Effect of Organic Matter Application on CP-MAS-13C-NMR Spectra of Humic Acids from a Brown Soil

Organic matter (OM) applications can influence the amount and structural characteristics of humic acid (HA). The objective of this paper was to clarify the effect of long term OM application on the changes of structural characteristics in HAs, which provided new information for improving soil fertility by OM application. The experiment was carried out on a brown soil at Shenyang Agricultural University, Liaoning province, China. The experiment included three treatments: zero-treatment (

CK

br

), and two pig manure (PM) treatments (

O

1

and

O

2

) at the rates of 0.9 t·ha

−1

and 1.8 t·ha

−1

of organic carbon, respectively. The samples of the HA fraction were extracted, separated, purified and characterized by elemental composition, differential thermal analysis (DTA), δlg

K

value and CP-MAS-

13

C-NMR. The results indicated that the CP-MAS-

13

C-NMR spectra of the HA were quite similar to each other. But after OM application, the contents of alkyl C and O-alkyl C increased and the contents of aromatic C and carbonyl C decreased in HAs, indicating that the OM application decreased the content of aromatic C and was simplified the molecular structure in HAs.