RESUMO
Soil macro-aggregates are the main location for soil organic carbon ï¼SOCï¼ sequestration, which is of great significance to improve soil fertility. This study aimed to understand the mechanisms of the organic carbon ï¼OCï¼ sequestration in macroaggregates and improve crop yield in wheat fields on the loess plateau. With the aggregate-density fractionation method, an eight-year experiment was conducted to investigate the following three factorsï¼ â the effects of long-term fertilization on OC fractions within macroaggregatesï¼ â¡ the variation characteristics of OC fractions within macroaggregates, including coarse particulate organic carbon ï¼cPOCï¼, fine particulate organic carbon ï¼fPOCï¼, intra-microaggregate particulate organic carbon ï¼iPOCï¼, free silt and clay particulate carbon ï¼s+c_fï¼, and intra-microaggregate silt and clay particulate carbon ï¼s+c_mï¼ï¼ ⢠and the relationships between them and SOC input and yield formation. The treatments included no fertilization ï¼CKï¼, farmer pattern ï¼NPï¼, optimized fertilizers pattern ï¼NPKï¼, optimized fertilizers + organic fertilizers pattern ï¼NPKMï¼, and optimized fertilizers + biological organic fertilizers pattern ï¼NPKBï¼. The results showed that the application of organic and chemical fertilizer ï¼NPKM and NPKBï¼ improved significantly the SOC content in macroaggregates compared with that in the single fertilizer treatment ï¼NP and NPKï¼, which had a greater increase in SOC content in macroaggregates than that of the soil. All fertilization treatments had a tendency to increase the content of fractions iPOC, fPOC, and iPOC in macroaggregates, but silt and clay carbon ï¼s+c_f and s+c_mï¼ contents were decreased. The application of manure combined with chemicals markedly increased the allocations of fractions cPOC, fPOC, and iPOC reserves, but it greatly decreased ï¼s+c_fï¼ reserves allocation. However, the application of chemical fertilizers only significantly increased the proportion of cPOC reserves in macroaggregates. Correlation analysis showed that there were significant positive correlations among wheat grain yield and OC fractions ï¼cPOC and fPOCï¼ contents, SOC content, the OC content of >0.25 mm macroaggregates, and SOC input, and the correlation coefficient was 0.645-0.883. In conclusion, long-term fertilization, especially combined with organic fertilizer, could promote the free silt and clay carbon fraction ï¼s+c_fï¼ to transfer into other forms of OC components through the increase in soil carbon input in the wheat field of the loess plateau. Furthermore, the OC content of macroaggregates was increased overall, providing a good soil environment for crop yield.