摘要：

Background and Aims Amendment of soil by biochar may reduce efficacy of soil-applied herbicides due to sorption . Methods Bioassays with Green Foxtail ( Setaria viridis ) tested the influence of two biochars on phytoavailability of S-metolachlor and sulfentrazone under biochar amendment of 0, 13, 26 and 52Mgha -1 . Results Adsorption of both herbicides was an order of magnitude greater on a high specific surface area (SSA) biochar (EUC-800; SSA 242m 2 g -1 ) than on a low SSA biochar (BC-1; SSA 3.6m 2 g -1 ). Herbicide doses near the lowest recommended label rates controlled the weed at 13 and 26Mgha -1 of BC-1; sulfentrazone was also effective at 52Mg BC-1ha -1 . These same herbicide doses controlled weed germination and development only at 13Mgha -1 of EUC-800; at herbicide doses near the highest label rates, weed control was also achieved at 26Mg EUC-800ha -1 , but not at 52Mg EUC-800ha -1 . Conclusions Increased doses of soil-applied herbicides cannot necessarily offset decreases in herbicide phytoavailability in biochar-amended soils, particularly if the biochar has a high SSA. Considering the long half-life of biochar in soil, pest control needs will be best served by low SSA biochars.

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