Objective  In general, it is poor structure and lower organic carbon content in red soil. Soil organic carbon (SOC) is the key indicator for affecting soil structure. However, lot of studies were focused on the relationship between SOC and aggregates. It was unknown that the regulation mechanism of SOC on aggregate.

  Method  Based on the long-term experiment in red soil which started in 1986. Five treatments were selected: No fertilizers (CK); mineral nitrogen and phosphorus (NP); mineral nitrogen, phosphorus, and potassium (NPK); NPK plus pig manure (NPKOM); pig manure only (OM). Soil in 0-20 cm was sampled after early corn harvested in 2019. SOC content and its chemical structure, aggregate components were measured and analyzed. The correlation between the chemical structure of SOC and aggregates was further quantified.

  Result  Compared with CK, SOC content under NPKOM and OM was increased by 51.63% and 34.34%, respectively; the proportion of alkyl carbon and alkoxy carbon in NPKOM was increased by 29.85% and 21.54%, respectively; they were increased by 31.98% and 28.81%, respectively, in OM. But the proportions of aromatic carbon and carboxyl carbon in NPKOM and OM were decreased. Compared with CK, the aromaticity of NPKOM and OM was reduced than CK by 24.90% and 25.19%, respectively. While, the aliphatic carbon and aromatic carbon ratio were increased by 64.87% and 73.34%. Meanwhile, the mean weight diameter (MWD) under all the treatments with fertilizer (NP, NPK, NPKOM and OM) was significantly higher than that under CK. SOC, aliphatic carbon, and aromatic carbon ratio were positive correlated with MWD, while the aromaticity was negative correlated with MWD.

  Conclusion  Manure application was an optimum management to improve SOC chemical structure. The ratio of alkyl carbon and alkoxy carbon, aliphatic carbon and aromatic carbon were increased, but the aromaticity was reduced. Therefore, the soil structure was improved by SOC accumulation and MWD promotion.