Effect Of Long-term Fertilization On Organic Carbon Fractions And Turnovers Of Cinnamon Soil

Based on 25 years long-term fertilization experiment, effects of 8 different fertilizing treatments on total organic carbon content, fractions, characteristics of soil organic carbon mineralization, and soil enzyme activity in cinnamon soil were analyzed by indoor determination and incubation experiment to provide scientific basis for controls of soil fertility and organic carbon management. The 8 treatment models are no fertilizer treatment （CK）, only nitrogen fertilizer （N）, nitrogen and phosphorus co-applied （NP）, low amount of organic manure （M1）,low amount of organic manure and nitrogen fertilizer （M1N）, low amount of organic manure and nitrogen and phosphorus co-applied （M1NP）, high amount of organic manure and nitrogen （M₂N）, high amount of organic manure and nitrogen and phosphorus co-applied （M₂NP）. The results showed that:1 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 the of no fertilizer treatment, respectively.2 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 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.3 Under this culturing condition, the mineralization rate of soil organic carbon of different treatment all reached their peak on first day, then presented a sharp decrease. After 5 days cultivation, the decrease tended to be slow, and the CO₂ producing rate gradually came to accordance. During the cultivation, the change of mineralization rate of soil organic carbon of each treatment fitted with the logarithmic function relationship. Long-time using of different fertilization could all enhance the mineralization rate of soil organic carbon. The enhance order is:manure with chemical fertilizer application> only manure> only fertilizer> CK. After 57 days of cultivation. CO₂-C cumulative evolved amounts range of different treatment is 555.0-980.3mg/kg. The M₂NP and M1N are the highest ones with 1.77 and 1.73 fold higher than CK.4 Under the long-time fertilization condition, the percentage of CO₂-C accumulative production in TOC presents a decreasing trend. The M₂NP treatment showed the most obvious decrease with 6.3% lower than the CK. The potential CO₂-C production of fertilization treated soil are all higher than CK, especially for the M1N, and M₂NP which are 923.7mg/kg and 926.4mg/kg,74.0% and 74.5% higher compared with CK. The fertilization treatment could increase the turnover rate of soil organic carbon significantly and reduce the turnover time, M1NP、M₂NP showed the most significant effect on it. CO₂-C accumulative production is significantly related to TOC, FMOM-C, OPOM-C, and POM-C, but there is no obvious relationship with MOM-C5 With long-time using of different fertilization, the activities of Urease, Invertase and Cellulase enhance significantly, and the organic fertilization effect is better than chemical fertilization. M1NP and M₂NP showed the strongest effect on the improvement of Urease, Invertase activities with 117.8%、134.0% increase for Urease, 178.0% and 183.2% increase for Invertase. M₂N and M₂NP showed the strongest effect on Cellulase activities, and there are 313.1% and 334.9% increase compared with CK. There is no significant effect of single chemical fertilizer and manure application on activity of Hydrogen peroxidase. However, the combined application of chemical and organic fertilizer could increase the activities of Hydrogen peroxidase. The M₂NP showed the most significant effect with 4.8% raise compared with no fertilization.6 Related analysis reveals that under the long-term fertilization, the activities of Urease, Invertase, Cellulase and Hydrogen peroxidase present significant correlations with each other. They also have a strong correlation with TOC, FMOM-C, OPOM-C, POM-C, and CO₂-C accumulative production. But there is no obvious relationship with MOM-C.In the actual production, the purpose is improving the efficient of soil nutrition as well as optimizing quality of soil organic carbon, and enhancing the soil carbon sequestration capacity. In this research M₂NP treatment showed respectively outstanding functions, which means it is possible to choose M₂NP for the test area.