Abstract
Soil aggregates are the basic units of soil structure, and their composition and carbon (C) stability directly affect soil fertility. As cementing agents, humic substances play an important role in the formation and stability of soil aggregates. Long-term fertilization not only changes the structure of humic acid (HA), but also affects the content and stability of organic C in soil aggregates. In this study, based on a long-term fertilization experiment, the relationship between the molecular structure of HA and the stability of organic C in the aggregates was examined. Compared with the non-fertilization control (CK), both the application of organic manure alone (M) and organic manure combined with inorganic fertilizer application (MNPK) increased organic C content in the bulk soil and in HA. In addition, the application of organic manure (M, MNPK) favored the formation of macroaggregates (>0.25 mm) and showed a higher organic C contents of soil aggregates with different sizes than the CK. Moreover, the content of aliphatic C, the ratios of aliphatic C/aromatic C and alkyl C/O-alkyl C was increased with the application of organic fertilizer. A significant negative correlation was observed between aromatic C and organic C content of the aggregates with sizes of >2 mm, 2–0.25 mm, and 0.25–0.053 mm (P < 0.05). The findings indicated that organic fertilization treatments (M and MNPK) increased the aliphatic C content of HA, which favored the increase in the organic C content and stability of the aggregates.
Highlights
Many studies have suggested that microaggregates, especially those in the macroaggregates, play an important role in the formation and protection of C5–7
Compared with CK and NPK treatments, the content of soil humic acid (HA)-C was significantly increased by the organic fertilizer treatments (MNPK and M) (P < 0.05)
Compared with CK, organic fertilization treatments (M and MNPK) significantly increased the proportions of aggregates in the >2 mm and 2–0.25 mm fractions, and NPK treatment increased the proportions of the aggregates in the 0.25– 0.053 mm and
Summary
Many studies have suggested that microaggregates, especially those in the macroaggregates, play an important role in the formation and protection of C5–7. Plays a major role in chemical protection and decomposes slowly, which is beneficial for long-term preservation[9,10]. Studies have shown that the aliphatic C in the SOM is an important component of the stable soil C pool and plays an important role in C stability[13]. The purpose of this study was to examine the relationship between the HA-C components and the change in the organic C content of the aggregates under different fertilizations. As SOM is a continuum of progressively decomposing organic compounds[16], SOM stability as an ecosystem property was predominantly dependent on environment rather than molecular structure alone or physical recalcitrance[17]. The objective of this study was to test the relationship between soil HA-C structure and the stability of organic C in soil aggregates
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