Combined application of chemical fertilizer with green manure increased the stabilization of organic carbon in the organo-mineral complexes of paddy soil.

The influence of the combined application of chemical fertilizer with green manure on the stabilization of organic carbon (C) was explored in the organo-mineral complexes of paddy soil. The organo-mineral complexes were isolated from paddy soil treated with no fertilizer, chemical fertilizer alone, and chemical fertilizer combined with increasing amounts of Chinese milk vetch (CMV). The stability (reflected by mineralizable carbon proportion), the content and chemical composition of organic C, the Fe/Al oxides and their associated organic C in the organo-mineral complexes were investigated. The application of chemical fertilizer in combination with CMV significantly improved the stability of organic C in the organo-mineral complexes. The combined application of chemical fertilizer with CMV slightly decreased the proportion of O-alkyl C (easily decomposed) yet somewhat increased the proportions of carbonyl C and aromatic C (difficultly decomposed) and aromaticity index in the organo-mineral complexes. The treatments of chemical fertilizer combined with CMV showed more Fe oxides and Fe/Al-associated organic C and higher proportion of Fe/Al-associated organic C in the total organic C of the organo-mineral complexes. The mineralizable carbon proportion displayed significantly negative correlations with carbonyl C and Fe/Al oxide-associated organic C in the organo-mineral complexes. The Fe/Al oxides were likely to be preferentially bound with the aromatic C and carbonyl C in the organo-mineral complexes. Overall, the combined application of chemical fertilizer with CMV facilitated the association of difficultly decomposed carbon and Fe/Al oxides, which significantly improved the stabilization of organic C in the organo-mineral complexes of paddy soil.