Sorption of benzoic acid onto soil colloids and its implications for allelopathy studies

The fate of allelochemicals in the soil environment largely determines the expression of allelopathy in the natural environment. In allelopathy research, the sorption of allelochemicals onto soil particles has been less well studied than their degradation. A study was carried out to evaluate the growth of cucumber (Cucumis sativus var Marketmore 76) and radish (Raphanus sativus var Crimson giant) in soil amended with 1, 5, 10 and 20 mg l(-1) benzoic acid as model allelopathic substance. Growth of both cucumber and radish was not inhibited in soil amended with benzoic acid. A labeled study indicates that sorption of benzoic acid onto soil particles increases with concentration. Benzoic acid isotherms of both soils were non-linear, with an N value of 0.875 for a garden soil and 0.891 for a garden soil + sand, and they may explain the reason for the limited allelopathic effect of benzoic acid at concentrations often recorded in natural soil.