Direct N2O emission factors for synthetic N-fertilizer and organic residues applied on sugarcane for bioethanol production in Central-Southern Brazil

The production and use of biofuels have increased rapidly in recent decades. Bioethanol derived from sugarcane has become a promising alternative to fossil fuel for use in automotive vehicles. The savings' calculated from the carbon footprint of this energy source still generates many questions related to nitrous oxide (N2O) emissions from sugarcane cultivation. We quantified N2O emissions from soil covered with different amounts of sugarcane straw and determined the direct N2O emission factors of nitrogen fertilizers (applied at the planting furrows and in the topdressing) and the by-products of sugarcane processing (filter cake and vinasse) applied to sugarcane fields. The results showed that the presence of different amounts of sugarcane straw did not change N2O emissions relative to bare soil (control). N-fertilizer increased N2O emissions from the soil, especially when urea was used, both at the planting furrow (plant cane) and during the regrowth process (ratoon cane) in relation to ammonium nitrate. The emission factor for N-fertilizer was 0.46 +/- 0.33%. The field application of filter cake and vinasse favored N2O emissions from the soil, the emission factor for vinasse was 0.65 +/- 0.29%, while filter cake had a lower emission factor of 0.13 +/- 0.04%. The experimentally obtained N2O emission factors associated with sugarcane cultivation, specific to the major sugarcane production region of the Brazil, were lower than those considered by the IPCC. Thus, the results of this study should contribute to bioethanol carbon footprint calculations. (AU)