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 relative to planting no- tillage corn (Zea mays L.) is critical to optimizing the benefits derived from the cover crop mulch. Research was conducted to determine the optimum timing for herbicide application to control hairy vetch for notillage corn production. Herbicides were applied 1 to 3 wk before planting corn (preplant), immediately after planting corn (preemergence), or after corn emergence (postemergence). Herbicide plots were split by N sidedressing at 0 or 80 lb/acre. Biomass of hairy vetch increased by an average of 1620 lb/acre and N content increased 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 corn response to sidedressed N. Soil texture did appear to influence corn response to sidedressed N; corn yield was higher when N was sidedressed 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 the preemergence herbicide program in one of four experiments and higher when corn was grown with the preplant herbicide program than the postemergence herbicide program in three of four experiments. Results indicate that optimum yield of corn grown in a hairy vetch cover crop requires killing vetch before planting but sidedressing with N may only be necessary on coarse-textured soils. Research QuestionHairy vetch is a winter annual legume that can improve soil tilth, provide N for subsequent crop growth, and suppress weeds. The time of killing hairy vetch relative to planting no-tillage corn can influence the benefits derived from the cover crop mulch. This research was conducted to determine the optimum timing for herbicide application in large-scale plots on production fields at Beltsville, MD. Background InformationMaintaining a live hairy vetch cover crop for as long as possible after corn planting could improve weed suppression and potentially reduce herbicide requirements. Consequently, a postemergence-only herbicide program in which herbicides were applied only if vetch became too aggressive or if weeds emerged may be well-suited for corn planted into live hairy vetch. This system could reduce reliance on residual herbicides and rely, instead, on the potential of relay planting to deny weeds their usual niche immediately after planting. This approach also could permit maximum production of vetch biomass and N and may better synchronize N release with corn demand. The objectives of this research were to contrast a total postemergence system for managing corn production in a hairy vetch cover crop with a conventional preplant or preemergence system and to determine whether sufficient vetch N was produced in the total postemergence system to eliminate the need for fertilizer N. Study DescriptionTreatment comparisons were made on large plots traversing production fields during normal no-tillage corn production at the Beltsville Agricultural Research Center. Herbicides were applied 1 to 3 wk before planting corn (preplant), immediately after planting corn (preemergence), or after corn emergence (postemergence). Herbicide plots were split by N sidedressing at 0 or 80 lb/acre. Applied QuestionsDid delaying hairy vetch kill date increase vetch biomass and N production? Delaying hairy vetch kill until corn planting resulted in an average increase of 1620 lb/acre in vetch biomass and 44 lb/acre of N compared with the preplant kill date. The rapid vetch growth during this 1 to 3 wk period in mid-May resulted in biomass levels at corn planting ranging from 3200 to 5930 lb/acre and N production of 110 to 190 lb/acre. Delaying hairy vetch kill until postemergence resulted in little or no additional vetch biomass accumulation over that present at corn planting. The coulters and tires of the planter killed approximately half of the vetch during the planting operation and reduced the vigor of the surviving vetch. Did the postemergence-only herbicide program control weeds? Weed control in 2 of 4 experiments was poorer in the postemergence-only program compared with the preplant or preemergence programs. The cover crop mulch did not provide full-season weed control but required a postemergence herbicide application. Reliance on a postemergence-only herbicide program, however, proved risky because weather interfered with timely applications and the absence of residual herbicides permitted development of late-emerging weeds. Did herbicide program influence corn yield? Yield of corn treated with the preplant herbicide program was higher than the yield of corn treated with the preemergence herbicide program in one of four experiments and was higher than the yield of corn treated with the postemergence herbicide program in three of four experiments. Yield loss associated with vetch killed later than planting could be attributed to reduced corn stand, increased insect pressure, greater moisture removal by the vetch cover crop, or inconsistent weed control. Optimum yield of corn grown in a hairy vetch cover crop, therefore, required killing vetch 1 to 3 wk before planting and controlling weeds with a suitable herbicide program. Did sidedressed N influence corn yield? The response of corn to sidedressed N was not influenced by herbicide program despite the higher N available with later herbicide application dates. Sidedressed N increased corn yield in two experiments on coarse-textured soils but not in two experiments on fine-textured soils. These results indicate that the need for sidedressed N may be limited to corn grown on coarse-textured soils. More research is needed to determine the influence of soil texture on N management of corn grown in a hairy vetch mulch.