Turning point of direct N2O emissions in China’s croplands dominated by reduced fertilizer usage since 2015

Abstract

Large amounts of nitrogen fertilizers have been applied into China’s croplands to ensure adequate crop production, leading to massive direct nitrous oxide (N₂O) emissions from cropland soils. Since 1980, the agricultural direct N₂O emissions in China have shown sustained and impressive growth, associated with the expansion of croplands and intensified fertilization practices. However, it remains uncertain how direct N₂O emissions have responded to recent agricultural policies characterized by reducing N fertilizer use and adjusting crop mix. This lack of clarity limits practical insights into the effectiveness of these policies. To fill this gap, we here provided a more detailed and timely assessment of crop-specific N₂O emissions during 1980–2022 based on a comprehensive N₂O-emission factor dataset and the random forest algorithm. The resulting estimation exhibited a long-term average of 174.7 Gg N₂O-N yr⁻¹, with 46 % of it contributed by staple crops (rice, maize and wheat) and 44 % from three cash crops (vegetables, fruit and tea). The temporal sequences revealed a noticeable increase over 1980–2015, peaking in 2015 at 259.9 Gg N₂O-N yr⁻¹, followed by a subsequent decline to 215.3 Gg N₂O-N yr⁻¹ by 2022. The divergent trends of N₂O emissions were observed countrywide, with the turning point at 2015 recognized across more than three-quarter croplands. N application was identified as the fundamental driver for this temporal trajectory, especially the decline after 2015. This study affirms the great environmental benefits from the actions targeted at reducing fertilizer usage and enhancing efficiency since 2015. It also provides valuable insights for estimating and mitigating global N₂O emissions from croplands.