EFFECTS OF ATRAZINE-MINERALIZING MICROORGANISMS ON WEED GROWTH IN ATRAZINE-TREATED SOILS

The herbicidal effect of atrazine on sensitive plant species was studi ed in soils inoculated with bacteria capable of mineralizing atrazine. Nasturtium officinale and Solanum nigrum plants died within 15 days a fter sowing in soil containing atrazine incorporated at 4 mg/kg. Norma l growth of N. officinale was obtained when 5 mg/kg atrazine-mineraliz ing bacteria was mixed into the soil containing atrazine, prior to see ding. Atrazine concentrations in soil declined by 90% within 5 days as a result of the atrazine degradation by the bacteria added to the soi l. Normal growth of S. nigrum plants was observed in soils receiving o nly 0.1 mg/kg atrazine-degrading bacteria. The efficacy of atrazine in the presence of atrazine-degrading bacteria was also tested on N. off icinale 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 herbici de breakdown was rapid and the effect of the herbicide on the indicato r plants was drastically diminished when the soil was kept under condi tions favorable for the atrazine-degrading bacteria.