Effect of formulations and treatment methods of nursery boxes applied with insecticide on the behavior of imidacloprid in rice paddy fields

The behavior of imidacloprid was investigated in two paddy plots with conventional release granular formulation and controlled release granular formulation corresponding to before transplanting (BT) treatment and at sowing (AS) treatment (14 days before transplanting) in nursery boxes, respectively. The maximum concentrations of imidacloprid were 30.2 μg/l and 3.0 μg/l in paddy water at 0.5 days after transplanting (DAT), and 278.4 μg/kg and 81.4 μg/kg in 1cm paddy surface soil at 1 DAT for BT and AS treatments, respectively. Dissipation of imidacloprid from paddy water and 1 cm paddy surface soil can be described by biphasic first-order kinetics in the water and single phase first-order kinetics in paddy soil. The half-lives (DT50) of imidacloprid in BT and AS treatments were 2.0 days, 2.4 days during the first phase (7 days) in paddy water, and 12.7 days and 11.0 days in paddy soil, respectively. AS treatment with controlled release granular formulation had lower concentrations of imidacloprid in paddy water and surface soil and has the potential to pose a lower environmental risk than BT treatment with conventional release granular formulation.