Terminating Cereal Rye After Seeding Soybeans (Or Not!)
This research was funded by the Walton Family Foundation.
In a Nutshell:
- Jon Bakehouse and Sam Bennett are interested in maximizing the benefits of cover crops to their soil, livestock, weed management and bottom lines. The objective of this research was to determine how long growth of a cereal rye cover crop in soybeans can be prolonged without sacrificing yield and profitability
- The cooperators hypothesized soybean yields would be statistically similar among the treatments and weed control would be best the longer they delayed cover crop termination.
- For Bennett, while the gains in rye biomass that occurred with each successively later termination date did result in less weed pressure, those same gains also translated to lower soybean yields as well as losses in profitability of more than $60/ac.
- At Bakehouse’s, all four treatments required rescue herbicide applications for weed control, although fewer strips of the treatments that delayed termination until the soybean’s first trifoliate required this. The treatment in which Bakehouse allowed the cereal rye to grow with the soybeans the entire year saved him nearly $16/ac compared to when he terminated the rye after soybeans emerged. However, terminating at the same time as planting soybeans saved him $46/ac compared to delaying until soybean emergence and $62/ac compared to allowing the rye to grow through the year.
- Two years of this on-farm research have shown that it is possible to delay rye termination up to 27 days after planting without sacrificing soybean yield but that careful management under drought conditions is critical in order to avoid soybean yield loss.
Sam Bennett and Jon Bakehouse conducted on-farm research in 2019 to determine how long they could extend the growth of a cereal rye cover crop after planting soybeans before it would interfere with the soybean crop. They compared two termination dates in relation to planting soybeans – near-plant termination and delayed termination. That year Bennett was able to generate more rye biomass by delaying termination until 27 days after planting soybean, and he did so without sacrificing soybean yield. Wet weather prevented Bakehouse from terminating rye until much later than intended (24 and 52 days after planting), but he made an important observation: in the strips where he was forced to delay termination until 52 days after planting soybean, a green cereal rye cover crop emerged the subsequent spring. The cereal rye had set and dropped seed prior to being terminated in 2019 then emerged as a “self-seeded” (and free!) cover crop in 2020.
Eager to push the envelope and determine precisely how long they could prolong the growth of a cereal rye cover crop in their soybeans without sacrificing yield and profitability, as well as intrigued by the possibility of simply not terminating the cover crop, Bennett and Bakehouse made some modifications and conducted the research a second year. In 2020 they compared differences in cover crop biomass, weed pressure, soybean stand count, soybean yield and profitability of four termination treatments:
- At-plant – Cereal rye terminated at time of soybean planting
- Emerged – Cereal rye terminated just after soybean emergence (VE)
- Trifoliate – Cereal rye terminated after first soybean trifoliate leaf unrolls (V1)
- Self-seed – Cereal rye is not terminated. It is allowed to grow with soybeans, mature and drop seed.
Ultimately, both Bakehouse and Bennett are interested in maximizing the benefits of cover crops to their soil, livestock, weed management and bottom lines. Bennett remarked, “I hope to use this data to maximize the benefits we can capture by using a cereal rye cover crop. I’d like to contribute to data that could change the way RMA [USDA Risk Management Agency] regulates cover crop termination guidelines.” Bennett was referring to RMA guidelines that restrict cover crop termination dates in western Iowa to on or before the date of planting soybeans in order to qualify for crop insurance.
Following corn harvest in fall 2019, Jon Bakehouse and Sam Bennett planted cereal rye (var. Elbon) at a rate of 55 lb/ac. Bennett seeded rye aerially on Sept. 14, and Bakehouse drilled rye in 8-in. rows on Oct. 24. The subsequent spring, they planted soybeans in 15-in. rows. Bennett planted soybeans on April 27, 2020, at a population of 139,000 seeds/ac, and Bakehouse planted soybeans on May 12 at a population of 130,000 seeds/ac.
Bakehouse established treatment strips by chemically terminating rye in his at-plant treatment strips on the same date of planting soybeans (Table 1). Bennett was prevented from terminating rye in his at-plant treatment due to wet weather. Subsequent termination dates and products used in each treatment are detailed in Table 1. Cooperators arranged treatments randomly in neighboring strips and replicated treatments 4 times for a total of 16 strips at each farm (Figure A1). This arrangement allowed us to conduct statistical analyses to assess the effects of termination date on cover crop biomass, weed pressure, soybean stand count and soybean yield. Treatment strips measured 60 ft by 1,140 ft at Bennett’s and 30 ft by 590 ft at Bakehouse’s.
Weed control at Bennett’s consisted of a tank-mix of Prowl 3.3 EC (3 pt/ac) and Salvo (12 oz/ac) applied to all strips on April 12 (15 days before planting soybeans). Three days after planting soybeans, Bennett applied Authority MTZ at a rate of 10 oz/ac.
