Abstract:

【Objective】 In order to provide a theoretical basis for illustrating the role of humin (HM) in soil fertility, the structural characteristics of HM were studied after long-term application of organic fertilizer (pig manure) under continuous cultivation of corn in agricultural black soil, and the structural difference of HM was compared between different dosage and duration of organic fertilizer applied. 【Method】 The experiment was carried out based on a long-term fertilizer experiment of “Black Soil Fertility and Fertilizer Efficiency Long Term Monitoring Base (founded in 1980)” at Gongzhuling, Jilin Province, China. Soil (0-20 cm) was sampled at 1992 and 2005, respectively. The treatments included: CK (no fertilizer), O1 (low level of organic fertilizer at a dosage of 30 t?hm-2?a-1) and O2 (high level of organic fertilizer at a dosage of 60 t?hm-2?a-1). Soil HM were separated with NaOH-Na4P2O7 mixture, and then dashed with HF-HCl mixture. Solid state 13C cross polarization magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy was used to characterize the chemical structure of the HM isolates. 【Result】 Compared with CK, the organic carbon contents of HM increased after application of organic fertilizer; alkyl C also increased while O-alkyl C and aromatic C decreased; the ratios of alkyl C/ O-alkyl C, aliphatic C/ aromatic C and hydrophobic C/hydrophilic C all increased. The above change tendency was more obvious with the increase in the dosage and the duration of organic fertilizer applied. With the prolonged duration for the CK treatment, the organic carbon content of HM decreased. And the change tendency of alkyl C, O-alkyl C, aromatic C, alkyl C/ O-alkyl C ratio, aliphatic C/ aromatic C ratio and hydrophobic C/hydrophilic C ratio of HM from CK were all identical with that of HM from O1 and O2 with duration, but the change extents of theirs were lower in the CK treatment. 【Conclusion】The long-term application of organic fertilizer makes the HM structure tend to become more alkyl and hydrophobic, and thus is beneficial for maintaining soil fertility.

Key words: humin, black soil, long-term fertilization experiment, organic manure, solid-state 13C NMR