Persistence of atrazine as affected by selected soil properties

The relationships between selected soil properties and the bioactivity of atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) were investigated in field trials. Bioactivity was determined periodically for up to twelve months on a variety of soil types using oats (Avena sativa L.) as the test plant. The initial bioactivity of atrazine which was assessed 35 days after application was best correlated with the organic matter content (%C) and P reversion characteristics of the soils. Clay content and CEC were also important but at lower levels of significance. Six months after herbicide application, % C, soil pH and P reversion were important predictors of atrazine persistence, whilst both CEC and clay content were poor criteria. Persistence was negatively correlated with % C, but positively with both soil pH and P reversion. Since the dissipation of atrazine in most of the soils was virtually complete after twelve months, the prediction of persistence by the soil properties was poor at that stage. Differences in persistence between trials in close proximity suggest that persistence of the herbicide was more closely linked to soil characteristics than to climatic conditions. Results suggest that current waiting periods, which are recommended for specific crops, can be refined by distinguishing between soils on the basis of soil characteristics that affect adsorption and degradation of atrazine.