Nitrogen sources and application rates affect emissions of N2O and NH3 in sugarcane

Best management practices for N fertilization should increase yields while reducing negative environmental effects such as losses by ammonia (NH3) volatilization and emission of greenhouse gases, especially nitrous oxide (N2O). We studied the impact on sugarcane of two N sources (UR: urea and CAN: calcium ammonium nitrate) in three N rates (30, 60, and 90 kg N ha−1 in the plant cane cycle and 60, 120, and 180 kg N ha−1 in ratoons) on a sugarcane field grown on a Red Latosol soil in southeastern Brazil. We measured sugarcane yields and N2O, CO2 and CH4 emissions in three crop cycles (plant cane, 2nd and 3rd ratoons), and NH3 in two crop cycles (2nd and 3rd ratoons). The accumulated emission of N2O from UR was significantly higher in comparison with those of CAN in all three crop cycles. The average emission factors for UR were 0.8% (plant cane), 1.1% (2nd ratoon) and 0.8% (3rd ratoon) and the corresponding figures for CAN were 0.4%, 0.7% and 0.5%, respectively. The N2O intensity was higher for UR (20.3 mg N–N2O kg−1 sugarcane stalk) than CAN (16.2 mg N–N2O kg−1 sugarcane stalk). The NH3 volatilization losses for CAN were less than 1% compared to 5–16% of the N applied as UR. Stalk yield increased with N application, but no difference was observed between UR and CAN. We concluded that CAN has the potential to reduce both NH3 and N2O losses compared with urea and is the preferred N source for sugarcane.