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ABSTRACT The “campos” of the Pampa are unique Brazilian ecosystems, which provide key environmental services, including C storage. These grassy ecosystems have been rapidly converted to intensive land-uses, mainly intensive grain crops (soybeans) and Eucalyptus silviculture. These new land-uses could decrease soil C stocks, depending on soil management. This study aimed to assess soil organic carbon (SOC) changes after the conversion of native grasslands to cropland (soybeans/cover crops under no-tillage) and forestry (Eucalyptus). Eight representative sites in this biome were selected for soil sampling (Alegrete-ALE, Aceguá-ACE, Jari-JAR, Jaguarão-JAG, Pinheiro Machado-PIM, Lavras-LAV, Santo Antônio das Missões-SAM, São Gabriel-SAG). Soil sampling was conducted in dug pits (0.30 m wide × 0.30 m long × 0.40 m depth) spaced by 50 m at each site, to 0.30 m depth. Soil bulk density and SOC were obtained by samples obtained with volumetric rings. Soil organic C was analyzed by dry combustion. Soil C stocks were calculated per layer and cumulatively (0.00-0.20 and 0.00-0.30 m). Soil C content was higher under grasslands in soils from sites with finer, clayey texture (ACE, JAG), and lower in soils at sites with sandier topsoil. Land-use conversion to silviculture and cropland minimally affected SOC stocks. The same pattern was observed with soil N, because of the tight connection between C and N cycles. Soil bulk density was similar across sites and layers, but higher values were measured in sites with coarser texture. Mean SOC stock of the grassland sites was 62 ± 24.6 Mg ha-1, similar to 66 Mg ha-1 reported for grasslands soils of Rio Grande do Sul State, and higher than that reported by IPCC for this region (55 ± 4.4 Mg ha-1). Adopting these default values would lead to underestimation of baseline SOC stocks in the region. Land-use conversion to cropland did not affect SOC stocks significantly, probably because of the adoption of no-tillage system with winter cover crops. Soil C stocks were lower in Eucalyptus stands in the 0.00-0.30 m soil layer, which could be attributed to intensive soil management at planting and lower soil fertility in some sites. This lack of effect of conversion on soil C was attributed to the short time since conversion and adoption of soil conservation practices (no-tillage) in cropland. The study contributed to reduce existing soil data gaps in the region and supports Brazilian public initiatives like the ABC Program and National Greenhouse Gas Inventories. campos “campos services storage landuses, landuses land uses, uses soybeans (soybeans (SOC soybeans/cover soybeanscover notillage no tillage Eucalyptus. . (Eucalyptus) AlegreteALE, AlegreteALE Alegrete ALE, ALE (Alegrete-ALE AceguáACE, AceguáACE Aceguá ACE, ACE Aceguá-ACE JariJAR, JariJAR Jari JAR, JAR Jari-JAR JaguarãoJAG, JaguarãoJAG Jaguarão JAG, JAG Jaguarão-JAG MachadoPIM, MachadoPIM Machado PIM, PIM Machado-PIM LavrasLAV, LavrasLAV Lavras LAV, LAV Lavras-LAV MissõesSAM, MissõesSAM Missões SAM, SAM Missões-SAM GabrielSAG. GabrielSAG Gabriel SAG Gabriel-SAG) 030 0 30 (0.3 0.3 040 40 0.4 depth 5 site rings combustion 0.000.20 000020 0.00 0.20 00 20 (0.00-0.2 0.000.30 000030 0.00-0.3 m. m) finer (ACE , JAG) topsoil Landuse Land use cycles layers 6 246 24 24. ha1, ha1 ha 1, 1 ha- State 55 (5 44 4 4. ha1. ha-1) significantly (no-tillage Inventories (Eucalyptus Gabriel-SAG 03 3 (0. 0. 04 000 0.000.2 00002 0.0 020 0.2 2 (0.00-0. 0.000.3 00003 0.00-0. ( (0 0.000. 0000 02 (0.00-0 0.00-0 0.000 (0.00- 0.00- (0.00 (0.0