Nitrogen fertilizer consumption and nitrous oxide emissions associated with ethanol production – A national-scale comparison between Brazilian sugarcane and corn in the United States

Globally, Brazil and United States (US) have the large-scale programs of biofuels production. Among other parameters, the feasibility and sustainability of petroleum-based fuels by biofuels replacement depend upon the proper nitrogen (N) fertilizers usage as well as the associated nitrous oxide (N₂O) emissions along the production chain. The efficiency of N use also depends on the choice of biofuel crop. Previous studies indicated that sugarcane (Saccharum spp.) requires less N than corn (Zea mays L), thus, the hypothesis tested was that Brazilian sugarcane-based ethanol requires less synthetic N inputs per unit produced than corn-based ethanol in the US. Consequently, ethanol production in Brazil from sugarcane has lower N₂O emissions associated with N fertilization than ethanol produced in the US from corn. Here, we reviewed national-scale dataset on sugarcane and corn cultivation in Brazil and US respectively, in order to compare temporal changes in the cultivated area for both crops (devoted for ethanol production), N-fertilizers consumption, and associated emission of N₂O in the period 2000–2020. The same parameters were forecasted for the upcoming decade. For both periods, there were calculated two indexes: the N-fertilizer consumption index (the quotient of N-fertilizer input by ethanol production) and the N₂O emission index (the quotient of N-fertilizer input by N₂O emission). In the period 2000–2020, the devoted area for sugarcane and corn cultivation increased around 43 and 9%, respectively, while the N rates recorded in 2020 for sugarcane in Brazil and corn in the US averaged, respectively, 78 and 167 kg ha⁻¹ N. Moreover, within the 2000–2020 period, the average yield was 74 Mg ha⁻¹ for sugarcane (stalks) in Brazil and 9.6 Mg ha⁻¹ for corn (grain) in the US, which resulted in ethanol yield (in area basis) of 6009 and 4003 L ha⁻¹, respectively. Thus, the N-fertilizer consumption index was much lower for sugarcane-based ethanol than for corn-based ethanol (0.009 versus 0.04 kg N L⁻¹). Through the Intergovernmental Panel on Climate Change (IPCC) emission factor (Tier 1), we estimated that N₂O emission is 4.6 times lower for sugarcane-based ethanol than for corn-based ethanol (94 versus 433 mg N₂O per L⁻¹). By 2030, ethanol production might reach 45 and 58 billion L in Brazil and within the US, respectively, leading to 0.45 and 2.07 million t of N-fertilizer consumption per year⁻¹ for sugarcane and corn respectively. The outcomes herein endorse the sustainability of sugarcane as a feedstock for ethanol production and may guide stakeholders to establish public policies to enable sugarcane-based ethanol production as one alternative to tackle global warming and climate changes.