Organic carbon within soil aggregates under forestry systems and pasture in a southeast region of Brazil

Abstract The location of organic matter within the aggregate is a key factor for stabilizing and storing soil organic carbon (SOC). In this context, the purpose of this study was to answer the following question: How much is the contribution of aggregate associated-C in total SOC accumulation up to 1 m under different land uses in the Atlantic rainforest zone of Brazil? The experimental areas were: a secondary-forest; 3 and 5-year-old eucalyptus plantation; 35-year-old rubber tree plantation; and 50-year-old unfertilized pasture. Soil samples were collected at six different depths (0–10, 10–20, 20–40, 40–60, 60–80 and 80–100 cm), air dried and separated by wet-sieving into three fraction-size classes (2000–250 μm; 250–53 μm and Ma ) than microaggregates (C Mi ). The amount of C Ma stock in all land-use systems ranged from 33 to 8 Mg ha −1 , and the C Mi ranged from 11 to 7 Mg ha −1 . This represents around 22 to 4% and 7 to 4%, respectively, of physically protected C in the SOC storage up to 100 cm. The amount of C Ma  + C Mi up to 1 m was 43 Mg ha −1 and 36 Mg ha −1 under 3- and 5-year-old eucalyptus plantations; 30 Mg ha −1 in the in secondary forest; and 19 Mg ha −1 in the rubber plantation and pasture. The C stabilization within aggregates represents a significant mechanism of C protection in these soils.