Abstract
Effects of soil properties and microorganisms on the degradation of the herbicide atrazine was studied using five Japanese (alluvial and volcanic ash soils) and two Thai soils (alluvial and calcareous soils). Among soil properties, soil pH showed the highest positive correlation to the half-life of atrazine in the soils (r=0.79). Differences in the atrazine degradation rates in the soils at the same pH suggested that effects of other soil properties were also involved. Comparison of the atrazine degradation rates in sterilized (autoclaved) and nonsterilized soils indicated that the contribution of chemical degradation to atrazine degradation was more than 80% in a pH range of 4 to 8. The long-term application of atrazine did not increase the degradation rates. Although the contribution of microbial degradation was less than 20% and distinct only after 20 days of incubation, the population of atrazine degraders was 105-106 cells/g soil even in soils virgin to atrazine. This suggested that the microbial degradation of atrazine was mainly determined not by the population of atrazine degraders, but by soil conditions they work under.
