Losses and gains of soil organic carbon in grasslands in the Brazilian semi-arid region

Studies show that soil organic carbon (SOC) decreases between 3 % and 9 % in degraded grasslands in tropical regions, mainly due to the absence of techniques to enhance carbon contribution to soils. This study assessed SOC stock change factors for grassland management, specific to the semi-arid region of Brazil. These factors may contribute to a better understanding of SOC dynamics and could be used to improve inventories on GHG emissions. In addition, they could be used for updating default factors used by the Intergovernmental Panel on Climate Change. This study considers both soil sampling and a literature review, and comprises 27 paired comparisons, where the dataset was analyzed using a mixed linear model. For the grassland in the Brazilian semi-arid region, the SOC stock is reduced by between 12 % and 27 % due to inadequate management, overgrazing, and edaphoclimatic conditions of the Brazilian semiarid. However, this depends on aspects, such as land use and soil layer, which represents substantially more severe losses than in other regions of the country. We also found that losses occur during the first five years after conversion of native vegetation. The results also indicated a trend for SOC stocks to recover over time, reaching 4 % after 30 years of use as grassland, probably related to the long period without soil tillage and the role of gramineas root system.