METAMITRON AND CHLORIDAZON DISSIPATION IN A SILTY CLAY LOAM SOIL

The dissipation of chloridazon in a silty clay loam soil under laborat ory and field conditions was similar to that of metamitron, and they w ere both affected by temperature and soil moisture. The t(1/2) of chlo ridazon, at 22% soil moisture, decreased from 76 to 14 days with tempe rature increase from 10 to 30 degrees C; the t(1/2) Of metamitron, in the same conditions, decreased from 40 to 7.5 days. At 10 degrees C th e effects of an increase in soil moisture from 15 to 29% were larger o n chloridazon degradation, with t(1/2) decreasing from 134 to 41 days; the t(1/2) of metamitron decreased from 46 to 21 days. DT50 values me asured in the topsoil (0-5 cm) were slightly different, 68 and 51 days , for chloridazon and metamitron, respectively, and no residues were d etected in soil/water solutions at 20 cm depth 3 months after applicat ion. These results show that in Italian conditions during the first 80 days after herbicide application and in the absence of rainfall the s oil persistence of the herbicides is high and the mobility in soil is low.