Anthropogenic nitrogen (N) input has overtaken natural N fixation as the largest reactive N source and is predicted to stimulate ecosystem carbon (C) sequestration. Most studies of N effects on soil C balance have focused on biological processes that control C input (plant production) and C output (microbial decomposition), but few have examined the general patterns of N effects on the physiochemical processes that regulate soil organic C persistence. We synthesized results from 87 publications that examined effects of experimental N input on soil aggregation, a key process controlling soil C persistence, and its related processes. Globally, N input significantly enhanced plant shoot and root biomass, and the formation of soil macroaggregates and their size (measured as mean weight diameter, MWD; P < 0.05). Surprisingly, N-enhancement of root biomass and soil aggregation primarily stemmed from urea applications. Although urea input reduced microaggregates, it increased macroaggregates (+6.9%) and MWD, likely due to enmeshment by urea-induced root growth (+20.5%). In contrast, other forms of N input (combined NH₄⁺, NO₃⁻ and NH₄NO₃) did not significantly affect root biomass, microaggregates or macroaggregates, but reduced microbial biomass C. Further, N-promotion of soil aggregation occurred mainly in croplands under low to moderate N input (<200 kg N ha⁻¹ yr⁻¹). Together, these results indicate that the form of N fertilizer exerts a primary control over N effects on plants, microbes, and soil aggregation. Our findings suggest that combination of urea fertilizers and reduced perturbations (e.g., reduced-tillage) may be key to enhance soil aggregation and organic C retention and persistence in vast agroecosystems.

人为氮（N）的输入已超过自然固氮，成为最大的反应性氮源，预计会刺激生态系统碳（C）的固存。氮对土壤碳平衡的影响的大多数研究都集中在控制碳输入（植物生产）和碳输出（微生物​​分解）的生物过程上，但很少研究过氮对调节土壤有机碳持久性的理化过程的一般模式。 。我们综合了87个出版物的结果，这些出版物检查了试验性氮输入对土壤团聚，控制土壤C持久性的关键过程及其相关过程的影响。在全球范围内，氮输入显着增强了植物的芽和根生物量，并增加了土壤大团聚体的形成及其大小（以平均直径，MWD，P来衡量） <0.05）。出人意料的是，根部生物量和土壤团聚的N增强主要源于尿素的施用。尽管尿素输入减少了微骨料，但增加了大骨料（+ 6.9％）和MWD，这可能是由于尿素诱导的根部生长（+ 20.5％）所引起的。与此相反，其他形式的N个输入的（结合的NH ₄ ⁺，NO ₃ ^-和NH ₄ NO ₃）不影响显著根生物量，微团聚或大团聚体，但降低的微生物生物质。此外，N-二促进土壤聚合主要发生在氮输入量为中低（<200 kg N ha ^-1 yr ^-1）。总之，这些结果表明，氮肥的形式主要控制了氮对植物，微生物和土壤聚集的影响。我们的研究结果表明，尿素肥料与减少干扰（例如减少耕种）的组合可能对增强土壤聚集和有机碳的保留以及在广泛的农业生态系统中的持久性至关重要。