Enhanced degradation of atrazine in soils that receive annual applications of atrazine has been reported in the literature; yet, no study has evaluated the time period required for the development of enhanced degradation of atrazine under field conditions. Thus, field and laboratory experiments were conducted to determine the time required to develop enhanced degradation of atrazine under two cropping systems: continuous corn receiving annual applications of atrazine, and a corn cotton rotation receiving an application of atrazine once every two years. The effect of cropping system on the mineralization and field dissipation of atrazine was investigated at Stoneville, MS, on a Dundee Silt Loam. For both cropping systems, cumulative mineralization of 14CO2 labeled atrazine increased 8-fold from 2000 (10%) to 2005 (80%). Field dissipation of atrazine followed first order kinetics, and calculated half-lives for atrazine combined over 2003 and 2005 data increased in the order of continuous corn (8d) = corn cotton rotation (9 d) < no atrazine history (16 d). These data indicate that enhanced degradation of atrazine can occur in less than five years. Moreover, a corn cotton rotation that receives an application of atrazine once every two years does not significantly retard the development of a microbial population capable of rapidly mineralizing atrazine.
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