Bioavailability of Metsulfuron and Sulfentrazone Herbicides in Soil as Affected by Amendment with Two Contrasting Willow Biochars.

Abstract

This study investigated the effect of two willow (Salix spp.) biochars, produced using either fast- or slow-pyrolysis, on the bioavailability of metsulfuron and sulfentrazone herbicides in soil. Five rates (0%, 1%, 2%, 3%, and4%; w/w) of each biochar were used, along with varying rates of metsulfuron (0-3.2µg ai kg-1) and sulfentrazone (0-200µg aikg-1), followed by a sugar beet bioassay. The fast-pyrolysis biochar had minimal effect, while the slow-pyrolysis biochar decreased the bioavailability of both herbicides. Despite using the same feedstock, the two biochars had different physical and chemical properties, of which specific surface area was most contrasting (3.0 and 175m2g-1 for fast- and slow-pyrolysis biochar, respectively). Increased anionic herbicide adsorption associated with greater surface area of the slow-pyrolysis biochar is considered to be the primary mechanism responsible for reducing herbicide bioavailability with this biochar.