Purpose <p>The biochemical composition of crop straw plays a crucial role in governing net nitrogen (N) immobilization or mineralization. However, few studies have comprehensively explored the effects of straw return practices (incorporation vs. mulch) on field-scale N loss from the perspective of straw biochemical composition.</p> Methods <p>Here, we combine comprehensive databases for field reactive N loss from straw return practices and crop straw biochemical characteristics with a mixed-effects meta-regression model selection, to investigate the effects of straw incorporation and mulch on global reactive N losses, including nitrous oxide (N₂O) emissions, ammonia (NH₃) volatilization, and N leaching.</p> Results <p>For different straw return methods, N₂O emissions increased by 35.2% under straw mulch and 20.2% under straw incorporation. While straw mulch significantly reduced N leaching by 27.4%, straw incorporation showed no significant effect. Variations in N₂O and NH₃ emissions were best explained by readily degradable carbon fractions, particularly water-soluble carbon. In addition, straw with a C: N ratio &lt; 20 increased NH₃ volatilization.</p> Conclusion <p>Our findings provide valuable insights to promote sustainable straw return practices globally.</p>