Effect of long-term and soil depth on soil organic carbon stocks after conversion from native vegetation to conventional tillage systems in Brazil

Deforestation of native vegetation (NV) for the expansion of agriculture under conventional tillage (CT) is still an important land-use change in Brazil. Therefore, we quantified the impact of this land-use change on the soil organic carbon (SOC) stocks in different Brazilian biomes, by deriving SOC stock-change factors covering different periods and soil layers. In the present research, 37 studies were used, with a total of 111 paired comparisons distributed over the different Brazilian biomes, and analyzed the data in linear mixed-effect models. In Brazil, converting NV to CT results in a progressive reduction (1%−26%) in SOC stocks over time, affecting both the surface and deeper layers. However, these impacts occur differently between the Brazilian biomes, since in the Cerrado biome, losses are less intense than the national average, especially those seen the Caatinga and Atlantic Forest. Furthermore, there were no signs of SOC losses stabilising before 40 years of land use both in the Caatinga or the average data for Brazil, nor before 30 years in the Cerrado, indicating that soils under CT continue to lose SOC even after the standard period 20 years adopted by the IPCC.