ATRAZINE AND ALACHLOR CONCENTRATIONS UNDER RIDGE-TILLAGE AND CHISEL-PLOW TILLAGE IN AN ALLUVIAL PLAIN SOIL

Although agricultural fertilizers and herbicides have significantly im proved crop yields during the past 30 years, there is concern regardin g the presence of these chemicals within certain environments. Atrazin e and alachlor presence in an alluvial plain soil in south-central Ohi o, USA, was evaluated over a 5-year period under ridge- and chisel-plo w-tillage systems. The ridge-tillage plots included one large held-sca le plot, 10 ha in size, and nine 0.4 ha plots used for replicating eac h phase of the corn (Zea mays L.)-soybean (Glycine max L.)-wheat (Trit icum aestivuum L.) rotation every year; three plots for corn, three pl ots for soybean, and three plots for wheat. The chisel plowed plots wi th continuous corn included one large field-scale plot, 10 ha in size, and three 0.4 ha plots used for replicated studies. Soil cores were t aken from all plots, approximately biweekly during the growing season and monthly during the non-growing season, from under the row for the period from 1991 to 1993. Soil cores were taken approximately monthly during the growing season from under the row and between the rows in 1 994 and 1995. Measured concentrations of atrazine and alachlor were si milar in soil samples taken from under the row in the chisel-plowed, c ontinuous-corn and ridge-tilled, corn-soybean-wheat systems. Atrazine and alachlor concentrations measured under the row, and between the ro w, were generally significantly different (42 of 54 sampling events) i n the ridge-tillage system because a banded application of herbicides was used. Movement of herbicides from the ridge position to the valley position was not evident. Herbicide usage was reduced by 66% because of the banding operation in the ridge-tillage cropping system. A simil ar reduction in herbicide usage could occur in the chisel-plow system if herbicides were applied in a band and cultivation was used to contr ol weed pressure between the rows. Chisel-plow tillage with a banded a pplication of herbicides may be a favorable alternative for farm opera tors wishing to reduce herbicide usage without converting to the contr olled traffic, ridge-tillage system. (C) 1998 Elsevier Science B.V. Al l rights reserved.