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

Abstract Aerobic rice production offers a promising solution to improve water use efficiency and reduce methane (CH 4 ) emissions by minimizing water inundation. However, alternate water‐saving methods for rice cultivation can lead to “trade‐off” emissions of nitrous oxide (N 2 O). 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 N 2 O emissions compared with urea ( p < 0.001), with mean cumulative N 2 O emissions of 4.36 ± 1.07 kg N ha −1 and 27.9 ± 5.70 kg N ha −1 , respectively. Soil N 2 O fluxes were high, reaching up to 1916 and 2900 µg N m 2 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 CH 4 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 N 2 O emissions from soils in an aerobic rice system. Our findings reinforce the CH 4 mitigation potential of water saving rice approaches and demonstrate the need to consider N fertilizer management to control N 2 O emissions.