The influence of magnesium on the toxicity of atrazine Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/jq085n30m

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  • Atrazine is an asymmetrical s-triazine herbicide used pre- and post emergence for weed control in many crops. Triazine herbicides have been used in the Pacific-Northwest for weed control in orchard crops. Under certain conditions where trees were grown in nutrient deficient areas, it was noted that toxic symptoms due to the herbicide appeared on the leaves of the trees. It was also noted that these symptoms were apparently overcome by the addition of foliar sprays containing the nutrient which was deficient in that area. This study was conducted to determine whether nutrients might have a significant effect in reducing the toxicity of herbicides. Magnesium and atrazine were chosen to study this interaction since it was known that both affected the photosynthetic processes of the plant. Plants were grown in sand cultures to avoid the complex interactions which occur between soils and herbicides. Nutrient solutions were used to provide a nutrient supply to plants grown in sand. Three different nutrient solutions were used containing zero-magnesium, medium-magnesium, and high-magnesium levels. These three nutrient solutions contained the same amount of all the other essential elements. Tomato plants were grown in sand cultures under three magnesium levels. Three weeks after planting, atrazine rates of 0, 1/16, 1/8, and 1/4 ppm were added to pots containing the plants. Plants were harvested six weeks after planting. Results of the experiment showed a significant growth increase due to the addition of magnesium. The statistical analysis also showed that the addition of magnesium helped overcome the toxicity of atrazine. A similar experiment using oat plants was carried out. Two weeks after planting, atrazine treatments of 0, 1/32, 1/16, and 1/8 ppm were added to the plants. Plants harvested five weeks after planting showed that the magnesium treatment had no significant effect on the dry weight of the oat plants. The interaction between magnesium and atrazine was also insignificant. The difference between the results of this experiment and the experiment involving tomatoes was probably due to seed size and the duration of the experiment. Small-seeded plants grown over a longer period of time allowed the magnesium and atrazine effects to appear. Tomato plant material from the magnesium-atrazine interaction experiment was used in the laboratory to determine the effects of magnesium and atrazine on the uptake of other plant nutrients. Results showed that atrazine had a significant effect in reducing the uptake of the thirteen nutrient elements analyzed. Ambient magnesium concentrations significantly influenced the uptake of magnesium and molybdenum. Preliminary research was conducted to determine the nutrient-supplying capability of the sand used in the experiment. Results from the laboratory showed that the macro-nutrient supply of this sand was extremely low. Plants growing in this sand would have to obtain their nutrients from an external source.
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