INTERACTIONS OF TILLAGE AND RAINFALL ON ATRAZINE LEACHING UNDER FIELDAND LABORATORY CONDITIONS

Laboratory studies were conducted to evaluate effects of tillage rever sal and rainfall on C-14-atrazine 2-chloro-4-ethylamino-6-isopropylami no-s-triazine) leaching patterns. Twelve intact soil cores (16 cm dia x 20 cm deep) were collected from 8-yr no-till (NT) fields. Half the c ores were tilled (5 cm deep) prior to C-14-atrazine treatment (2.7 mg core(-1)) to all cores. All cores received two rains (27 mm rain in 1. 5 h, one day after application followed, two days later, by a 17 mm ra in in 2.5 h) and leachate was collected and analyzed for atrazine. The se rains simulated the timing, amount and duration of natural rainfall events from a tillage reversal field study. During the first high int ensity rainfall event, a pulse (2.1 mu g L-1) of atrazine leached thro ugh tilled cores while leaching rate was linear and decreased (1.25 to 0.9 mu g L-1) through un-tilled cores. Leaching rate was linear for b oth the tilled and un-tilled cores during the second rain. Less atrazi ne was left in the surface 5 cm of tilled soil than un-tilled after th e two rains. Results confirmed field observations and suggested that w hen tillage is reversed on well structured soils, pesticide leaching m ay increase relative to un-tilled soil but these effects are probably confuted to the first rain events after application only. (C) 1997 Els evier Science Ltd.