Effectiveness of 2-Years of Enhanced-Efficiency Fertilizers in Reduction N2o Emissions From Urea Applied to Sugarcane.

The environmental balance of biofuels from sugarcane has been questioned due to greenhouse gases emissions during biomass production, especially nitrous oxide (N₂O) connected to nitrogen fertilization, which can represent 40% of total greenhouse gases emissions in ethanol production. N₂O emissions may be reduced by substitution of conventional fertilizer with enhanced-efficiency fertilizers, but the extent of this benefit is not clear. The objective of this work was to evaluate the effectiveness of nitrification inhibitors (Dicyandiamide (DCD) and 3,4 dimethylpyrazole phosphate (DMPP)) and controlled release fertilizer to reduce N₂O emissions from N fertilizers applied at a rate of 120 kg ha^-1. A sugarcane field experiment was carried out in Campinas, Sao Paulo, Brazil (22º52’15” N, 47º04’57” W) during two ratoon cycles, the first started in April 2012 and finished in November 2012 (217 days) and the second ratoon period is in evaluation yet, but the data showed was from November 2012 to April 2013 (168 days). The treatments were: 1) No N; 2) Urea; 3) Urea+DCD; 4) Urea+DMPP; 5) Polymer and sulfur coated urea. In the second year, the treatments were replicated in the same area, and were included two treatments: UR+DCD and UR+DMPP in a different area. Measurements of N₂O fluxes were performed using static chambers spaced 1 m from each other. The measurements were done three times per week during the first months, and biweekly during the year. The cumulative N₂O-N emissions in the first ratoon cycle (217 days) were 1100 g ha^-1 in the treatment with no N. The emission in the treatment with urea was 2000 g ha^-1 of N, which corresponded to 0.7% of the N applied. Additions of nitrifications inhibitors to urea drastically reduced N₂O emissions which did not differ from those of the plots without N. The treatment with controlled release fertilizer showed N₂O emissions no different from conventional urea. In the second ratoon (168 days – not finished) the results were similar, total N₂O-N emissions were 400 g ha^-1 in the treatment with no N, and 1300 g ha^-1 of N in the treatment with urea, which corresponded to 0.76% of the N applied. Nitrifications inhibitors also had a strong reduction in N₂O and the controlled release fertilizer did not differ from urea. The nitrification inhibitors reduced more than 90% of the total N₂O emissions from urea, mean of the 2-years. These products can be a great option for mitigation of greenhouse gases emissions in biofuels production.