Atrazine availability and persistance in Manitoba soils

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Thompson, Gordon Ian.
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The amount of atrazine breakdown over time and the efficacy of atrazine in three Manitoba soil types were investigated. Growth chamber bioassay experiments using oats (Avena sativa L. var. Harmon) were conducted over an eighteen month period using soil from the three locations. Herbicidal activity of atrazine was found to be most pronounced in the sandy and low organic matter soils. Soil texture, organic matter and cation exchange are the predominant factors affecting atrazine activity. A field bioassay was conducted in the fall of 1973 and the spring of 1974 to investigate the change in atrazine activity under field conditions over time. The field bioassay indicated atrazine activity was greater in the sandy and low organic matter soils. Spring seeded bioassays showed more atrazine activity than the fall seeded bioassay. An analytical analysis of atrazine residues was made of all the field plots. It was found that breakdown occurred more rapidly in the sandy loam soil, but there was very little difference in the rate of breakdown between the clay loam and clay soils. Atrazine appeared to be a persistent herbicide in Manitoba soils and under uncultivated soil conditions atrazine could cause damage to succeeding susceptible crops in most Manitoba soils.