Abstract: Humus is a specific kind of organic matter widely distributed in soils. The characteristics of humus have significant impacts on the fate of pollutants in the environment. In this study, we examined the effects of fertilization modes from rice rotation systems on the contents, spectral properties, photochemical activity, and photosensitization of quinclorac (QNC) of humic (HA) and fulvic acids (FA). The results showed that under the rice-vegetable rotation system, organic fertilizer treatment decreased the humification degree and molecular weight of HA, but increased the number of oxygen-containing functional groups and the abilities of photoproducing hydroxyl radical (HO·), singlet oxygen (¹O₂) and photosensitizing QNC, compared with chemical fertilizer treatment. Under organic fertilization mode, the molecular weight of FA was increased, but the number of redox functional groups and the abilities of photoinducing HO· and ¹O₂ and photosensitizing QNC were decreased. Under rice-shrimp cultivation system, organic-inorganic fertilizer treatment increased the humification degree, molecular weight, number of redox functional groups and oxygen-containing functional groups, and ¹O₂ photogeneration of HA, but decreased the abilities of photoproducing HO· and photosensitizing QNC, as compared with chemical fertilizer treatment. The humification degree and molecular weight of FA under organic-inorganic fertilization mode were increased, while the abilities of photoproducing HO· and ¹O₂ and photosensitizing QNC were decreased. In conclusion, organic fertilization could enhance the photochemical activity and photosensitizing efficiency of humus, and further promote the photodegradation of QNC in the environment.

Key words: fertilization mode, humus, quinclorac, photodegradation.