Abstract: 【Objective】The effects of long-term fertilization on the distribution of organic carbon (OC) and total nitrogen (TN_OIC) of organo-mineral complexes in red paddy soil were studied, which provided a basis for long-term management and cultivation of soil fertility in red paddy soil. 【Method】The red paddy soils in long-term fertilization experiment were studied (Since 1984), which include four treatments: no fertilization (CK); inorganic P and K fertilizers (PK); inorganic N, P and K fertilizers (NPK) and NPK plus manure (NPKM, 70%NPK plus 30% manure). Soil samples of 0-20 cm were collected and the distribution of organo-mineral complexes at each particle level (<2 μm, 2-10 μm, 10-20 μm, 20-50 μm, 50-250 μm) was analyzed. The effects of fertilization on the content, storage of organic carbon and total nitrogen as well as the carbon-nitrogen ratio (C/N) were discussed. And the effects of SOC and TN contents in organo-mineral complex on contribution rate of SOC and TN contents in red paddy soil.【Result】Compared with the CK treatment, fertilization treatment significantly increased the particle size ratio of 20-50 μm and decreased the particle size ratio of <10 μm. Compared with other fertilization treatments, NPKM treatment increased the proportion of 50-250 μm grain size complex more significantly. Different fertilization had different effects on the content of OC and TN_OIC in grain size. Compared with PK, the content of OC and TN_OIC in grain size from 50 μm to 250 μm under NPK treatment increased 36.3% and 80.6%, respectively.  Compared with NPK, the content of OC and TN_OIC in 50-250 μm granular complex increased by 35.4% and 19.5% in NPKM treatment, respectively. The SOC and TN_OIC storage of the organic and inorganic complexes were mainly distributed at the 10-20 μm particle level. And fertilization significantly reduced the storage of <2 μm particle-level complex OC and TN_OIC, but increased the storage of OC and TN_OIC at 20-50 μm particle-level. Compared with PK treatment, the OC storages of <2 μm and 50-250 μm particle-level complexes treated by NPK increased by 18.5% and 31.2%, respectively, and the storages of TN_OIC increased by 18.8% and 73.7%, respectively. Compared with NPK, the NPKM treatment reduced the SOC and TN storages of the <2 μm particle-level complex by 25.6% and 27.4%, respectively, while OC and TN_OIC storages of 50-250 μm particle-level complex increased by 56.3% and 38.6%, respectively. Fertilization significantly influenced the C/N ratio of 50-250 μm particles. Compared with PK, the C/N ratio of 50-250 μm fraction treated with NPK decreased by 24.6% and compared with NPK, the C/N ratio of 50-250 μm fraction treated with NPKM was increased by 13.4%. Fertilization significantly affected the contribution rate of organo-mineral complexes of each particle size to soil SOC and TN content. Compared with PK, the contribution rate of NPK treatment 50-250 μm particle-level complex to SOC and TN increased by 17.4% and 47.4%, respectively. Compared with NPK, the contribution rate of NPKM treatment 50-250 μm particle to SOC and TN were reduced by 39.5% and 32.8%.【Conclusion】In red soil paddy soil, long-term fertilization promoted the formation of large-grain organo-mineral complexes. The nitrogen input in the chemical fertilizers significantly increased the grain-level organic carbon, total nitrogen content and storage of the granular grade of 50-250 μm. The organo-mineral combined application is conducive to increasing the soil organic carbon content and the proportion of large-grain organo-mineral complexes, which is helping to preserve the inorganic nitrogen fertilizer applied. Therefore, organic and inorganic compound application is an effective measure for long-term fertilization management of red paddy soils.  

Key words: long-term fertilization, red paddy soil, organo-mineral complex, organic carbon, total nitrogen