PERSISTENCE AND MOVEMENT OF ATRAZINE, BROMACIL, MONURON, AND SIMAZINE IN INTERMITTENTLY-FILLED IRRIGATION DITCHES

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Abstract
Atrazine (22.4 kg/ha), bromacil (15.2 kg/ha), monuron (35.8 kg/ha), and simazine (22.4 kg/ha) were applied to especially prepared irrigation ditches in the fall of 1970. Soil samples from ditch sides, ditch bottoms, and basins irrigated with water were taken during 1971, 1972, and 1973 seasons. Water samples were also taken during these years. The soil and water samples were analyzed chemically to determine the herbicide residues remaining in the ditches and basins, their movement in the soil profile, and the amount of herbicides carried in the flowing water over the 3-yr period. The order of persistence for the four herbicides was simazine > atrazine > monuron > bromacil. Atrazine, bromacil and monuron residues were distributed uniformly throughout the 90-cm soil depth by the third growing season. The greater part of simazine residues was, however, still present in the top 7.5-cm soil layer. In irrigation waters, the highest herbicide concentrations were in the initial ponding in the spring of 1971, decreasing by a factor of two- to fivefold in the second filling in 1971. The relative amounts of each herbicide in the first two water samplings were inversely proportional to their respective water solubilities.

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