Organic carbon preservation promoted by aromatic compound-iron complexes through manure fertilization in red soil

This study was aimed at evaluating the effect of manure fertilization on organo-mineral complexes based on unfertilized (CK) and 5-year manure fertilization (M) in red soils (ultisols). Sequential density fractionation was adopted to obtain particular organic matter (POM, 2.6 (MOM> 2.6)), which were demineralized by hydrofluoric acid (HF). The HF-dissolved organic carbon (OC) was identified as mineral bound OC, and was characterized by comparing the band area of Fourier transform infrared spectroscopy before and after 10% HF demineralization. Manure fertilization significantly increased the OC and nitrogen contents of bulk soil, POM, MOM1.8–2.2, and MOM2.2–2.6, but did not affect MOM> 2.6. About 82.9–86.1% soil OC was retained by MOM1.8–2.2 and MOM2.2–2.6 dominated with iron (Fe) and aluminum oxides and phyllosilicates, in which HF-dissolved OC was significantly positively correlated with poorly crystalline (Feo) (R2 = 0.61, P 2.6 was composed of aromatic C, amide N, and polysaccharides, not being affected by fertilization. Our results suggested that manure fertilization promotes organo-mineral association, particularly for aromatic compound-Fe complexes, contributing to OC preservation in red soils.