APPLICATION METHOD - IMPACTS ON ATRAZINE AND ALACHLOR MOVEMENT, WEED-CONTROL, AND CORN YIELD IN 3 TILLAGE SYSTEMS

Banding herbicides reduces the agrochemical input compared to broadcas t applications, and thereby reduces negative environmental impacts of herbicides. This study evaluated the impact of three tillage systems ( ridge tillage, chisel plow, and moldboard plow) and two preemergence h erbicide application methods (band and broadcast) on atrazine and alac hlor movement, weed control, and corn (Zea mays L.) yield on two soils , one with a loam and the other with a silty clay loam texture in the surface layer. A 25 cm or 38 cm herbicide band applied over a 76 cm co rn row compared to broadcast application reduced herbicide input by 67 -50%, respectively. Shallow cultivation was used for weed control betw een rows in all tillage systems. Tillage system did not impact herbici de movement, weed control, or corn yield. Although less than 1% of the applied herbicide was detected in soil below 45 cm, atrazine and alac hlor were found in water samples collected from pan lysimeters buried 90 cm below the surface. Banding reduced atrazine and alachlor collect ed in lysimeters by 50% and 80%, respectively, compared to a broadcast application for continuous corn; in finer textured soil. However, eve n in the banded application, atrazine levels in some years increased f rom <0.1 (background) to a maximum of 0.8 mu g l(-1) in a shallow aqui fer 5.5 m below the surface of the silty clay loam soil when managed a s a soybean [Glycine max (L.) Merr.] - corn rotation using the ridge t illage system. Yellow foxtail (Setaria glauca (L.) Beauv.) was the mos t abundant weed in the loam soil where corn yield was similar in band and broadcast treatments because cultivation could be and was timely a fter rainfall. In the silty clay loam soil, corn yields were less in b anded than broadcast treatments in one out of the three years. Yield r eductions in the banded treatment on this silty clay loam soil were at tributed to poor control of Russian thistle (Salsola iberica Sennen an d Pau), redroot pigweed (Amaranthus retroflexus L.), ladysthumb (Polyg onum persicaria L.), and yellow foxtail because cultivation could not be done timely after rainfall. (C) 1998 Elsevier Science B.V. All righ ts reserved.