This work is part of Hannah Massengill's 2023 Thesis. This study examined how cereal rye cover can influence agronomic dynamics in soybeans. The impact of termination timing on cereal rye biomass was evaluated across 4 North Carolina locations for 2 growing seasons. Termination times were 4 weeks before and at soybean planting. Biomass samples were collected to determine if delaying termination significantly impacted the biomass achieved by the cereal rye cover.

Previous literature suggests cereal rye biomass will increase with delayed termination (Mirsky et al., 2011; Wallace et al., 2017). Cover crop biomass has been shown to positively correlate with several benefits, such as weed suppression (Hodgkiss et al., 2020). However, terminating at or around the planting of a following cash crop may enhance several challenges, like proper planting and crop establishment (Mirsky et al., 2013; Clark et al., 2017). It also may increase pest pressure for the following crop (Lu et al., 2000; Bakker et al., 2016; Wallace et al., 2017; Wallander, 2021). These results can improve North Carolina growers' ability to assess the risks and rewards of delaying cereal rye termination closer to soybean planting.

• Edgecombe County
• Montgomery County
• Rowan County
• Washington County

Figure 1. County Location Map

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Figure 1. County Location Map

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Environments:

• 4 locations x 2 years = 8 total environments

Cereal Rye Seeding Rate:

• 80 lbs/acre

Termination Method:

• Chemical: Glyphosate

Termination Treatments (Table 1 & 2):

• 4 weeks before soybean planting (Burndown).

• Terminated at soybean planting (Green).

Biomass Measuring:

• Biomass collected at termination.

• Biomass dried 2 - 4 days at 65 C

Cereal rye biomass ranged from 1325.4 lbs/acre to 6006.5 lbs/acre across environments and treatments (Figure 2). Delaying termination (Green) resulted in significantly higher cereal rye biomass for only 3 of 8 environments (Figure 2). Montgomery 2021 (62% increase), Edgecombe 2022 (42% increase), and Washington 2022 (22% increase). The remaining 5 environments saw no significant gain in biomass from delaying termination an additional 4 weeks (Figure 2).

Figure 2. Effect of termination timing on biomass production across environments. Means of biomass values across eight environments with standard error bars. Letter groupings are specific to individual environments. Burndown indicates terminating cover crops four weeks before soybean planting. Green indicates terminating cover crops at soybean planting.

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Figure 2. Effect of termination timing on biomass production across environments. Means of biomass values across eight environments with standard error bars. Letter groupings are specific to individual environments. Burndown indicates terminating cover crops four weeks before soybean planting. Green indicates terminating cover crops at soybean planting.

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The wide range of biomass suggests factors outside management control can influence cereal rye growth and biomass. Planting dates and seeding rates were kept similar across the environments but did not produce uniform biomass across locations and years. Local site conditions and weather likely influenced the results. Growers must understand their regional and yearly context when determining biomass goals and assessing the success of a cover crop.

Delaying termination had no impact on biomass 62.5% of the time (Figure 2). In the 3 environments where delaying termination enhanced biomass, there was a significant temperature spike (10-11 degrees) during the 4 weeks between termination treatments. These results suggest that terminating cereal rye at soybean planting may not be necessary to maximize biomass in our Southeastern climate compared to regions with cooler temperatures like the Midwest.

Gains in cereal rye biomass are not linear throughout plant development and begin to plateau towards the later stages. NC State Extension Specialist Dr Reberg-Horton states, “These findings make sense for our environment. Cereal biomass peaks around heading time, and we usually have heading rye by mid to late April.”

The ability to reach heading sooner provides the flexibility to maximize biomass while avoiding risks associated with late termination, like the transfer of pests from the cover crop to the following cash crop. Entomology Extension Specialist Dr. Dominic Reisig recommends, “To minimize insect pest damage, try to time cover crop termination three to four weeks prior to soybean planting to minimize risk for pest spillover and unanticipated injury to the soybean crop.”

Dr. Rachel Vann, Soybean Extension Specialist, discussed the importance of interdisciplinary research for cover crop management. “We worked together across disciplines to define the research objectives for this work, and it is great to see that the resulting recommendations bring our disciplinary recommendations closer together - that we can often terminate cereal rye several weeks prior to soybean planting without compromising biomass and minimizing the green bridge for insects.”

• Bakker, M. G., Acharya, J., Moorman, T. B., Robertson, A. E., & Kaspar, T. C. (2016). "The Potential for Cereal Rye Cover Crops to Host Corn Seedling Pathogens." Phytopathology, 106(6), 591–601.

• Clark, K. M., Boardman, D. L., Staples, J. S., Easterby, S., Reinbott, T. M., Kremer, R. J., Kitchen, N. R., & Veum, K. S. (2017). "Crop Yield and Soil Organic Carbon in Conventional and No-till Organic Systems on a Claypan Soil." Agronomy Journal, 109(2), 588–599.

• Hodgskiss, C. L., Young, B. G., Armstrong, S. D., & Johnson, W. G. (2020). "Evaluating Cereal Rye and Crimson Clover for Weed Suppression within Buffer Areas in Dicamba-resistant Soybean." Weed Technology, 35(3), 404–411.

• LU, Y.-C., Watkins, K. B., Teasdale, J. R., & Abdul-Baki, A. A. (2000). "Cover Crops in Sustainable Food Production." Food Reviews International, 16(2), 121–157.

• Mirsky, S. B., Curran, W. S., Mortenseny, D. M., Ryany, M. R., & Shumway, D. L. (2011). "Timing of Cover-Crop Management Effects on Weed Suppression in No-Till Planted Soybean using a Roller-Crimper." Weed Science, 59(3), 380–389.

• Mirsky, S. B., Ryan, M. R., Teasdale, J. R., Curran, W. S., Reberg-Horton, C. S., Spargo, J. T., Wells, M. S., Keene, C. L., & Moyer, J. W. (2013). "Overcoming Weed Treatment Challenges in Cover Crop–Based Organic Rotational No-Till Soybean Production in the Eastern United States." Weed Technology, 27(1), 193–203.

• Wallace, J. M., Williams, A., Liebert, J. A., Ackroyd, V. J., Vann, R. A., Curran, W. S., Keene, C. L., VanGessel, M. J., Ryan, M. R., & Mirsky, S. B. (2017). "Cover Crop-Based, Organic Rotational No-Till Corn and Soybean Production Systems in the Mid-Atlantic United States." Agriculture, 7(4), 34.

• Wallander, S. (2021). Cover Crop Trends, Programs, and Practices in the United States.