Potential for carbon sequestration in soil under forest and pasture with different times and levels of intensification in the Eastern Amazon

The conversion of forests into grazing systems impacts carbon (C) sequestration in Amazonian soils. The objective of the study was to quantify the C and soil sequestration potential under a forest system that has been fallow for 30 years, intensive pasture with Urochloa humidicola, one system with a 10-year history of intensification and another intensified through soil correction for 3.5 years. The study was conducted in the municipality of São Miguel do Guamá-Pará, with one collection in 2021 and another in 2025. The soils were classified as Yellow Latosols, with a sandy loam texture. The data were submitted to analysis of variance and the means were compared using the Student-Newman-Keuls test (P<0.05). C stocks in the 0–30 cm layer were significantly higher in intensified pasture (43.79 Mg ha⁻¹) compared to forest (33.85 Mg ha⁻¹) (P<0.05), while recently intensified pasture showed intermediate values (40.47 Mg ha⁻¹). In the 0–100 cm layer, intensified pasture maintained higher stocks, ranging from 72.4 to 88.64 Mg ha⁻¹ with no differences (p > 0.05). The variation factor for soil organic carbon in relation to the same treatment was 1.61 and 1.06 for the forest, 1.22 and 1.01 for intensified pasture, and 1.34 and 1.08 for recently intensified pasture in the 30 and 100 cm layers. The results show that all systems act as carbon sinks, with sustainable pasture intensification contributing to increased soil carbon stocks and that the forest, even after 30 years of fallow, is not yet stabilized.