Hunger, Food security, soils erosions, biofuels, cereal productions, agricultural intensification, soil management, sustainability.

Programme du séminaire "les sols tropicaux en Semis direct SCV en français et en anglais, avec présentations des sociétés scientifique (IUSS, WASWC, SBCS, AFES) et conférence introductive R. Lal