On the allelopathic potential of certain terpenoids, phenolics, and their mixtures, and their recovery from soil

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Abstract
A study was conducted to understand the effects of certain phenolics, terpenoids, and their equimolar mixture through agar gel and soil growth bioassays and their recovery from soils. The eight compounds selected for this study were p-hydroxybenzoic acid, ferulic acid, umbelliferone, catechin, emodin, 1,8-cineole, carvone, and betulin. Lettuce (Lactuca sativa L.) was used as test species for agar gel and soil growth bioassays. Root and shoot growth of lettuce was inhibited for all the above except emodin and catechin. However, in soils treated with different phenolics and terpenoids, only root growth of lettuce was inhibited, whereas shoot growth was promoted. Recovery of p-hydroxybenzoic acid and umbelliferone was higher in unautoclaved soils, while that of catechin was lower. Recovery in relation to degradation of compounds and the significance of additive activities of compounds are discussed. Key words: phenolics, allelopathy, terpenoids, soil, Lactuca sativa.