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.