The specific objectives of this research are: to investigate the applicability of the RICEWQ model in Korean conditions; to conduct scenario analysis under different water and pesticide conditions using the RICEWQ model; to assess the molinate risk fo ...
The specific objectives of this research are: to investigate the applicability of the RICEWQ model in Korean conditions; to conduct scenario analysis under different water and pesticide conditions using the RICEWQ model; to assess the molinate risk for adjacent aquatic organisms various scenarios; to propose an appropriate withholding period of discharge water from the paddy plot through a risk assessment, in order to prevent adverse effects on populations; and to propose best management practices(BMPs) for ecosystem conservation.
Results to predict the molinate concentrations in rice paddies and to examine the potential of pesticides contaminate water resources under realistic local agricultural scenario are summarized following.
1. In order to calibrate the RICEWQ model, an experimental paddy plot of 0.2ha(100×20m) at Seobyeon-dong, Daegu, in Korea was selected. Field observation was performed from 4 June to 2 September 2006. Molinate that a selective thiocarbamate herbicide used to control broad-leaved and grassy plants in rice was selected. Field observation was performed from 4 June to 2 September 2006. The results of the model simulation were well matched to the observed water depths(Fig. 5-4). The ponded water depths had an RMSE of 0.537cm, and the REE was 0.301cm. The low RMSE and REE values, and the high EF(0.909) and CNS(0.909) values demonstrate a high accord between observed and predicted water depths. Molinate concentrations in ponded water had an RMSE of 0.036mg/L, and the REE was 0.061mg/L.
2. The calibrated model was used in scenario analysis to understand the potential effect of the predicted molinate concentrations with different water depths and various pesticide management practices(amount and treatment method). The scenarios were run between 4 June and 2 September for 1997-2006, using the same parameter values as those that were used for the initial calibration.
3. Based on the water management scenario analysis, it was concluded that the very shallow irrigation method could ensure a sustainable water resource and also had the benefit of protecting aquatic ecosystems from pesticide exposure. On the other hand, very shallow irrigation must be carefully attended for the first 5 DATs, as during this time the molinate concentration is very high.
4. Based on the pesticide treatment amount scenario analysis, the withholding periods for a molinate treatment of double the label rate in rice paddies with deep, shallow and very shallow conditions is recommended, over the 37.0, 34.0 and 31.0 DATs, respectively. These results of the pesticide treatment amount scenario analysis show that using the application rate specified on the label will provide the most effective and economic pest management.
5. Based on the pesticide treatment amount scenario analysis, the withholding periods for a molinate treated by power granule sprayer under the deep, shallow and very shallow irrigation conditions were evident after 33.0, 28.6 and 25.4 DATs, respectively. Therefore, it is recommended that the withholding period for these conditions, to prevent the adverse ecological effects on populations, should be more than 26.0 DATs. Recently, granule formulations including molinate have been used widely to control pests. However, the existing sprayer was developed for wettable and dustable powder, not for granules. If an improved sprayer were developed that could prevent to drift in the air, the utilization of this sprayer could save labour, time and money, and decrease the risks associated with granular pesticide.
6. The most important element in BMPs for aquatic ecosystem conservation is the use of the withholding period in rice paddies. The withholding period in the case of molinate used in rice paddies has been about 3 to 4 DATs, as recommended by the pesticide label in Korea. In the results of this study, for adjacent aquatic organism conservation, the withholding period must be more than 26.0 DATs.