Recent studies in Arkansas have demonstrated the potential of wheat-soybean relay intercropping as an effective strategy for mitigating weed pressure in soybean systems. Preliminary findings suggest that this system not only enhances weed suppression but also may improve system-wide productivity and profitability. However, variability in environmental conditions across agroecological zones presents a challenge for broader adoption. Further research is necessary to assess the scalability and effectiveness of wheat-soybean relay intercropping across diverse regions and weed species.

Herbicides and associated technologies remain indispensable tools in modern agriculture. However, the prolonged reliance on herbicide-centric weed management approaches has inadvertently accelerated the evolution of herbicide-resistant weed populations, creating a critical need for non-chemical alternatives to sustain long-term weed control. Species like Palmer amaranth, an aggressive and resilient weed, threaten to overwhelm conventional management practices and could significantly reduce crop yields if left unchecked. The stagnation in the development of novel herbicide modes of action has resulted in a precarious scenario where the evolution of herbicide resistance has outpaced chemical innovation (Duke 2012; Heap 2024).

While existing herbicides remain effective in many regions, the evolutionary adaptability of weeds underscores the urgent need to diversify weed management strategies. This urgency has long been recognized by experts (Baker 1974; Buhler 2002; Norsworthy et al. 2012) and remains a prominent topic in current agricultural discourse (Bagavathiannan and Davis 2018). Unfortunately, non-chemical weed control methods that complement conventional systems remain underdeveloped and underutilized.

Wheat-soybean relay intercropping offers a potential solution by reducing the dependency on chemical herbicides while simultaneously delivering economic benefits and minimizing environmental impacts. Research has shown that wheat used as a cover crop can significantly reduce weed establishment, creating a protective window before soybean canopy closure (Osipitan et al. 2019). Recent studies in Arkansas have identified wheat-soybean relay intercropping as a promising tool for managing Palmer amaranth. The system effectively reduces the selection pressure exerted on weed populations by herbicides, which is essential for sustainable weed management. In addition to its weed control benefits, relay intercropping may improve economic returns compared to conventional full-season soybean systems and is comparable to the less common wheat-soybean double-crop systems. However, further research is necessary to evaluate its effectiveness across various growing conditions and weed species. Expanding our understanding of how this intercropping system interacts with diverse environmental factors in terms of weed control and system productivity is crucial for its broader adoption.

The outcomes of this research will provide valuable information to growers, agronomists, and policymakers about the relay intercropping and its potential benefits. This multi-regional project aims to offer a scalable solution to the challenges posed by herbicide-resistant weeds, supporting growers in affected regions and promoting proactive, sustainably profitable agricultural practices.

The overall goal of this research is to expand the geographic scope, understand regional producer perspectives, and address the knowledge gap regarding weed suppression and crop yield in both full-season and wheat-soybean relay intercrop systems.
Objective #1. Evaluate and compare the weed management outcomes under similar or nearly equivalent herbicide regimes between full-season and wheat-soybean relay intercropping systems.
Objective #2. Assess the impact of residual wheat herbicide application on early-season weed suppression in intercropped soybean.
Objective #3. Understand the feasibility of a wheat-soybean relay intercropping system across a wide geography under a range of environmental conditions.
Objective #4. Evaluate and summarize regional producers’ familiarity, interest, implementation barriers, and perceived risk related to wheat-soybean relay intercrop systems.

This project builds upon encouraging preliminary results and aims to further evaluate the effectiveness of wheat-soybean relay intercropping. The evaluation of this project will rely on both agronomic and economic metrics, with the following Key Performance Indicators (KPIs):
1) Weed Management Outcomes: Quantitative assessments of weed density will be conducted at regular intervals throughout the growing season. Data will be collected for both the relay intercropping and full-season soybean systems to allow for a comparative analysis.
2) Agronomic Performance: Yield measurements for both wheat and soybean will be recorded. Comparisons will be made between the relay intercropping system and the traditional full-season soybean system to assess productivity under each management approach.
3) Survey Metrics: Completion rate and regional representation of respondents will be documented.
4) Economic Justification: An economic analysis will be conducted, considering the input costs associated with each system (herbicides, labor, machinery, etc.) as well as revenue generated from crop yields.

These performance measures will be tracked across all site-years, and the findings will inform broader recommendations for improving weed management practices and overall system sustainability in soybean production.

Updated July 23, 2025:
Title: Evaluating Wheat-Soybean Relay Intercropping for Improved Weed Management Outcome and System Yield
Principal Investigator: Jason K. Norsworthy

Field activities for the wheat–soybean relay intercropping project were implemented across multiple states by a total of six collaborators for the 2024–2025 growing season. Collaborators in Arkansas, southern Illinois, Indiana, and Kansas shared protocols focused on herbicide treatments applied either in wheat during the fall or in early-season soybean. Other collaborators in Indiana and Kansas also established both full-season and relay intercropping systems under conventional weed management practices.
Wheat was planted in fall 2024 at the normal planting time for the region at most locations. In Iowa, planting was delayed due to late wheat seed delivery, which impacted stand establishment and led to early termination at two sites. Nevertheless, wheat stands at the remaining three sites in Iowa were sufficient to proceed with relay soybean planting. Across all sites, soybeans were interseeded into standing wheat in April or May 2025, depending on local conditions. Full-season soybeans were planted either at the time of interseeding or at the regionally appropriate planting time, depending on the specific objectives of each study.

Poor wheat establishment and soybean outgrowth posed challenges for wheat harvest at some sites. In Iowa, weak fall growth resulted in shorter-than-expected wheat, which created harvestability issues within the relay system, particularly since this was the first year these farmers used wheat instead of cereal rye. In Kansas, excess rainfall around harvest caused soybean plants to outpace wheat growth, complicating harvest operations and prompting plot-level adjustments.

At all sites, herbicide applications have been completed, and early-season visual and quantitative assessments have been conducted. Early-season weed suppression from wheat has been notable, with several sites reporting reduced pressure from species such as broadleaf signalgrass, Palmer amaranth, waterhemp, or johnsongrass in the relay intercropping system—consistent with expectations for this approach.

Overall, the field project remains on track across all sites. Collaborators are actively collecting in-season weed data, and end-of-season weed assessments and soybean yield measurements will be conducted at harvest.

Additionally, as part of this project, a multi-state survey led by collaborators from Kansas State University and Purdue University was launched on July 4, 2025. Targeting soybean producers and agronomists across thirty-five states, the survey has been disseminated through regional directors and Qualified State Soybean Boards (QSSBs). Broadly, it explores current production practices, awareness of intensification systems such as relay intercropping, and the potential for broader adoption. The survey will remain open throughout the summer and is being actively promoted through newsletters, social media, and university extension networks.

The outcomes of this research will provide valuable information to growers, agronomists, and policymakers about the relay intercropping and its potential benefits. This multi-regional project aims to offer a scalable solution to the challenges posed by herbicide-resistant weeds, supporting growers in affected regions and promoting proactive, sustainably profitable agricultural practices.