Determining the effect of soil properties on the stability of scopoletin and its toxicity to target plants

The sorption of the allelochemical scopoletin (7-hydroxy-6-methoxycoumarin) was studied in eight agricultural soils and different model sorbents. We also determined its degradation in selected soils and related sorption and degradation results to the expression of scopoletin phytotoxicity in soil towards two model plant species, Eruca vesicaria and Hordeum vulgaris. Scopoletin was sorbed to a greater extent in acid soils than in alkaline soils. Correlations with soil properties indicated that the soil pH and fine (silt/clay) fraction played a primary role in the sorption of scopoletin by soils. Weak interactions controlled its sorption in acid soils, whereas stronger interactions, probably with mineral clay constituents, became more relevant in alkaline clay soils. Dissipation of scopoletin in the soils was microbial-mediated and occurred more slowly in acid than alkaline soils. As a result, the phytotoxic activity of scopoletin was expressed in acid but not in alkaline soil. The results point to the influence that soil properties are expected to exert on the expression of the phytotoxicity of scopoletin in natural and agricultural ecosystems.