The Interaction Of Soil Organic Carbon And Total Nitrogen Under Long-term Fertilizations In The Upland Red Soil Of Southern Of China

Soil organic matter is the core of soil fertility, and soil nitrogen exist mainly in the form of organic nitrogen in the soil organic matter. Soil C and N is the foundation for sustainable development of agriculture, and have a close relation with the global carbon and nitrogen cycles and climate change. Fertilization practices are important measures to affect the accumulation of soil carbon and nitrogen. But in the long-term fertilization, soil carbon and nitrogen accumulation were uncoupled, and the mechanism of interaction between them is uncertain. To resolve this scientific problem, based on long-term experiment in upland red soil, taking 15N labeled organic and inorganic nitrogen into the soil, through analysis the effect of different fertilization on the carbon and nitrogen fractions in soil, clearly know the distribution and movement in the different fertilization (balanced fertilizer, organic with inorganic fertilizer and only manure) , it was to illustrate the mechanism of carbon and nitrogen accumulation .The main results are as follows:(1) Long-term fertilization twenty years later, 0-20cm soil organic carbon and nitrogen content was significantly higher than that 20-40cm, 0-20cm soil organic carbon content is 1.9-3.5 times of 20-40 cm , 0-20cm total nitrogen content is 1.6-2.7 times of 20-40 cm; Only chemical fertilizer,chemical fertilizer with organic manure treatments significantly increased soil organic carbon and nitrogen content,but straw with chemical fertilizer have no significant difference wih CK; In the 20-40 cm soil subsurface, organic carbon content is between the 3.53-7.51g/kg, only NPKM (R) and M can significantly increase the organic carbon content. The total nitrogen content is in the 0.59-0.84g/kg, NPKM, NPKM (R) and M treatment were significantly higher than CK; Compared with the surface soil, long-term fertilization have a little effect on carbon and nitrogen content. Soil C/N values in the 0-20cm layer are higher than 20-40cm , 0-20cm C/N values are in the range 7.42-8.56, 20-40 cm C/N values are between 5.65-6.93.Compared with the level of initial soil carbon and nitrogen, after fertilization twenty years, organic carbon content of CK decreased 11.64% in the soil surface, The organic carbon increase rate of NPK and NPKS were significantly higher than CK, and application organic manure can growth rate between 60-70%, significantly higher than NPK and NPKS. Changes of total nitrogen and organic carbon have a great difference, the increase rate of total nitrogen is -7.24% in CK treatment, NPK and NPKS had no significant difference with CK, with manure treatment was significantly higher than the CK, the growth rate were 28-43% ;(2) Under different fertilization treatments, the surface 0-20cm of the microbial C and N content are significantly higher than 20-40cm, microbial carbon and nitrogen in the chemical fertilizer with manure,only manure treatments were significantly higher than CK in the 0-20cm soil layer, only application chemical fertilizer and chemical fertilizer with straw was no significant difference with CK. In the 0-20cm soil layer, application organic manure can increase sand, silt and clay carbon and nitrogen content. In the 20-40cm layer, application organic manure (M, NPKM, 1.5NPKM and NPKM (R)) can increase sand,clay organic carbon and nitrogen content , can decrease the coarse silt organic carbon and nitrogen content, have no significant effect on fine silt organic carbon nitrogen content; CK, NPK, NPKS treatment soil carbon and nitrogen mainly fixed in the coarse silt, carbon and nitrogen content of organic fertilizer treatment mainly combine with clay particle. Soil C/N ratio are sand> coarse silt> fine silt> clay.(3) Chemical fertilizer with manure can significantly improve the urease, catalase, and microbial activity, is conducive to the convertion of soil nitrogen. The nitrogen use efficiency are 15%-20% in the NPKM and NPK treatments, significantly higher than the only application manure (M), nitrogen use efficiency of M treatment is Only 7-9%. NPKM treatment can significantly increase the residual nitrogen and reduce losses. Residual nitrogen mainly exist in the water-soluble nitrogen forms in NPK and NPKM treatments, however M treatment mainly retained in the soil aggregates.