ALACHLOR DISSIPATION IN SOIL AS INFLUENCED BY FORMULATION AND SOIL-MOISTURE

The persistence of alachlor applied as pure active ingredient (ALA), emulsifiable concentrate formulation (Lasso EC), and two microencapsulated formulations (Lasso ME and Chloral ME) in a clay loam soil was examined under laboratory standard conditions at 25-degrees-C, at various moisture levels. The order of persistence of alachlor was as follows: Lasso ME > Chloral ME > Lasso EC > ALA at 50 and 75% of field moisture capacity (FMC) and Lasso ME > Lasso EC > Chloral ME > ALA at 25% of FMC. The half-life of ALA increased from 5 to 13 days with decreasing moisture percent. The rates of degradation of Lasso EC were about the same at 50 and 75% of FMC (t1/2 = 10 and 9 days), whereas it was much lower at 25% of FMC (t1/2 = 38 days). In contrast, both microencapsulated formulations were more persistent at high moisture levels (t1/2 > 56 days), while at 25% of FMC the half-life was 49 days for Lasso ME and 34 days for Choral ME. Field experiments on the persistence of Lasso ME indicated that alachlor concentration was <25% of the initial dose 18 days after application. No alachlor was detectable below a 10-cm depth. Alachlor was detected in soil solution and gravitational water up to a 60-cm depth but at very low concentrations (1.13 and 0.22-mu-g/L).