Effect of long-term fertilization on organic carbon fractions and contents of cinnamon soil

【Objectives】 As an essential indicator of soil quality, soil organic carbon and its fractions play an important role in land productive capacity and crop yield. Based on a 25-year long-term fertilization experiment, effects of different fertilizing treatments on the contents of total organic carbon and its fractions in cinnamon soil were analyzed to provide scientific basis for controls of soil fertility and organic carbon management.【Methods】 Since 1988, a field experiment was conducted with eight different fertilizing treatments, no fertilizer (CK), chemical N, chemical NP, low amount organic manure, low amount organic manure plus chemical N, low amount organic manure plus chemical NP, high amount organic manure plus chemical N and high amount organic manure plus chemical NP. At the 25th year, soil samples at 0-20 cm depth of different fertilizing treatments were collected before the sowing of maize. Contents of soil total organic carbon and its fractions were determined by physical partial size fractionation method and chemical analysis. 【Results】 The results show that compared with no fertilizer application, the long-term different fertilizer application can increase the contents of total organic carbon, FPOM-C and OPOM-C in cinnamon soil, and the effect of manure combined with chemical fertilizer application, especially higher amount of manure with chemical fertilizer application is more significant. After the long-term application of M2N and M2NP, the contents of total organic carbon are increased by 121.1% and 166.8%, FPOM-C contents are increased by 239.2% and 359.2%, and OPOM-C contents are increased 288.4% and 289.9%. Compared with no fertilizer treatments, the treatments of N, M1NP and M2NP could be more suitable for the accumulation of MOM-C, which are 27.8%, 34.8%, 33.3% higher than that of no fertilizer treatment, respectively. The distribution proportions of POM-C and MOM-C in cinnamon soil are similar to those of the no fertilization. While under the long-term fertilizer application, the distribution proportions of POM-C in SOC are significantly increased, however, the proportion of MOM-C is significantly reduced. The percentage of OPOM-C in SOC has the maximum increase; as a consequence, OPOM-C is the main organic carbon pool in cinnamon soil. The correlation analysis indicates that under the long-term fertilization condition, the contents of FPOM-C and OPOM-C are highly and significantly related to each other, and they also have a strong correlation with total organic carbon content. However, MOM-C is not significantly correlated with total organic carbon and other fractions.【Conclusions】Chemical fertilizer, manure, and manure with chemical fertilizer application increase the contents of FPOM-C and OPOM-C and TOC in cinnamon soil. Higher amount of manure with chemical fertilizer application is the most effective measure to promote FPOM-C and OPOM-C, which is beneficial to nutrient availability and the quality of organic carbon. The chemical N alone and manure with chemical N, P application are better ways to increase MOM-C.