| Soil organic carbon (SOC) is not only closely related to soil fertility and crop yield, but alsorepresents a potential carbon sink or source of atmospheric CO2.Understanding long-term effects ofdifferent fertilizations on soil organic carbon fractions and turnover characteristics is significant forimproving soil fertility and sequestering carbon. Based on a long-term fertilization experiment locatedon the red soil in Jiangxi province, by using soil organic carbon particle-size fractio method and13Cnatural abundance technology, the objective of this study was (1) to investigate effects of long-termfertilizations on SOC and its fractions;(2) to assess sources and turnover characteristics of SOC and itsfractions under long-term fertilizations and (3) to determine the allocation of new carbon and nitrogenin different particle-size fractions after organic material addition by using a laboratory incubationexperiment.Results showed that:（1）The contents of total SOC and its different fractions showed significant differences amonglong-term different fertilizations in the red soil. Compared with no fertilizer control (CK), total SOCcontent was significantly increased by17.6%and35.6%under chemical fertilizer applications (NPK&2NPK) and organic fertilizer applications (M&NPKM), respectively. Compared to CK, SOC content insand, fine silt and clay fractions were significantly increased30%,14.0%and15.1%, respectively underthe chemical fertilizer treatments, and90%,42.3%and31.4%, respectively under the mannuetreatments. Compared to CK, coarse silt-C content was not significantly changed under chemicalfertilizer treatments, but was significantly decreased18.9%~20.5%under the organic fertilizertreatments. In addition, the allocation proportion of C in sand and clay fractions reached up to19.8%and51.1%, respectively under the treatments of manure combined with inorganic fertilizer(NPKM).The optimum fertilization strategy is manure combined with inorganic fertilizer in this region.（2）Carbon input is a crucial factor to affect the turnover of SOC. A significant positivecorrelation between carbon sequestration and carbon input was found in our study. But the correlationwas not consistent for different particle-size fractions. Carbon stocks in clay and sand fractionsgradually increased with increasing carbon input, but the increase rate (202.6%) in clay fraction wassignificantly higher than in sand fraction (97.6%). This indicated that clay was the main components forcarbon sequestration in the red soil. Mean conversion efficiency of carbon input into SOC was8.1%。The results suggest that SOC did not reach saturation in the red soil and it had the potential for carbonsequestration.（3）The result showed that the rate of carbon derived from corn for CK and NPK treatmentgradually increased with the time, reaching28.5%and29.6%, respectively, which indicated that the rateof carbon derived from corn may reach a stable after24year. δ13C values gradually increased from largeparticles to small particles. Compared with CK in1992, δ13C values of CK and NPK treatments indifferent fractions was significantly improved, suggesting that the content from corn increased and theupdate change of SOC was accelerated by fertilization in different particle-size fractions.（4）The incubation experiment results showed carbon mineralization rate (CMR) was highest inthe treatment of adding a high amount of corn straw (1%S), reaching to25%.CMR in the treatment of adding corn straw was higher than that in the treatment of adding carbon-equal pig manure. There was asignificance for carbon sequestration and improving soil fertility.（5）Carbon derived from added corn straw was mostly allocated in250-2000μm aggregates.13Cnatural abundance revealed that turnover rate of organic carbon in large aggregates was faster than thatin small aggregates. Nitrogen derived from15N-labeled pig manure was mostly stored in53-250μmsize aggregates.In conclusion, the optimum fertilization strategy was manure combined with inorganic fertilizer inred soil.The update change of SOC was accelerated by fertilization. Carbon derived from adding cornstraw was mostly allocated in large aggregates. |
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