Organic fertilizers are essential for enhancing soil organic carbon (SOC) levels and promoting sustainable agriculture. The mechanisms of carbon sequestration in upland red soils using various organic materials are not well understood. Here, the impact of various organic fertilization strategies on SOC fractions, functional groups, iron oxides, and soil aggregates was investigated to clarify the protective mechanisms underlying SOC preservation. Six fertilization regimes were examined: no fertilization (CK), mineral fertilizer (CF), 60% mineral fertilizer (RF), RF + straw (RFS), RF + pig manure (RFP), and RF + vermicompost (RFV). The results demonstrated that SOC contents significantly increased by 62.5% in RFP and 63.1% in RFV compared to the CF treatment, with particulate organic carbon (POC) being the primary contributor. Scanning electron microscopy and X-ray photoelectron spectroscopy demonstrated that RFP and RFV treatments induced the formation of denser flock-like aggregates and increased aromatic C content, respectively. Fourier transform infrared spectroscopy analysis indicated that RFV treatment exhibited the highest abundance of functional groups among all treatments. SOC and POC were highly positively correlated with soil chemical properties, soil aggregates, poorly crystalline iron oxides, and aromatic rings. Structural equation models indicated that pig manure and vermicompost directly promoted POC accumulation, while straw provided physical protection for POC by enhancing aggregate formation. Furthermore, pig manure indirectly facilitated the development of POC and mineral-associated organic carbon via soil biochemical properties and iron oxides, respectively. Overall, the application of organic fertilizers enhanced the physical protection, mineral immobilization, and recalcitrance (alkyl C, aromatic C) of organic carbon, facilitating C sequestration and stability. This study highlights the importance of organic management in upland red soils for increasing SOC storage and maintaining global C balance.

中文翻译：

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猪粪添加促进有机碳封存，这主要是由陆地红壤中的矿物质保护贡献的


有机肥料对于提高土壤有机碳 （SOC） 水平和促进可持续农业至关重要。使用各种有机材料在陆地红壤中固碳的机制尚不清楚。在这里，研究了各种有机肥施策略对 SOC 组分、官能团、氧化铁和土壤团聚体的影响，以阐明 SOC 保存的保护机制。检查了六种施肥制度：不施肥 （CK）、矿物肥料 （CF）、60% 矿物肥料 （RF）、RF + 秸秆 （RFS）、RF + 猪粪 （RFP） 和 RF + 蚯蚓粪 （RFV）。结果表明，与 CF 处理相比，RFP 和 RFV 的 SOC 含量分别显著增加 62.5% 和 63.1%，其中颗粒有机碳 （POC） 是主要贡献者。扫描电子显微镜和 X 射线光电子能谱表明，RFP 和 RFV 处理分别诱导了更致密的羊群状聚集体的形成和芳香族 C 含量的增加。傅里叶变换红外光谱分析表明，RFV 处理在所有处理中表现出最高的官能团丰度。SOC 和 POC 与土壤化学性质、土壤团聚体、低结晶性氧化铁和芳香环呈高度正相关。结构方程模型表明，猪粪和蚯蚓堆肥直接促进了 POC 的积累，而秸秆通过促进团聚体的形成为 POC 提供物理保护。此外，猪粪分别通过土壤生化性质和氧化铁间接促进了 POC 和矿物伴生有机碳的发育。 总体而言，有机肥的施用增强了有机碳的物理保护、矿物固定化和顽固性（烷基 C、芳香族 C），促进了 C 的封存和稳定性。本研究强调了陆地红壤有机管理对增加 SOC 储存和维持全球碳平衡的重要性。