The Characteristics Of Soil Organic Carbon Fraction Under Different Carbon Saturation In Different Long-term Fertilization

Soil organic carbon(SOC)is an essential index for soil fertility,and also is the foundation of the crop productivity.The external C input is the major way to increase SOC content.The SOC content is not infinite,the maxmum level exist,that is the C saturation.Two different C saturation level soil,paddy soil and fluvo-aquic soil were chosen to explore the characteristics and mechanism of C saturatuion.The basic soil properties,soil fractions by physico-chemical method,SOC structure characteristics by FTIR(fourier transform infrared spectroscopy)and labile SOM components were mearsured and analyzed.The main results showed as follows:(1)Compared to initialsoil,the p H in paddy soil declined,while p H in fluvo-aquic soil changed little.The total nitrogen(TN)content was significantly increased by103%-179%,105.9%-113.2% in paddy soil and fluvo-aquic soil,respectively available(AK)content in paddy soil decreased,while which increased in fluvo-aquic soil.The available nitrogen(AN)content changed little in paddy soil,while 25.9%-51.8% increased in fluvo-aquic soil.The available P(AP)increased376%-474% under pig manure fertilization in paddy soil,and increased by 277.9%,188.3% under organic fertilizer treatment and high nitrogen fertilizer in fluvo-aquic soil.(2)Mineral and manure fertilizer combination significantly improved the storages of total SOC(TOC)and SOC content in different fractions.Compared with no fertilizer treatments(CK),TOC storage was significantly increased 103%-179%,105.9%-113.2% in paddy soil and the fluvo-aquic soil,respectively.At paddy soil,The non-protected C pool and physically-protected C pool appeared non-linearlly with cumulative C input,which tended to saturation.while the T chemically-protected C pool and biochemically-protected C pool were linearlly increase with cumulative C input.In contract,at fluvo-aquic soil,the C pool in each fraction showed linearlly increase with cumulative C input.Generally,the non-procteced and physically-proctected C pool transferred to chemically-and biochemically-protacted C pool with SOC increase.The former one was more sensitive for SOC dynemics.(3)The SOM had almost the same C skeleton under different treatments,but the types of functional groups and the absorption intensity demonstrated different.The inert substance such as polymer of aliphatic,aromatic,polysaccharide and organic silicon compounds increased under mineral and organic fertilizer combination treatments.can significantly increase the soil(4)The labile SOC increased under organic material application treatments in paddy soil.The highly and lowly SOC was highest in treatments with green manure and straw in paddy soil with value as 3.02 g/kg and 16.16 g/kg,respectively.And the highly and lowly SOC was1.68 g/kg and 13.68 g/kg,respectively in fluvo-aquic soil.Generally,SOC tended saturation in paddy soil,but did not in fluvo-aquic soil The data indicated that the hight application rate of manure combined with chemical fertilizer is the most effective parctice for increasing the SOC content.