The content and effects of coumarin in the aqueous extract of yellow sweet clover

The objective of this study was to determine the content of coumarin in the aqueous extracts of yellow sweet clover (Melilotus officinalis) and evaluate its allelopathic effect on weeds. Liquid chromatography-mass spectrometry (LC/MS) was employed to determine the content of coumarin in the aqueous extract of yellow sweet clover. Laboratory bioassay was conducted to evaluate the effects of different concentrations of coumarin on seed germination and seedling growth of Italian ryegrass (Lolium multiflorum), grainamaranth (Amaranthus hypochondriacus), barnyardgrass (Echinochloa crus-galli), common knotgrass (Polygonum aviculare), alfalfa (Medicago sativa “Victoria”), red clover (Trifolium pratense) and yellow sweet clover. The results showed that content of coumarin in the aqueous extracts of yellow sweet clover was 46.7 μg·mL-1, accounting for 1.152% of total dry matter of the aqueous extract. At the concentration of 40 μg·mL-1, coumarin significantly inhibited (P0.05) seed germination and seedling growth of Italian ryegrass, common knotgrass, red clover and alfalfa. At the concentration of 80 μg·mL-1, coumarin significantly inhibited (P0.05) both the seed germination and seedling growth of all the tested plants except with a promotion on the seed germination of grainamaranth, and completely inhibited seed germination and seedling growth of ryegrass seed, common knotgrass and red clover. These results suggested that there were high content of coumarin in aqueous extract of yellow sweet clover which had different allelopathic effects varied with weeds species.