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

Abstract

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 mg/l and 3.0 mg/l in paddy water at 0.5 days after transplanting (DAT), and 278.4 mg/kg and 81.4 mg/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 (DT 50 ) 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.

Behavior of nursery-box-applied imidacloprid in micro paddy lysimeter

“…In a similar study, uyet et al 1) observed that the average water depths were 4.2±1.9 cm and 3.9±1.9 cm in two studied plots, and the calculated input and output were about 1.2 cm/day and 1.1 cm/day, respectively. Figure 1 shows that the water balance for the actual paddy plot and in MPL of both BT and AS treatments were identical, indicating the acceptable accuracy and precision of these MPL experiments for simulating the hydrological response of an actual paddy plot.…”

“…For AS treatment, the granules are applied with soil incorporation or sandwiched together with rice seeds in soil about 14 days before transplanting. 1) e monitoring of imidacloprid in paddy water and 1-cm surface soil of experimental paddy plots has been reported in previous publications; [1][2][3] however, the residue and distribution of imidacloprid in a deeper soil layer of paddy soil has not been reported. e environmental fate of imidacloprid is rather inconsistent depending on various factors, including environmental and eld conditions, 4) and water balance has been reported as a major factor that in uences the dissipation of pesticide in rice paddy water.…”

“…e procedures and functions of AS and BT treatment were described elsewhere. 1) Imidacloprid granules were precisely weighed to appropriate amounts, and then applied to the surface of cover soil for BT treatment, and between the bed soil and cover soil for AS treatment at the recommended application rate in a nursery box (1 g a.i./nursery box). e rice seedlings were manually transplanted into nursery boxes at a density of 12 hills (3 seedlings/hill×12 hills) per MPL, which is 3-fold the normal transplanted density to ensure the detection of imidacloprid and reduce mass error due to the small scale of MPL.…”

“…All the samples were kept frozen at −20°C until chemical analysis. e S1 and S2 samples were analyzed for imidacloprid concentrations through appropriate extraction methods, the LC-MS/MS method 9) and HPLC-UV method, 1) respectively. Figure 1 shows the simulated water level, input water, and output water in MPL of both treatment methods and those in an actual paddy plot.…”

“…In general, imidacloprid concentrations in paddy water declined with time due to dilution and losses through percolation and runo 1,2) in addition to possible degradation processes such as photodegradation [17][18][19] and hydrolysis 17,19,20) in paddy water (Fig. 2).…”