Abstract:The effects of pig manure (PM) on structural characteristics of fulvic acids (FAs) from brown soil were studied in a longterm field experiment The results showed that the O/C ratio, Δlogk and the content of carbonyl-C of FAs all decreased; Whereas, the C/H ratio, RF, the absorption intensity at 2936cm-1 and 1639cm-1, the contents of aromatic-C and alkyl-C of FAs were increased after the application of PM It indicated that the oxidative degree decreased, but the condensation degree and the relative content of aliphatic components increased in the molecule of FAs from brown soil Thus, the molecular structure of FAs tended to become more complex and aliphatic after the application of PM