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 organi c isothiocyanates and nitriles; however, a clear understanding of alle lochemical persistence in soil is lacking. Half-lives of allyl isothio cyanate (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 hig her temperatures and occurred more rapidly in soils containing greater concentrations of organic carbon. AN transformation increased under w etter conditions and lower temperatures and occurred more rapidly in s oils having higher inorganic carbon concentrations. Although different mechanisms contribute to substrate disappearance, the relatively rapi d dissipation of AI and AN in soil has important implications in the c ontrol of soil-borne plant pests with Brassica tissues.