The physical protection of soil organic carbon in aggregates: a mechanism of carbon storage in a Vertisol under pasture and market gardening (Martinique, West Indies)

Soil aggregation can influence the storage of carbon in soil. The role of soil structure on soil respiration was investigated by destructive treatment (crushing, dry–wetting events). The soil was a Vertisol under market gardening, a 5-year-old pasture and a long-term pasture. When the soil structure was affected by crushing, soil respiration increase from 1 to 3.4 times. This increase, which represented the amount of protected soil organic carbon (SOC), was much higher in soil under pasture than under market gardening cultivation. There was a positive correlation between the amount of protected SOC and total SOC content. The rate of decay of the protected SOC seemed to be slightly higher than the rate of decay of the unprotected SOC. Because Vertisol is a clayey soil dominated by 2/1 clays, it showed a high capacity to protect mineralisable SOC from mineralisation in macro-aggregates compared with literature results. Even if the protected SOC in aggregates amounted to less than 10% of the total SOC, it represented more than 50% of the mineralisable SOC of a pasture soil. This mechanism seemed then to be an important factor to understand SOC storage in soil under pasture.