| Soil Organic Carbon（SOC）is the basis of soil fertility and agricultural productivity.In recent years,the soil organic carbon content,composition characteristics and influencing factors of farmland made some progress,but due to the impact of climate and ecology,the change of farmland organic carbon is a long-term process,and the regional soil needs a longer time sequence to master the regular pattern of dynamic change of SOC;SOC is highly heterogeneous,and the conversion and accumulation of its components vary with different grouping methods.The current grouping method uses a certain physical or chemical grouping,but the association between different groups is unknown.Relevance and influencing factors are not yet clear.Yellow-mud paddy field is a kind of medium-low-yield fields widely distributed in the southern red-yellow soil area,accounting for about 40%of the area of low-yield rice fields in Fujian.In view of this,this study conducted a long-term different fertilization for 35 consecutive years(no fertilization（CK）;single application of fertilizer（NPK）;fertilizer+manure（NPKM）;fertilizer+straw total return（NPKS）.With the assistance of TOC,pellet analysis and FTIR,the dynamic changes of SOC content and reserve in the soil under different fertilization conditions and the yield were studied.Based on the physical and chemical grouping methods,this project was aimed at analyzing the characteristics,correlations and influencing factors of SOC components in soil under long-term different fertilization,revealing the dynamic changes of SOC and productivity in the yellow-mud paddy field under subtropical climate background and long-term different fertilization modes.The characteristics of organic carbon components and their correlations and the main controlling factors of SOC component changes were clarified,which had provided a scientific basis for the construction of fertilization and soil carbon pool management in the southern yellow-mud paddy field.The main results are as follows:（1）The average annual yield of rice under fertilization（19832017）increased by 63.7%-84.6%compared with CK.The yield of NPKM and NPKS increased by 12.8%and 10.7%,respectively,which were significantly different（P<0.01）,but there was no significant difference in yield between NPKM and NPKS.There was a significant positive correlation between rice yield and basic soil fertility（P<0.05）,indicating that basic soil fertility was the foundation of high yield fertilization.（2）After 35 years of continuous fertilization,the average content of soil organic carbon in CK,NPK,NPKM and NPKS increased by 1.9,3.4,7.6 and 5.7 g·kg-1,respectively,compared with the initial soil.The average content of organic carbon in the fertilized soil significantly increased by 10.3%38.9%compared with CK,and NPKM and NPKS were significantly increased by 25.9%and 14.2%,respectively,whose difference reached a significant level（P<0.05）.It showed that long-term application of organic materials,especially manure,was an important measure to increase the organic carbon content in paddy fields.（3）The soil in the southern yellow-mud paddy field was dominated by macro aggregates（>2mm）and medium aggregates（20.25mm）,and the former proportion was between 47.4%and 74.8%.Fertilization increased the percentage of medium aggregates（20.25mm）,micro aggregates（0.250.053mm）and clay aggregates（<0.053mm）.Fertilization increased the content of SOC of each aggregate.In macro and medium aggregates（>2mm,20.25mm）,NPKM significantly increased by 30.7%and 22.9%compared with NPK（P<0.05）.In clay aggregates（<0.053mm）,NPKS significantly increased by 16.7%（P<0.05）compared with NPK.Among the aggregates,the contribution rate of macro aggregates（>2mm）was the highest,accounting for 45.3%72.9%,followed by medium aggregates（20.25mm）,accounting for14.0%29.9%.（4）The long-term application of organic and inorganic fertilizers significantly increased fine-grained organic carbon（FF-C）in macro and medium aggregates（P<0.05）and increased the content of light organic carbon（LF-C）,coarse-grained organic carbon（CF-C）and mineral-bound organic carbon（mSOC）.It showed that the combination of organic and inorganic fertilizers had a better effect on FF-C.The increase of SOC was the highest with NPKM generally in macro and medium aggregates.（5）In macro and medium aggregates（>2mm,20.25mm）,LF-C,CF-C,FF-C,mSOC had significant correlation with the native SOC（P<0.01）,indicating that they were stable components in soil macro and medium aggregates organic carbon.（6）FTIR showed that SOC structure of different aggregates in the yellow-mud paddy field did not change under long-term fertilization,but the content in each aggregate changed relatively.Fertilization was generally beneficial to the accumulation of carbohydrates,aromatic carbons and aliphatic carbons in the soil of the yellow-mud paddy field,especially in the combination of organic and inorganic fertilization SOC structure of different size aggregates was different.In macro aggregates,carbohydrate content increased and aromatic carbon content decreased with the application of fertilization.Organic-inorganic application increased the aliphatic carbon content in macro aggregates,and NPKM was the most obvious.In medium aggregates,fertilization increased the content of aromatic carbon and aliphatic carbon.In micro aggregates,fertilization reduced the content of carbohydrates and aromatic carbon,while the combination of organic and inorganic fertilizers increased the aliphatic carbon content.In clay aggregates（<0.053mm）,fertilization reduced carbohydrate and aliphatic carbon content.（7）Under different long-term fertilization conditions,the correlation between SOC and its components and various influencing factors were different.The relationship between pH,bulk density,free iron oxide and SOC and its components were negatively correlated（P<0.05）.The relationship between SOC and its components and CEC,total nitrogen,microbial biomass carbon,amorphous iron oxide,activation degree,clay content were positively significant（P<0.05）.The SOC of each component in macro and medium aggregates were closely related to the yield,and the components of the macro aggregates were more obvious.In summary,long-term fertilization increased the SOC content and storage in plough layer of yellow-mud paddy field.SOC in the macro and medium aggregates had the higher contribution rate to native SOC,and the organic carbon of each component was closely related to the yield,which was a key indicator of the productivity of the yellow-mud paddy field.Fertilization,especially the combination of organic and inorganic fertilization,affected the content of SOC and the fractions and chemical functional groups of aggregates.Soil pH,bulk density,free iron oxide,CEC,and total nitrogen were closely related to SOC. |
