Central Role of Nitrogen Fertilizer Relative to Water Management in Determining Direct Nitrous Oxide Emissions From Global Rice-Based Ecosystems

Abstract

The increasing atmospheric nitrous oxide (N₂O) concentration stems from the development of agriculture. However, N₂O emissions from global rice-based ecosystems have not been explicitly and systematically quantified. Therefore, this study aims to estimate the spatiotemporal magnitudes of the N₂O emissions from global rice-based ecosystems and determine different contribution factors by improving a process-based biogeochemical model, TRIPLEX-GHG v2.0. Model validation suggested that the modeled N₂O agreed well with field observations under varying management practices at daily, seasonal, and annual steps. Simulated N₂O emissions from global rice-based ecosystems exhibited significant increasing trends from 0.026 ± 0.0013 to 0.18 ± 0.003 TgN yr⁻¹ from 1910 to 2020, with ∼69.5% emissions attributed to the rice-growing seasons. Irrigated rice ecosystems accounted for a majority of global rice N₂O emissions (∼76.9%) because of their higher N₂O emission rates than rainfed systems. Regarding spatial analysis, Southern China, Northeast India, and Southeast Asia are hotspots for rice-based N₂O emissions. Experimental scenarios revealed that N fertilizer is the largest global rice-N₂O source, especially since the 1960s (0.047 ± 0.010 TgN yr⁻¹, 35.24%), while the impact of expanded irrigation plays a minor role. Overall, this study provides a better understanding of the rice-based ecosystem in the global agricultural N₂O budget; further, it quantitively demonstrated the central role of N fertilizer in rice-based N₂O emissions by including rice crop calendars, covering non-rice growing seasons, and differentiating the effects of various water regimes and input N forms. Our findings emphasize the significance of co-management of N fertilizer and water regimes in reducing the net climate impact of global rice cultivation.