Phenolic compounds in soil as influenced by the growth of different plant species.
Soils in which 4 grasses, 8 broadleaved species and 2 ferns had been grown individually for 16 yr were examined for p-hydroxybenzoic, vanillic, p-coumaric and ferulic acids, p-hydroxybenzaldehyde and vanillin released by 4 extractants. The amounts of phenolic compounds differed considerably among the soils. In 13 of the soils, p-coumaric acid was present in greater amounts than any of the other compounds. In soils under Pteridium aquilinum and Campanula rapunculoides the total amount of phenolic substances extracted by 2-M NaOH was 0.03% and 0.33% of the soil OM, respectively. Large differences were also found in the amounts of the phenolic compounds extracted from the roots of the 14 species. Expressed as mu g phenolic compound/g organic C, differences between the roots were greater than differences between the soils. Also, the amounts extracted by water from the roots (after freeze-drying and grinding) were much greater than the amounts extracted from the soils. With the possible exception of the soil under Elymus repens, the amounts of the identified phenolic compounds extracted by water appeared unlikely to exert allelopathic effects. However, the amounts released by 0.5% Ca(OH)2 were equivalent to conc. in the soil sol. that have been reported to have adverse effects on plant growth under certain conditions, which suggests that such effects might occur in the field as a consequence of liming.