Long-term and excessive nitrogen (N) fertilization generally exerts negative impacts on soil biodiversity, particularly for soil organisms with larger body sizes. Organic amendments such as straw return are widely recommended to mitigate such declines. However, most studies have focused on taxonomic responses, and empirical evidence remains scarce regarding how these practices shape energy fluxes within soil animal food webs, especially those of soil macrofauna. Using a manipulative study nested within a 22-year field experiment on the Chinese Loess Plateau, we examined the independent and interactive effects of N fertilization (0, 120, 240 kg ha(-1) yr(-1)) and straw incorporation (0, 7500 kg ha(-1) yr(-1)) on total soil macrofauna energy flux, and energy fluxes across distinct feeding guilds (i.e., decomposers, root herbivores, omnivores, and predators). We found that N fertilization and straw incorporation alone increased total macrofauna energy flux by 62.9% and 143.3%, respectively, via distinct pathways: N fertilization enhanced mean body size (trait-driven), whereas straw incorporation boosted abundance (density-driven). Under straw incorporation, N fertilization shifted the macrofauna response, particularly in omnivores, from increased abundance toward larger body size, suggesting an allometric trade-off between community expansion and individual growth. Despite these pronounced changes in community structure, no significant interaction between the two practices was detected for total energy flux. Strikingly, decomposers (dominated by earthworms) contributed over 90% of total flux, decoupling classical biodiversity-ecosystem functioning relationships. These findings show that N fertilization and straw returning boost soil macrofauna energy flux via distinct trait- vs. density-driven pathways, and highlight the importance of conserving keystone taxa alongside broader biodiversity in sustainable agricultural management.