Effects of Atrazine-Mineralizing Microorganisms on Weed Growth in Atrazine-Treated Soils

Abstract

The herbicidal effect of atrazine on sensitive plant species was studied in soils inoculated with bacteria capable of mineralizing atrazine. Nasturtium officinale and Solanum nigrum plants died within 15 days after sowing in soil containing atrazine incorporated at 4 mg/kg. Normal growth of N. officinale was obtained when 5 mg/kg atrazine-mineralizing bacteria was mixed into the soil containing atrazine, prior to seeding. Atrazine concentrations in soil declined by 90% within 5 days as a result of the atrazine degradation by the bacteria added to the soil. Normal growth of S. nigrum plants was observed in soils receiving only 0.1 mg/kg atrazine-degrading bacteria. The efficacy of atrazine in the presence of atrazine-degrading bacteria was also tested on N. officinale and Agrostis tenuis in greenhouse trials under simulated field conditions using a commercial atrazine formulation and the herbicide sprayed onto soil in open containers. Here, too, the microbial herbicide breakdown was rapid and the effect of the herbicide on the indicator plants was drastically diminished when the soil was kept under conditions favorable for the atrazine-degrading bacteria.