Effects of polymer- and nitrification inhibitor-coated urea on N2O emission, productivity and profitability in a wet tropical sugarcane crop in Australia

Weijin Wang1,2, Lawrence Di Bella3, Steven Reeves1, Melissa Royle3, Marijke Heenan1, Minka Ibanez3

1 Department of Science, Information Technology and Innovation, 41 Boggo Road, Dutton Park QLD 4102, Australia; Email: [email protected]

2 Environmental Futures Research Institute, Griffith University, Nathan, QLD 4111, Australia

3 Herbert Cane Productivity Services Limited, 181 Fairford Rd, Ingham, QLD 4850, Australia

Abstract

Sugarcane crops are predominantly grown in warm and high rainfall or irrigated areas where substantial fertiliser nitrogen (N) losses can occur. This study was conducted in a wet tropical sugarcane cropping system to assess polymer-coated urea (PCU), polymer- and sulphur-coated urea (PSCU) and the denitrification inhibitor DMPP-coated urea (NICU) on sugar productivity, N use efficiency and profitability at the normal application rate (150 kg N/ha) and a reduced rate (110 kg N/ha). Nitrous oxide (N2O) emissions were also measured for selected treatments using automatic and manual gas sampling chambers in combination. The results demonstrated that annual cumulative N2O emissions in the treatment receiving conventional urea at 150 kg N/ha amounted to 4.74 and 9.51 kg N2O-N/ha, with the fertiliser N emission factor of 1.90 and 3.01%, based on the manual and automatic chamber measurements, respectively. Application of NICU decreased the annual fertiliser-induced N2O emission by approximately 83%. However, N2O emissions in the PSCU treatment were about two times that in the conventional urea treatment, probably due to less N leaching from PSCU. Use of PCU, PSCU and NICU at 150 kg N/ha increased the sugar yield by 2.5, 3.3 and 2.8 t/ha, respectively, compared to the conventional urea treatment (8.4 t/ha). The crop N uptake in the aboveground biomass were significantly higher for the coated urea fertilisers than uncoated urea, and higher for PSCU and NICU than PCU at 150 kg N/ha. The farming profits also tended to be higher for the coated urea fertilisers than the conventional urea.