Effect of long-term fertilization on organic carbon fractions in a brown soil

In order to better understand the underlying process and mechanism of long-term fertilizations influencing SOC,the topsoil total organic carbon and its physically divided forms in a long-term located fertilizer experiment were quantified.The results indicated that long-term application of chemical fertilizer alone decreased soil FPOM-C content,but stabilized MOM-C,and increased soil TOC content.Long-term application of manure alone or combined with chemical fertilizer had more significant effect on increasing soil FPOM-C,OPOM-C,MOM-C and TOC content than chemical fertilizer application alone.As far as the proportion or ratio among the various SOC fractions studied was concerned,long-term application of manure alone or combined with chemical fertilizer increased POM-C/TOC and FPOM-C/OPOM-C,and decreased MOM-C/TOC.According to our analysis and discussion,the organic C fractionation by soil structure contributed to reveal the mechanism of long-term fertilizations affecting SOC.