The role of iron oxides in the preservation of soil organic matter under long-term fertilization

PurposeThe aim of this paper is to enlighten the role of highly reactive iron (Fe) minerals in soil organic carbon (SOC) preservation in soil aggregates.Materials and methodsThe effects of four long-term (37-year) fertilization regimes (NPK, chemical fertilization; NPKM, chemical fertilization + cattle manure; M, cattle manure; CK, non-fertilization control) on organic carbon (OC) stability, soil iron fractions in bulk soil, and soil aggregates were studied to characterize the capacity and mechanism of Fe minerals to preserve SOM in soil.Results and discussionLong-term fertilization significantly altered the Fe fractions in soil and soil aggregates. The two applications with manure (NPKM and M) increased the non-crystalline Fe content, while the chemical fertilizer (NPK) increased the crystalline Fe content. Besides, long-term fertilization with manure greatly increased the content of SOC and soil total nitrogen (STN). The non-crystalline Fe was positively correlated with the SOC content in both soil and soil aggregates. Meanwhile, the long-term fertilization treatments greatly changed the mass distribution and OC content of soil aggregates.ConclusionsLong-term manure fertilization promoted the formation of non-crystalline Fe fractions, which bounds to SOC to form soil macro-aggregates. Thus, the formation of SOC-Fe association in soil and soil aggregates plays a crucial role in SOC preservation.