TRANSFORMATION OF THE GLUCOSINOLATE-DERIVED ALLELOCHEMICALS ALLYL ISOTHIOCYANATE AND ALLYLNITRILE IN SOIL

Hydrolysis of glucosinolates in Brassica tissues results in formation of allelochemicals potentially useful in controlling soil-borne plant pests. Major degradation products of glucosinolates in soil are organic isothiocyanates and nitriles; however, a clear understanding of allelochemical persistence in soil is lacking. Half-lives of allyl isothiocyanate (AI) and allylnitrile (AN) in six soils were determined using gas chromatographic analysis of ethyl acetate extracts. The half-lives for AI ranged from 20 to 60 h, whereas AN had longer half-lives of 80-120 h. AI transformation increased with reduced soil moisture and higher temperatures and occurred more rapidly in soils containing greater concentrations of organic carbon. AN transformation increased under wetter conditions and lower temperatures and occurred more rapidly in soils having higher inorganic carbon concentrations. Although different mechanisms contribute to substrate disappearance, the relatively rapid dissipation of AI and AN in soil has important implications in the control of soil-borne plant pests with Brassica tissues.