MOBILITY AND PERSISTENCE OF ALACHLOR, ATRAZINE AND METOLACHLOR IN PLAINFIELD SAND, AND ATRAZINE AND ISAZOFOS IN HONEYWOOD SILT LOAM, USING FIELD LYSIMETERS

Abstract

Mobility and persistence of commercial formulations of alachlor, metolachlor and isazofos were studied under two moisture regimes using 75 × 15 cm field lysimeters. Formulated atrazine was also applied to each lysimeter for reference purposes. Alachlor- and metolachlor-treated lysimeters were packed with Plainfield sand, while Honeywood silt loam was used to pack isazofos-treated lysimeters. Effluent was monitored for each chemical, and selected cores were sectioned (7 × 10 cm) and analyzed to determine mobility profiles and persistence at weeks 1, 2, 4, 8, 12 and 21. The 50% disappearance times (DT50) for alachlor, atrazine, isazofos and metolachlor were: <1.5, 4, 1.5 and 3 to 4 weeks, respectively. Water application during week 1, following pesticide application, created ponding on Honeywood soil cores, transporting atrazine and isazofos to a maximum 50-cm depth. While isazofos moved no further after week 1, atrazine and desethylatrazine (Des-Atr.) exhibited considerable mobility throughout the study. Ponding on Honeywood silt loam cores produced greater atrazine and Des-Atr. movement than in Plainfield sand cores. Des-Atr. production increased with soil moisture content. Relative mobilities in Plainfield sand were: Des-Atr. ≥ atrazine > metolachlor > alachlor; in Honeywood silt loam: Des-Atr. > atrazine > isazofos.