Granulated organoclay as a sorbent to protect the allelochemical scopoletin from rapid biodegradation in soil

Abstract

Allelochemicals have been proposed as environmentally friendly bioherbicides, but their short persistence in soils often limits their performance as natural weed management products. In this study, incorporation into organoclay granules was investigated as a strategy to protect the allelochemical scopoletin from rapid biodegradation and prolong its persistence in soil. The commercial organoclay Cloisite® 10A, in its raw powder form, was used to prepare the granules. A kinetic study revealed slower sorption of scopoletin on the granules than on the organoclay powder and indicated an intraparticle pore diffusion mechanism. The half-life of scopoletin in soil under laboratory conditions increased significantly by incorporating the allelochemical into the organoclay granules, from 0.34 to 14.4 days. A field experiment was also conducted to assess whether the increase in soil half-life measured under controlled laboratory conditions translated to field conditions and to compare the phytotoxicity of the granulated allelochemical with that of its free (dissolved) form. The addition of scopoletin-loaded organoclay granules to soil plots rendered a field half-life for the allelochemical of 20.1 d, in contrast to the value of 0.54 d obtained for its free form. The granules also favored the expression of the phytotoxicity of scopoletin, reducing germination and root growth of Lactuca sativa L. to a greater extent than free scopoletin. The results of this work indicate that incorporation into organoclay granules could be a suitable technological approach to provide allelochemicals with protection from rapid biodegradation losses in soil, which may help increase their persistence for a better performance as crop protection products. • Organoclay granules were assayed as sorbents of the allelochemical scopoletin (SCP). • Intraparticle pore diffusion governed SCP sorption on the granules. • Sorption on the granules provided SCP with protection from rapid biodegradation. • The granules increased SCP soil persistence under laboratory and field conditions. • The increase in soil persistence of SCP favored the expression of its phytotoxicity.