| Summary: | Herbicide leaching is influenced by soil physical and chemical properties as well as the prevailing climatic conditions. However, little is known about leaching of mixture of herbicides in the soil, especially in tropical regions like Brazil. The objective of this study is to evaluate the leaching of 14C-mesotrione (cyclohexane-2-14C-mesotrione) alone and in a mixture with S-metolachlor and terbuthylazine in seven tropical soil columns under laboratory conditions. These soils represented a wide range of properties with varying textures, cation exchange capacity (44 to 154 mmolc kg−1), pH (6.0 to 7.7), organic carbon content (0.58 to 27.32 g kg−1) and clay mineral contents (50 to 605 g kg−1), which are typical of tropical soils. Mesotrione residues were observed across all soil column layers (0–30 cm) in all evaluated soils by simulating 200 mm of water for 48 h. The application of mesotrione, alone or in a mixture, does not influence the leaching of this herbicide. Leaching of mesotrione ranged from low (up 15 cm) to very high (up 30 cm and leachate) in the tropical soils and may pose a potential groundwater contamination risk. In sand and loamy sand soil, the mesotrione was quantified in the leachate at all sampling times as above 80% of the amount initially applied. Thus, mesotrione application without the prior knowledge of the soil physical and chemical properties can result in inefficient weed control on field condition due to high leaching potentials.
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