LEACHING OF ALACHLOR FROM ALGINATE-ENCAPSULATED CONTROLLED-RELEASE FORMULATIONS

The mobility of alachlor from alginate-encapsulated controlled-release (CR) formulations was investigated in two contrasting soil profiles. Two CR formulations of alachlor were prepared with the following compo nents (1) base-sodium alginate + kaolin + 'Tween' 20(R) (1 + 10 + 0 . 5 by mass) and (2) base + 40 g kg(-1) linseed oil. These were compared to technical grade alachlor and to a commercial alachlor EC formulati on ('Lasso' 4EC). All herbicide treatments were labeled with [C-14]ala chlor and were applied to duplicate soil columns that were composed of a surface and a subsoil horizon. Each horizon was packed to a depth o f 12 . 5 cm, giving a total column length of 25 cm. The columns were l eached with 21 cm (420 ml) to 30 cm (600 ml) of 0 . 01 M calcium chlor ide for a period of 7 to 10 days. Alachlor leaching from the EC formul ations was the same as that from the technical material in both soils: 33% in the Evesboro and 10% in the Conover soil. The CR-Oil formulati on leached 4 and 2% of the applied [C-14]alachlor, compared to 12 and 3% for the CR-N formulation for the Evesboro and Conover soils, respec tively. The CR-Oil formulation also increased the amount of [C-14]alac hlor retained in the soil surface horizon (105-114%), compared to CR-N (39-45%), technical material (14-23%) and EC (12-17%).