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.

Four points to convince the farmers to adopt the DMC systems (SCV) in large scale : - Reduction of costs - Reduction of the risks with weather impact (drought) - Increase the yield of the main cash crop and the profitability of the whole system - Making extra money with C-sequestration and giving a good contribution to the environment.

Diaporama sur MO dans le sol (partie 1)

Diaporama sur MO dans le sol (partie 2 = restauration MO par système de culture en Semis Direct)

The aggregation in no-tillage soils is built on the horizontal layers and the temporary and transient biding agents are the most important aggregation components

The carbon cycle in soil with soils biology, organic chemistry,

Définition de l'agriculture de conservation et des SCV en anglais.

Ces résultats expérimentaux et ces observations en vraie grandeur montrent que le système SCV, soit le semis direct sans travail de perturbation du sol associé à la rotation de cultures combinées avec des plantes de couverture produisant en permanence de la phytomasse conduit le sol cultivé à fonctionner en mode puits (drainage) plutôt qu’en mode source ( émission) de CO2. Au niveau global, ce service rendu à l’environnement ne pourra à terme être ignoré. A l’échelle locale, la protection de la MOS à l’intérieur de néo-agrégats constitue la composante clé générique de la résilience des systèmes SCV. Pour l’agriculteur de demain au Brésil, la gestion de la Matière Organique du Sol peut raisonnablement être considérée comme la base d’une stratégie gagnante qu’autorisent ces modes de gestion des cultures dans la mesure ou il a été démontré à grande échelle qu’ils assurent par ailleurs la viabilité et la durabilité de l’exploitation agricole.

Principes et clés pour l'action. Restitution de la formation UEPG/Cirad au Brésil par le collectif SCV.

Diaporama upon 2 cases in Brasil (1 in cerrados, 1 in Parana subtropical): Evolution of the O.M. in quantity & quality with differents systems (DMC and till conventional)