Abstract:Based on the long-term fertilization experiment conducted in a red paddy soil of Jiangxi Province, the effects of different fertilization, including no fertilizer (CK), chemical fertilizer only (NPK), and chemical fertilizer plus organic manure with low, middle and high rates (LM, MM, HM) on carbon and nitrogen contents of soil, particle organic matter (POM) and mineral-combined organic matter (MinOM) of soil fractions and their chemical structures were studied. Results showed that fertilization significantly increased carbon and nitrogen contents (P<0.05) of soil and soil fractions compared with CK treatment. Fertilization also increased the mass distribution of POM, especially under MM and HM treatments, which significantly increased by 15.7% and 25.1%, respectively. On the other hand, compared with CK treatment, fertilization significantly increased the contribution rate of POM to organic carbon by13.4%-42.6%, influenced little on C/N ratios of soil and MinOM, but significantly decreased C/N ratios of POM by 16.8%-25.0%. Furthermore, compared with NPK treatment, the chemical fertilizer plus manure treatments significantly increased POM-C to MinOM-C ratios by 27.7%-70.2%, implying manure application can improve organic matter activities. The infrared spectral analysis revealed that fertilization increased the relative contents of alkyl and aromatic C in soil by 5.4%-33.2% and 0-12.2%, respectively, compared with CK treatment. Fertilization influenced little on the content of carboxyl carbon of POM, increased alkyl C content but reduced aromatic C of POM, among of which, MM and HM treatments significantly increased alkyl C content by 12.4% and 40.6%, respectively. Besides, compared with CK treatment, fertilization increased alkyl and carboxyl C contents of MinOM except alkyl C under NPK treatment, and NPK treatment increased carboxyl C content significantly by 70.8%. These results suggest that fertilization can increase organic carbon and total nitrogen in soil and soil fractions. Combined application of chemical fertilizer with manure is propitious to improve the quantities and structure activities of POM, thus can improve soil quality.