INFLUENCE OF HERBICIDE APPLICATION TIMING ON CORN PRODUCTION IN A HAIRY VETCH COVER CROP

The time of killing a hairy vetch (Vicia villosa Roth) cover crop rela tive to planting no-tillage corn (Zee mays L.) is critical to optimizi ng the benefits derived from the cover crop mulch. Research was conduc ted to determine the optimum timing for herbicide application to contr ol hairy vetch for no-tillage corn production. Herbicides were applied 1 to 3 wk before planting corn (preplant), immediately after planting corn (preemergence), or after corn emergence (postemergence). Herbici de plots were split by N sidedressing at 0 or 80 lb/acre. Biomass of h airy vetch increased by an average of 1620 lb/acre and N content incre ased by an average of 44 lb/acre between the preplant and preemergence application dates but little change occurred between the preemergence and postemergence application dates. Despite this N increase between herbicide applications, herbicide application date had no effect on co rn response to sidedressed N, Soil texture did appear to influence cor n response to sidedressed N; corn yield was higher when N was sidedres sed in two experiments on coarse-textured soils but was not influenced by sidedressing in two experiments on fine-textured soils. Yield was higher when corn was grown with the preplant herbicide program than th e preemergence herbicide program in one of four experiments and higher when corn was grown with the preplant herbicide program than the post emergence herbicide program in three of four experiments. Results indi cate that optimum yield of corn grown in a hairy vetch cover crop requ ires killing vetch before planting but sidedressing with N may only be necessary on coarse-textured soils.