Determination of oxadiazon residues in the field treated soil with and without organic matter incorporated

The behavior of oxadiazon (5-tert-butyl-3-(2,4-dichloro-5-isopropoxyphenyl)-1,3,4-oxadiazol-2 (3H)-one) in the soil may be influenced by organic material content. The objective of this study was to chromatographically determine soil oxadiazon residue content as a function of organic material and soil depth. A randomized block design was used, with treatments arranged in a scheme comprising 2 × 4 × 8 + 1 sub-subdivided plots with four repetitions. Plots were comprised of soil with (8 t ha⁻¹) and without organic material incorporated, together with a control (0 t ha⁻¹ and 0 g ha⁻¹ of oxadiazon). Subplots were based on soil depth (0.00–0.05; 0.05–0.10; 0.10–0.15 and 0.15–0.20 m) and sub-subplots on soil collection time (0, 2, 4, 8, 16, 32, 64 and 128 days after application—DAA). Oxadiazon was applied at 1 kg ha⁻¹. For residue determination, samples were quantified via high performance liquid chromatography (HPLC) using the solid–liquid extraction with low temperature partitioning (SLE-LTP) technique. In the superficial layer at 0.00–0.05 m, dissipation t _1/2 of oxadiazon took between 56 and 51 days in soil with and without organic material incorporated, respectively. Oxadiazon was found in the upper layer (0.00–0.10 m) of soil until 64 DAA and did not occur at any other depth, demonstrating low soil mobility potential. In soils containing incorporated organic material, higher concentrations of oxadiazon were observed over different depths and evaluation periods.