Comparison of the persistence of atrazine and metolachlor under field and laboratory conditions

A study was carried out in a loamy soil to evaluate the degradation of atra zine and metolachlor under laboratory-controlled and field-variable conditi ons as a function of temperature and soil moisture content. In laboratory t rials, metolachlor showed fast degradation, with half-lives from 100 to 5.7 days in a temperature range from 5 to 35 degrees C at 100% of field capaci ty, whereas in the same conditions the degradation rate of atrazine was rel atively slow, with half-lives from 407 to 23 days. Modeling of laboratory d egradation data to predict field persistence was carried out. Field persist ence of atrazine and metolachlor was measured in the same soil during the c orn growing seasons in 1993, 1994, and 1996. In the three years the mean ha lf-dissipation times for atrazine and metolachlor were 36 and 21 days, resp ectively. Calculations from model equations gave acceptable prediction of f ield dissipation of both herbicides. Limitations and perspectives of employ ed modelization procedure are discussed.