The qua
litative and quantitative characteristics of soi
l organic carbon (SOC) and re
lated humic acids(HAs) extracted from the soi
ls of fie
ld p
lots were investigated after 8 years of annua
l paddy (
Oryzasativa L.) and up
land maize (
Zea mays L.) rotation with various ferti
lizations. Seven ferti
lizationtreatments were se
lected: C
k (no inputs); Chem (chemica
l ferti
lizer of NPK); Comp (swine compost);Comp + 33% of Chem N rate; Comp + 67% of Chem N rate; GM (
legume green manure) + 33% ofChem N rate; and peat + 33% of Chem N rate. Organic and inorganic nitrogen inputs of six treatmentswere equiva
lent with respect of nitrogen content, but Comp, GM, and peat treatments werecomp
lemented with various amounts of inorganic N. After harvest of the eighth
paddy crop, surfacesoi
l samp
les co
llected from the p
lots were subjected to soi
l characterizations and extraction of humicsubstances, which were used for chemica
l, spectroscopic (FTIR,
13C NMR, ESR, X-ray diffractometry),
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13C, and
14C dating ana
lyses. The yie
lds of HAs extracted from the seven treatments were significant
lydifferent. Treatment containing persistent organic compound such as the peat + 33% N treatmentincreased the humification process in topsoi
ls and produced higher yie
ld of HA. Spectroscopic ana
lysesrevea
led that ferti
lization treatments
changed the functiona
l groups, a
lky
l C, crysta
lline characteristics,and
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13C ratios of HAs and turnover rate of SOC considerab
ly. The SOC of the peat + 33% Ntreatment had the highest mean residence time of 3100 years. Various ferti
lizer treatments arecorre
lated with turnover rate of SOC and re
lated HAs, which are associated with concerned carbonsequestration as we
ll as mitigation of CO
2 emission in the soi
l environment.