Cow bone char as a sorbent to increase sorption and decrease mobility of hexazinone, metribuzin, and quinclorac in soil

Hexazinone, metribuzin, and quinclorac herbicides are used extensively throughout Brazil, and they can easily be leached to groundwater sources. Bone char (BC) has been shown to strongly sorb organic compounds and could be used as a sorbent to increase herbicide sorption and decrease leaching, although the better form of application is not known. The aim of this research was to assess the effect of cow BC on the sorption-desorption and mobility of hexazinone, metribuzin, and quinclorac applied to a sandy loam tropical soil under laboratory conditions. The methodology of the sorption-desorption studies was established using a batch equilibrium method, and the treatments were unamended soil, pure BC, and BC-amended soil (at a rate of 5% by weight). Herbicide mobility studies were evaluated by column leaching and soil thin-layer chromatography (TLC). In the column leaching studies, BC was either applied to the surface or incorporated into the 0-10 cm top layer of soil, the latter at a rate of 5% by weight (60 t ha(-1)). A glass column was prepared for each treatment, and analyses of C-14-herbicides were performed by liquid scintillation counting. Finally, for TLC studies the BC treatments were unamended soil, BC (5% by weight)-amended soil, soil + BC band (1 cm) in the middle, and soil + BC band at the top. We conclude that cow BC is an excellent sorbent to reduce mobility of hexazinone, metribuzin, and quinclorac in a tropical soil through the high sorption of these herbicides, regardless of application form of the material. Thus, it is possible to minimize the pollution of soil-applied herbicide simultaneously, as the BC and thus the herbicides can remain in the soil for a long time.