Availability of atrazine to plants in different soils

The concentrations of atrazine in the shoots of wheat plants growing in 12 different soils were directly proportional to the soil solution concentrations of herbicide estimated from slurry adsorption measurements. There was a marked discrepancy between the total uptake of herbicide and the amount theoretically supplied by mass-flow in response to transpiration. This discrepancy was less when plants were grown in nutrient solutions. In an experiment with one soil only, the half-life of atrazine was 22 days and when the solution concentration in this soil was corrected for this change, a much closer prediction of atrazine uptake could be obtained. The ways in which interactions between adsorption, breakdown and transpiration rates may affect herbicide toxicity under field conditions are discussed.