Soil greenhouse gas emissions under enhanced efficiency and urea nitrogen fertilizer from Australian irrigated aerobic rice production

Aerobic rice production offers a promising solution to improve water use efficiency and reduce methane (CH₄) emissions by minimizing water inundation. However, alternate water-saving methods for rice cultivation can lead to “trade-off” emissions of nitrous oxide (N₂O). A field experiment was conducted over one season measuring soil-derived greenhouse gas emissions in irrigated aerobic rice (Oryza sativa L.) under different N fertilizer management at a rate of 220 kg N ha⁻¹, including a nil treatment (“control”); slow release (180 days) polymer-coated urea (“N180”); banded urea applied upfront (“urea”); and three applications of broadcast urea (“urea-split”). The N180 treatment reduced soil N₂O emissions compared with urea (p < 0.001), with mean cumulative N₂O emissions of 4.36 ± 1.07 kg N ha⁻¹ and 27.9 ± 5.70 kg N ha⁻¹, respectively. Soil N₂O fluxes were high, reaching up to 1916 and 2900 µg N m² h⁻¹ after urea application and irrigation/rain events, and were similar to other irrigated crops grown on heavy textured soils. Fertilizer N management had no effect on soil CH₄ emissions, which were negligible across all treatments ranging from 1.28 to 2.75 kg C ha⁻¹ over the growing season. Cumulative soil carbon dioxide emissions ranged from 1936 to 3071 kg C ha⁻¹ and were greatest in N180. This case study provides the first evidence in Australia that enhanced efficiency nitrogen fertilizer can substantially reduce N₂O emissions from soils in an aerobic rice system. Our findings reinforce the CH₄ mitigation potential of water saving rice approaches and demonstrate the need to consider N fertilizer management to control N₂O emissions.