Iron (Fe) fertilization of the ocean mitigates global warming by sequestering carbon dioxide (CO₂) in phytoplankton, but the effect of Fe fertilization on carbon (C) sequestration in arable soils remains unknown. Iron is often added to rice paddies as blast furnace slag (BFS), a byproduct of steel manufacturing used as a silicon (Si) fertilizer to improve productivity. However, BFS also contains large amounts of Fe oxides, which might promote C sequestration by forming complexes with organic matter. To investigate this, we first analyzed data from a national survey of soils from South Korea to estimate the effect of continuous Fe addition via BFS on soil organic C (SOC) stocks. This revealed a strong positive correlation between SOC and extractable Fe and available Si concentrations, indicating that periodic silicate fertilizer application contributed to an increase in SOC stock. Second, to isolate the effect of Fe addition on SOC stocks, we conducted an incubation test with BFS enriched with Fe oxides (0–5%, wt wt⁻¹). Soil respiration was significantly reduced by silicate fertilizer application, and this effect was strengthened with the Fe-enriched fertilizer. Finally, to verify the effect of Fe addition on SOC stock changes in the field, we added three different Fe-enriched silicate fertilizers to rice paddies and quantified SOC stock changes by net ecosystem C budget (NECB) estimation. Silicate fertilizer significantly increased net primary production (NPP) by 18–20% over the control, and this effect was strengthened with increasing Fe addition. Silicate fertilizer application decreased soil respiration by 15–30% over the control, and this effect was strengthened further by Fe enrichment. As a result, silicate fertilizer application during rice cultivation increased the SOC stock by 0.65–0.68 Mg C ha⁻¹ over the control and by 0.90–0.96 Mg C ha⁻¹ for Fe-enriched fertilizer. In conclusion, the positive effect of BFS addition on SOC stock is related in part to the role of Fe oxides, primarily through the suppression of soil respiration. Fe-enriched silicate fertilizer therefore provides a management strategy to increase SOC stocks and crop productivity in rice paddies.

海洋的铁 （Fe） 施肥通过封存浮游植物中的二氧化碳 （CO₂） 来缓解全球变暖，但 Fe 施肥对耕地土壤中碳 （C） 封存的影响仍然未知。铁通常作为高炉矿渣 （BFS） 添加到稻田中，BFS 是钢铁制造的副产品，用作硅 （Si） 肥料以提高生产力。然而，BFS 还含有大量的 Fe 氧化物，它们可能通过与有机物形成络合物来促进 C 的封存。为了调查这一点，我们首先分析了韩国土壤全国调查的数据，以估计通过 BFS 连续添加铁对土壤有机碳 （SOC） 存量的影响。这揭示了 SOC 与可萃取 Fe 和有效硅浓度之间有很强的正相关关系，表明定期施用硅酸盐肥料有助于 SOC 储量的增加。其次，为了分离 Fe 添加对 SOC 储备液的影响，我们用富含 Fe 氧化物 （0–5%， wt ^wt-1） 的 BFS 进行了孵育试验。硅酸盐肥料的施用显著降低了土壤呼吸，而富铁肥料增强了这种影响。最后，为了验证 Fe 添加对田间 SOC 储量变化的影响，我们在稻田中添加了 3 种不同的富铁硅酸盐肥料，并通过生态系统净 C 预算 （NECB） 估计量化了 SOC 储量变化。与对照相比，硅酸盐肥料的净初级产量 （NPP） 显著提高了 18-20%，并且这种效果随着 Fe 添加量的增加而增强。与对照相比，硅酸盐肥料施用使土壤呼吸减少了 15-30%，而 Fe 富集进一步加强了这种效果。 因此，在水稻种植过程中施用硅酸盐肥料使 SOC 存量比对照增加了 0.65-0.68 Mg C ^ha-1，富铁肥料增加了 0.90-0.96 Mg C ^ha-1。总之，BFS 添加对 SOC 存量的积极影响部分与 Fe 氧化物的作用有关，主要是通过抑制土壤呼吸。因此，富含铁的硅酸盐肥料提供了一种管理策略，可以提高稻田的 SOC 存量和作物生产力。