Four long-term agricultural field experiments combined with an laboratory
incubation experiment were conducted to evaluate
the effect of organic,inorganic and organic+inorganic fertilizer application on δ13C value of
soil organic matter(SOM)and humic acid(HA)in black soil,brown soil,meadow soil and paddy soil.Compared with unfertilized control plot,δ13C value of SOM and HA decreased after the application of organic and organic+inorganic fertilizer.And in the
incubation experiment,δ13C value of SOM and HA decreased after pig manure application,but increased after corn stalk application.There are two possible reasons for these results:the δ13C value varied with different organic fertilizers,the amounts or structural compositions of SOM were changed by fertilization.Correlation analysis showed that there was no significant relationship between δ13C value and organic carbon(OC)content or structural composition of SOM and HA,but the relationship was significant between δ13C value and the increasing amount or rate of OC content of SOM.