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The early natural forest conversion to pasture, rubber tree plantations or agroforestry systems (AFSs) will not negatively affect soil organic carbon (SOC) accumulation due to the lack of soil tillage and the continuous contribution of vegetal residues to the soil, over the years, which would favor C occlusion in soil aggregates. The objectives of this study were: to evaluate the potential of AFSs with rubber trees to accumulate SOC up to 100 cm; to evaluate the δ 13 C variations over the soil profile after forest to pasture and rubber tree plantation (RTP) conversion; and to verify the C physical protection in aggregates as a mechanism of C stability in these soils. SOC was quantified up to 100 cm in whole soil and in three fraction-size classes (macroaggregates, microaggregates and silt + clay class). The occluded C was quantified in macroand microaggregates by using an ultrasonic method. The relative contributions of C 3 and C 4 plants-derived C were quantified. The RTP system presented the highest SOC values, up to 100 cm depth, contributing with 20 Mg C ha −1 from belowground input, during 35-year old of system implantation. However, about 90% of SOC was not physically protected in the soil aggregates. The forest to rubber + cacao agroforestry system (AFS) conversion reduced SOC stock up to 100 cm approximately 72 Mg ha −1 , and the reduction in SOC stock after forest to rubber tree + açaí AFS was around 34 Mg ha −1. Rubber tree + cacao and rubber tree + açaí AFSs had significant contributions of occluded C in soil aggregates.

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Brazil is one of the main producers in the agricultural and forestry sector worldwide, with production systems based on high consumption of inputs that contribute to high levels of greenhouse gas (GHG) emissions. This paper presents an analysis of the scenario of national GHG emissions and carbon footprints in the major production systems of agriculture, including livestock production and forestry, and the potential for soil carbon storage as a mitigation strategy under these systems. The main sources of national GHG emissions are beef cattle due to enteric fermentation and the management of agricultural soils through the use of nitrogen fertilizers. The increasing adoption of low-carbon agriculture has led to a reduction in the carbon footprint through no-till technologies, agrosilvopastoral systems, N2 fixation, and tree plantations. These technologies deserve to be increasingly disseminated to generate economic opportunities leading to financial gains from the commercialization of carbon credits and payment for environmental services.