Biochar Soil Additions Affect Herbicide Fate: Importance of Application Timing and Feedstock Species.

Biochar (BC), solid biomass subjected to pyrolysis, can alter the fate of pesticides in soil. We investigated the effect of soil amendment with several biochars on the efficacy of two herbicides, clomazone (CMZ) and bispyribac sodium (BYP). To this aim, we evaluated CMZ and BYP sorption, persistence, and leaching in biochar-amended soil. Sorption of CMZ and BYP was greater in soil amended with BC produced at high temperature (700 degrees C). Significant sorption of the neutral CMZ herbicide also occurred in amended soil with BC prepared at low temperature (350 and 500 degrees C). For both herbicides, desorption possessed higher hysteretic behavior in soil amended with BC made at 700 degrees C (pyrolysis temperature). Dissipation of CMZ was enhanced after addition of BCs to soil, but no correlation between persistence and sorption was observed. Persistence of BYP was up to 3 times greater when BC made at 700 degrees C was added to soil. All BCs suppressed the leaching of CMZ and BYP as compared to the unamended soil. Amendment with 700 degrees C BC inhibited the action of CMZ against weeds, but 350 and 500 degrees C BCs had no such effect when added to soil. BYP activity was similar to that exhibited by unamended soil after the addition of 700 degrees C BC. Froth these results, biochar amendments can be a successful strategy to reduce the environmental impact of CMZ and BY? in soil. However, the phytotoxicity of soil-applied herbicides will depend on BC sorption characteristics and the pesticide's chemical properties, as well as the pesticide application timing (e.g., pre- or posternergence). According to our results, proper biochar screening with intended pesticides in light of the application mode (pre- or postemergence) is required prior to use to ensure adequate efficacy.