Crop residue removal and nitrification inhibitor application as strategies to mitigate N2O emissions in sugarcane fields

Nitrous oxide (N2O) emission estimates are important to ascertain the greenhouse gas balance of ethanol produced from sugarcane. We quantified N2O emissions in the presence of sugarcane crop residues, N fertilizer (ammonium sulfate), and a nitrification inhibitor (NI, dicyandiamide). Two field experiments were conducted to evaluate the implications of N fertilizer application during dry and wet seasons at two locations in southeast Brazil. Treatments consisted of four levels of crop residue (0, 5, 10, and 15 Mg ha(-1)) and three of N fertilizer (0 and 120 kg ha(-1) and 120 kg ha(-1) plus NI). N2O emission was measured using the closed chamber method and sugarcane yield via mechanical harvest. N2O emissions were higher in wet than in dry seasons following N fertilizer application, albeit affected by crop residue and NI in both. Retaining crop residues on the soil increased N2O emission and sugarcane yield. The N2O emission factor from N fertilizer ranged from 0.12% to 1.44% of N applied. NI reduced N2O emissions (by 87% and 63% in dry and wet seasons, respectively). Sugarcane yield varied from 42 to 92 Mg ha(-1) of fresh matter stalk and emission intensity from 3.7 to 22.9 kg of CO2eq, Mg of stalk(-1). The lowest greenhouse gas intensity was recorded with 5 Mg ha(-1) crop residue and 120 kg ha(-1) N supplemented with NI. Therefore, partial crop residue removal and NI addition to N fertilizer may be effective strategies to improve the sustainability index of biofuel from sugarcane and reduce N2O emissions and intensity. (AU)