Quantifying above and belowground biomass carbon inputs for sugar-cane production in Brazil

Expansion of sugarcane crop due to the increasing demand for sugar and ethanol can affect both existing soil carbon (C) stocks, and subsequent input of new C from above and belowground biomass, influencing the overall C intensity and C payback times due to the change of land use. We present above and belowground dry biomass production, shoot-to-root ratio (S:R) as well as the net annual C inputs to the soil for sugarcane in different ratoon stages. The selected areas were as follows: (1) recently planted sugarcane area (PC), (2) first year ratoon cane (RC1) and (3) 4-year ratoon cane (RC4), which were established under Typic Quartzipsamments located in north-eastern Sao Paulo State. The sugarcane S:R ratios ranged from 6.6 in PC to 3.4 in RC4, and total sugarcane C inputs from 29.6 to 30.8 Mg C ha–1. The overall C balance for land use change requires effects on soil C and also C inputs from previous and future land uses. The sugarcane C input was between 3.7 and 4.0 Mg C ha–1 for each sugarcane cycle of 5 years. When accounting for soil C stock changes and aboveground biomass C losses from the prior land use, the payback times for sugarcane biofuel C debts are reduced by 3, 2 and 1 years for Cerrado wooded, Cerrado grassland and pasture conversions into sugarcane respectively.