Effect of percolation flow on herbicide loss from rice paddies

摘要

The fate and transport of pretilachlor, one of the most widely used rice-paddy herbicides in Japan, were monitored in a rice paddy plot for 28 days after its application in the five study years. The effect of the percolation rate on herbicide loss was investigated. The concentration of pretilachlor in the paddy water was at its highest level within 2 days of application. The maximum concentration in percolated water was lower, and it was reached 1 or 2 days later than that in the paddy water. Almost all the pretilachlor loss was caused by percolation. The pretilachlor loss, as estimated from the amount that was applied and the cumulative percolation loss, ranged from 7.4 to 16.3%. In the five study years, the average percolation rate for the 7 days following application ranged from 11.5 to 29.3 mm/day. The pretilachlor loss increased proportionally with the percolation rate for 7 days following application.