Soil carbon changes in areas undergoing expansion of sugarcane into pastures in south-central Brazil

In Brazil, sugarcane expansion for ethanol production has been predominantly on areas previously used as pasture. Losses of C and N induced by land use change raise controversies about the environmental suitability of biofuel production. Therefore, we conducted a field study within the largest sugarcane-producing region of Brazil to evaluate the effects of the primary land use change (LUC) sequence in sugarcane expansion areas (i.e., native vegetation to pasture to sugarcane), on C and N dynamics in the top 1 m soil layer. The LUC sequences caused substantial but varying changes in soil C and N stocks in areas undergoing expansion of sugarcane in south-central Brazil. The increase of C stocks in areas converted from pasture to sugarcane cultivation was 1.97 Mg ha−1 yr−1, in contrast to conversion of native vegetation to pasture, which decreased soil C stocks by 1.01 Mg ha−1 yr−1 for 0-1.0 m soil layer. The use of 13C measurements to partition soil C sources showed that the greater C stocks in sugarcane areas compared to pasture was due to retention of the native-C stocks and increased accrual of modern-C comparing to pasture. Finally, the inclusion of deeper soil layers, at least down to 1.0 m depth, is essential to assess the impacts of LUC on C balances in agricultural areas.