Leaching of Alachlor from Alginate-Encapsulated Controlled-Release Formulations

Abstract

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 components (1) base-sodium alginate + kaolin + 'Tween' 20® (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 formulation ('Lasso' 4EC). All herbicide treatments were labeled with [ 14 C]alachlor and were applied to duplicate soil columns that were composed of a surface and a subsoil horizon. Each horizon was packed to a depth of 12.5 cm, giving a total column length of 25 cm. The columns were leached with 21 cm (420 ml) to 30 cm (600 ml) of 0.01 M calcium chloride for a period of 7 to 10 days. Alachlor leaching from the EC formulations 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 formulation leached 4 and 2% of the applied [ 14 C]alachlor, compared to 12 and 3% for the CR-N formulation for the Evesboro and Conover soils, respectively. The CR-Oil formulation also increased the amount of [ 14 C]alachlor retained in the soil surface horizon (105-114%), compared to CR-N (39-45%), technical material (14-23%) and EC (12-17%).