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During the past few decades, commercial silvopastoral systems (SPS) with exotic Eucalyptus (hybrid) trees have become popular in the Brazilian Cerrado (savanna). With the increasing awareness about the role of carbon (C) storage in soils as a climate-change mitigation strategy and the relationship between the nature of soil aggregates and the soil's carbon sequestration potential, it is important to understand the influence of such SPS systems on soil organic carbon (SOC) storage. We studied C content in three aggregate size classes in six land-use systems on Oxisols in Minas Gerais, Brazil. The systems were planted forest, native secondary forest, managed pasture, and three 8-year-old SPS, differing in their tree-planting configurations. Eucalyptus hybrid was the tree in SPS and planted forest treatments, and Urochloa decumbens was the grass in SPS and pasture treatments. From each treatment, replicated soil samples were collected from four depth-classes (0–10, 10–30, 30–60, and 60–100 cm), fractionated by wet sieving into the three aggregate-size classes, 2000 to 250 μm, 250 to 53 μm, and <53 μm size classes representing macroaggregates, microaggregates, and silt + clay, respectively, and their C contents determined. Down to 1 m, total SOC stock values ranged from 260 Mg ha−1 under pasture to 167 Mg ha−1 under native forest, with 174 Mg ha−1 for Eucalyptus plantation and about 195 Mg ha−1 for the three SPS. Compared to the degraded native forest, the pasture system had significantly higher SOC in the whole soil and the aggregate size fractions, especially in the lower soil-depth classes. The lower SOC stock of Eucalyptus hybrid SPS compared to open pasture differs from the general trend of SPS having higher stock. Given that the Cerrado biome is a biodiversity hotspot, the use of native nitrogen-fixing trees, of which there are several, is worth investigating. In addition, the conversion from Eucalyptus monocultures to SPS could be considered as a strategy to increase the SOC stock. • Soil C stock up to 1 m depth was significantly higher under pasture (260 Mg ha−1). • Pasture differed from other treatments in terms of soil C stock in deeper profiles. • Eucalyptus silvopastures had an intermediate level of soil C stock (∼195 Mg ha−1). • Macroaggregates stored most of the soil C stock, more so in the pasture treatment. [ABSTRACT FROM AUTHOR]

Biofuels are predicted to constitute a large proportion of fuel consumption in the global transport sector under stringent climate mitigation polices in future. In Brazil, sugarcane ethanol has been widely deployed at large scale and an oriented expansion of sugarcane is considered to be a key measure to ensure the expected positive outcomes from biofuels. In this study, more recent and accurate georeferenced information were combined with an enhanced land use classification system to update the original Sugarcane Agroecological Zoning (SAEZ). We also excluded environmentally relevant areas (ERA) in our updated SAEZ to create a new set of reference maps for supporting future prioritization of areas for sugarcane ethanol expansion. We mapped 41.7 Mha as suitable land for sugarcane expansion in center-south region of Brazil, differently from the 50 Mha indicated in the original SAEZ. After excluding the ERA, 33.7 Mha was found to be suitable for sugarcane expansion, of which 20 Mha is currently occupied with pasture lands. About half of these areas were located in Mato Grosso do Sul and Minas Gerais states and an exploratory assessment of two microregions from these states demonstrated the importance of conducting regional assessments to prioritize the areas for a more sustainable sugarcane expansion to meet future bioenergy demands. • Our analysis identified an area 17% smaller than original agro-ecological zoning suitable for sugarcane expansion. • By excluding environmentally relevant areas, the total suitable area for sugarcane expansion is reduced to 33.7 Mha. • About two thirds of that area is currently occupied with pasture lands. • About half of suitable areas occupied with pasture lands are in two Brazilian states. • Local conditions are fundamental for oriented expansion of bioenergy production. [ABSTRACT FROM AUTHOR]