Integrating Hairy Vetch Cover Crop to Suppress Palmer amaranth and Enhance Nitrogen Availability for Popcorn Production in the North Central Region

Commodities

Practices

Popcorn production in the North Central Region-including Nebraska, Indiana, Illinois, Ohio, and Missouri-is valued at approximately $240 million annually. Nebraska leads the U.S. popcorn production, contributing about 35% of the national supply, with an estimated annual value of $66-$81 million. Despite its economic importance, popcorn production faces significant challenges. Surveys and discussions with growers consistently identify herbicide-resistant Palmer amaranth (Amaranthus palmeri S. Watson) and nitrogen (N) management as the most critical constraints, threatening long-term profitability and sustainability of popcorn production in the North Central Region.

The widespread occurrence of herbicide-resistant Palmer amaranth underscores the need for diversified, integrated management strategies that reduce reliance on herbicides. Hairy vetch (Vicia villosa Roth), a winter annual legume cover crop, may offer a solution. When planted in the fall and terminated after popcorn planting, hairy vetch can produce a dense mulch that suppresses early-season Palmer amaranth emergence. Additionally, as a legume cover crop, it fixes atmospheric N, which becomes available to the subsequent popcorn crop, potentially reducing synthetic fertilizer requirements while improving soil health.

This project will evaluate hairy vetch termination at multiple popcorn growth stages to determine the optimal balance among Palmer amaranth suppression, soil N availability, and popcorn grain yield. Soil N dynamics, including total N, nitrate, and ammonium, will be monitored throughout the growing season. Palmer amaranth emergence, density, biomass, and seed production will be quantified, along with popcorn growth, N uptake, and grain yield. Economic analysis will be conducted to determine the cost-benefit ratio of the treatments evaluated in this project.

Results will provide science-based recommendations for integrating hairy vetch cover crop into popcorn production systems as a scalable and economically viable strategy to manage herbicide-resistant Palmer amaranth, improve N management, and reduce fertilizer cost. On-farm research trials conducted with three cooperating growers, combined with targeted Extension activities, will facilitate adoption. Program evaluation, conducted in collaboration with the University of Nebraska-Lincoln's Bureau of Sociological Research ($3,416; see a letter of collaboration), will document project impacts. This multidisciplinary project aims to enhance profitability, reduce input reliance, and improve the long-term sustainability of popcorn production in the North Central Region.

The specific objectives of this project are to:

1. Evaluate hairy vetch termination timings to optimize Palmer amaranth suppression, N availability, and popcorn yield.
2. Quantify Palmer amaranth population dynamics, including emergence timing, biomass accumulation, density, and seed production under hairy vetch cover crop and herbicide management treatments.
3. Assess integration of hairy vetch with herbicide programs to enhance Palmer amaranth control in popcorn.
4. Evaluating the economic feasibility and cost-benefit ratio of treatments for integrated Palmer amaranth and N management in popcorn.

The first objective focuses on identifying termination strategies that maximize the agronomic and ecological benefits of hairy vetch. As a winter annual legume cover crop, hairy vetch contributes biologically fixed N, improves soil structure, enhances microbial activity, and produces substantial biomass capable of suppressing early-season weeds through mulch effects. However, termination timing strongly influences biomass accumulation, N mineralization patterns, soil moisture dynamics, and subsequent cash crop performance. Early termination may limit weed suppression and N contributions, while delayed termination may enhance mulch persistence but potentially interfere with planting operations or soil water availability. This project will evaluate multiple termination stages to determine optimal management windows that synchronize N release with popcorn demand while maximizing Palmer amaranth suppression and popcorn grain yield.

The second objective addresses short-term and long-term Palmer amaranth management outcomes by quantifying Palmer amaranth emergence, density, biomass, and seed production. Because Palmer amaranth can produce hundreds of thousands of seeds per female plant, reducing seed return to the soil seedbank is critical for sustainable management. Measuring emergence timing will clarify how effectively hairy vetch residue delays or suppresses initial flushes and will be compared with and without pre-emergence herbicide. Palmer amaranth biomass and density assessments will quantify competitive impacts on popcorn, while seed production measures will inform long-term population management implications. These data will provide a comprehensive evaluation of how hairy vetch cover crop-based popcorn production system influence both in-season Palmer amaranth suppression and future infestation risks.

The third objective examines integrated weed management strategies that combine non-chemical and chemical tools. While hairy vetch cover crop residues can significantly reduce early-season weed pressure, they may not provide complete season-long control under heavy infestations. Therefore, this project will evaluate the integration of hairy vetch mulch with reduced or strategically timed herbicide applications. The goal is to determine whether hairy vetch cover crop system allows for lower herbicide inputs while maintaining effective control.

The fourth objective evaluates economic analysis by comparing input costs, including hairy vetch cover crop establishment, termination, and herbicide programs, with popcorn grain yield outcomes to determine system profitability. This cost-benefit evaluation is critical for farmer decision-making and aligns directly with NC SARE's goal of advancing economically viable farming systems.

Learning Outcomes:

This project will improve farmer and stakeholder understanding of:

• The potential multifunctional benefits of hairy vetch, including N fixation, soil health improvement, and Palmer amaranth suppression.
• Nitrogen dynamics following hairy vetch cover crop termination and strategies to better synchronize N availability with popcorn crop demand.
• Integrated Palmer amaranth management approaches that reduce reliance on single-tactic herbicide program.
• The long-term implications of reducing Palmer amaranth seed production for sustainable seedbank management in popcorn. Educational outreach will include field demonstrations, extension presentations, and accessible summary materials to ensure results are directly transferable to producers across the North Central Region.

Action Outcomes:

The anticipated action outcomes include:

• Adoption of optimized hairy vetch termination practices by popcorn growers.
• Increased implementation of diversified Palmer amaranth management systems that integrate cover crops with reduced herbicide inputs in popcorn.
• Improved performance of cropping systems to reduce evolution of herbicide-resistant weeds and long-term sustainability of herbicides as a part of integrated weed management program.
• Enhanced stewardship through reduced chemical inputs and improved soil health.
• Increased farm profitability through improved N use efficiency and reduced long-term Palmer amaranth management costs.
• By addressing weed suppression, nutrient management, economic viability, and long-term sustainability simultaneously, this project aligns strongly with NCR-SARE priorities.
• The outcome of this project will promote farming systems that are economically profitable. The project seeks to provide practical, research-based recommendations that empower growers in the North Central Region.