Bioethanol production from sugarcane and emissions of greenhouse gases - known and unknowns

Bioethanol production from sugarcane is discussed as an alternative energy source to reduce dependencies of regional economies on fossil fuels. Even though bioethanol production from sugarcane is considered to be a beneficial and cost-effective greenhouse gas (GHG) mitigation strategy, it is still a matter of controversy due to insufficient information on the total GHG balance of this system. Aside from the necessity to account for the impact of land use change (LUC), soil N2O emissions during sugarcane production and emissions of GHG due to preharvest burning may significantly impact the GHG balance. Based on a thorough literature review, we show that direct N2O emissions from sugarcane fields due to nitrogen (N) fertilization result in an emission factor of 3.87 +/- 1.16% which is much higher than suggested by IPCC (1%). N2O emissions from N fertilization accounted for 40% of the total GHG emissions from ethanol-sugarcane production, with an additional 17% from trash burning. If LUC-related GHG emissions are considered, the total GHG balance turns negative mainly due to vegetation carbon losses. Our study also shows that major gaps in knowledge still exist about GHG sources related to agricultural management during sugarcane production, e. g. effects of irrigation, vinasse and filter cake application. Therefore, more studies are needed to assess if bioethanol from sugarcane is a viable option to reduce energy-related GHG emissions.