Refining the Factors Affecting N2O Emissions from Upland Soils with and without Nitrogen Fertilizer Application at a Global Scale

Abstract

Nitrous oxide (N₂O) is a long-lived greenhouse gas that mainly originates from agricultural soils. More and more studies have explored the sources, influencing factors and effective mitigation measures of N₂O in recent decades. However, the hierarchy of factors influencing N₂O emissions from agricultural soils at the global scale remains unclear. In this study, we carry out correlation and structural equation modeling analysis on a global N₂O emission dataset to explore the hierarchy of influencing factors affecting N₂O emissions from the nitrogen (N) and non-N fertilized upland farming systems, in terms of climatic factors, soil properties, and agricultural practices. Our results show that the average N₂O emission intensity in the N fertilized soils (17.83 g N ha⁻¹ d⁻¹) was significantly greater than that in the non-N fertilized soils (5.34 g N ha⁻¹ d⁻¹) (p< 0.001). Climate factors and agricultural practices are the most important influencing factors on N₂O emission in non-N and N fertilized upland soils, respectively. For different climatic zones, without fertilizer, the primary influence factors on soil N₂O emissions are soil physical properties in subtropical monsoon zone, whereas climatic factors are key in the temperate zones. With fertilizer, the primary influence factors for subtropical monsoon and temperate continental zones are soil physical properties, while agricultural measures are the main factors in the temperate monsoon zone. Deploying enhanced agricultural practices, such as reduced N fertilizer rate combined with the addition of nitrification and urease inhibitors can potentially mitigate N₂O emissions by more than 60% in upland farming systems.