“…Residues of triazine herbicides such as atrazine (2-chIoro-4-ethylamino-6-isopropyiamino-1,3,5-triazine) and simazine (2-chloro-4,6-bisethylamino-l,3, 5-triazine), and urea herbicides such as linuron (7V'-(3,4-dichlorophenyl)-A^-methoxy-A'-methylurea) and diuron {A'"'-(3,4-dichl or phenyl)-A'^A'-di methylurea) can persist in the soil in amounts sufficient to damage sensitive crops the following year (Frank, 1966;Burnside et al, 1969;Upchurch, Corbin & Selman, 1969;Morris & Penney, 1971) and methods of detecting phytotoxic concentrations of these compounds prior to the planting of susceptible crops are often required. The amount of residues of these herbicides in soil is commonly determined by bioassay methods where the growth of plants of a susceptible species in soil containing an unknown amount of herbicide is compared to the growth in soil treated with known amounts of herbicide.…”