Abstract
In model plots of turf and bare soil grounds with a 15 degree inclination, simulated rainfall of 80 mm was applied for 60 minutes at 6, 24 and 72 hours after application of herbicides (simazine, pendimethalin and asu-lam ), and runoff water and soil sediments including herbicides were collected. A significant soil erosion occurred in the bare ground plots, while no erosion was observed for the turfgrass plots. The amount of surface runoff water was higher in the bare ground plots than in the turfgrass plots where it greatly reduced when the mowing height was increased from 2 cm to 5 cm. In the bare ground plots, simazine was washed out with both soil sediments and runoff water, whereas pendimethalin was moved mainly with soil sediments. In contrast, larger amount of asulam was found in runoff water than in soil sediments. In all the turfgrass plots, the extent of herbicide runoff was less than in the bare ground plots, being least in the plots of 5 cm mowing height. The amount of the herbicides in runoff was high when the simulated rainfall applied shortly after application and then it declined with time.
In the turf and bare soil ground plots with a 33 degree inclination, simazine, commercially formulated as flowable or as wettable-powder, was applied at spray volume of 200 L /10a or 400 L/10a, and the herbicide runoff after simulated rainfall of 40 mm /h was examined. The total amount of simazine in the runoff water and in the soil sediments was affected significantly neither by spray volume nor by formulation types.
