Sugarcane residue and N-fertilization effects on soil GHG emissions in south-central, Brazil

Ethanol derived from sugarcane (Saccharum officinarum) could replace a substantial amount of fossil fuel in Brazil, provided the greenhouse gas (GHG) budget is balanced. Green harvest systems have significantly increased the potential amount of sugarcane residue (straw) available for harvest and bioenergy production, but several questions about how those practices will affect field GHG fluxes. In this sense, we quantified GHG emissions associated with four straw harvest rates (12 [no removal]; 6 [moderate removal]; 3 [high removal] and 0 Mg ha(-1) [total removal] of dry matter of straw left on the soil), with and without 100 L ha(-1) vinasse + N fertilizer [80 kg ha(-1) (NH4)2SO(4)]. GHG fluxes were measured for 60 days using static chambers. Our results showed that total straw removal reduced CO2 and N2O emissions by 15% and 25%, respectively. After vinasse and fertilizer additions, CO2 emissions were 2.5-fold higher, and N2O were 5-fold higher, regardless of straw rates. In additional, synergic effect of vinasse + fertilizer and straw removal decreased 60% CH4 uptakes. Direct N2O emission factor was estimated at 0.32%. Net GHG emissions induced by vinasse + fertilizer applied in the sugarcane plantation were 220 g m(-2) CO2e (or 60 g m(- 2) C-equivalent), disregarding straw harvest rate. Therefore, we conclude that maintaining at least 6 Mg ha -1 of sugarcane straw in the field will result in a 'win win situation' by mitigating GHG emissions, sustaining soil, and still saving part of the raw-material for bioenergy production.