Bakehouse observed “lots of little pigweed” in the at-plant strips by June 12 and applied a tank mix of Liberty (28 oz/ac), Anthem Maxx (3.5 oz/ac), AMS (3 lb/ac) and adjuvant the same day only to the at-plant strips. On July 25, heavy weed pressure in the other treatments necessitated a rescue application of Liberty (28 oz/ac), Anthem Maxx (3.5 oz/ac), Zaar (1 pt/ac) and AMS (3 lb/ac) to one strip of the trifoliate treatment, three strips of the self-seed treatment and all four strips of the emerged treatment. Bakehouse commented, “I do not think the rescue spray in the self-seed treatment affected the rye in those strips. It didn’t kill the weeds that were very large at that point, and I don’t think it was able to reach weeds below the canopy.”
Bakehouse and Bennett sampled cereal rye biomass on the same date the rye was terminated in all but Bakehouse’s self-seed treatment strips and Bennett’s at-plant treatment strips (Table 2). They sampled biomass by cutting aboveground rye biomass from within quadrats of a specified area and collecting it into paper bags. After allowing the biomass to dry, the cooperators weighed each of the samples and determined the amount of rye biomass (lb/ac) in each treatment at the time of termination.
Soybean stand counts were carried out at Bakehouse’s on Sept. 2 and at Bennett’s on Sept. 24 (Table 2).
Both cooperators sampled weed pressure in each strip by counting the number of weeds inside a quadrat of a fixed area. Each cooperator conducted seven counts in each strip. Bakehouse sampled weed pressure between the dates of Sept. 2 and Sept. 9. Bennett sampled weed pressure on Sept. 24 (Table 2).
Bakehouse and Bennett, respectively, harvested soybeans on Oct. 5 and Sept. 24 (Table 2). Yields and percent moisture were recorded for each strip, and yields were adjusted to standard moisture (13%).
Following soybean harvest in fall 2020, each cooperator additionally measured the percentage of groundcover generated from seed that dropped earlier in the season from the unterminated cereal rye in the self-seed treatment strips. To measure percent groundcover, Bakehouse and Bennett counted the number of green cereal rye plants at 32 fixed points along a 16-ft distance in each self-seed strip. Bakehouse and Bennett measured groundcover on Oct. 16 and Nov. 3, respectively.
To evaluate effects of delayed termination on cover crop biomass, weed pressure, soybean stand count and yield, we calculated treatment averages for each measurement then used Tukey’s tests to compute least significant differences (LSDs) at the 95% confidence level. The difference between each treatment’s average of a given measurement is compared with the LSD. Differences greater than or equal to the LSD indicate the presence of a statistically significant treatment effect, meaning one treatment outperformed the other and the cooperators can expect the same results to occur 95 out of 100 times under the same conditions. A difference that is less than the LSD indicates the difference is not statistically significant and the treatment had no effect.
Results and Discussion
Cover crop biomass at termination
At Bakehouse’s, the emerged and trifoliate treatments generated more rye biomass than the at-plant treatment (Table 3). Bakehouse did not measure biomass in the self-seeded treatment. Biomass in the emerged and trifoliate treatments was statistically similar despite approximately the same period of time passing between sampling biomass in the at-plant and emerged treatments as passed between sampling the emerged and trifoliate treatments (Table 2). Low rainfall during the month when biomass was sampled in the emerged and trifoliate treatments may be responsible for the minimal rye biomass gains in Bakehouse’s trifoliate treatment strips relative to the gains that occurred between his emerged and at-plant treatments (Figure A2).
Heavy rainfall at the time of planting soybeans prevented Bennett from sampling and terminating rye biomass in his at-plant treatment strips, but he did sample biomass of the self-seeded rye (Figure A2). The self-seeded rye generated more biomass (sampled Aug. 15, 2020), than either the trifoliate (June 1) or emerged (May 15) treatments had at the time of their termination (Table 3). Additionally, the trifoliate treatment generated more biomass than the emerged treatment.
Soybean stand count
Delaying rye termination as well as not terminating rye (self-seed) did not reduce soybean stand counts at either cooperator’s farm (Table 4).
Bakehouse experienced no difference in weed pressure among his treatments (Table 5); however, because his weed assessments were conducted after rescue applications of herbicides, these data are less reliable. On June 1, the same date of terminating rye in the emerged treatment strips, Bakehouse observed many small weeds in the emerged treatment but only a small amount of larger weeds in the trifoliate and self-seed treatments. By June 12, the date of terminating rye in the trifoliate treatment strips, Bakehouse observed that weed pressure in the trifoliate and self-seed treatments continued to remain low while the at-plant treatment contained lots of small pigweed and required a rescue herbicide. By July 25, all four strips of the emerged treatment required a rescue herbicide as well as one strip of the trifoliate treatment and three strips of the self-seed treatment.
For Bennett, weed pressure was lowest in the trifoliate and self-seed treatment strips compared to the emerged treatment strips (Table 5).
Fall 2020 groundcover
Bakehouse and Bennett measured 31% and 76% groundcover, respectively, in their self-seed treatments.
Yield in Bakehouse’s at-plant treatment was greater than yield in all three other treatments (Figure 1). With respect to cover crop termination date, the earliest termination (at-plant) produced the greatest yield and the later treatments (emerged, trifoliate) produced lesser yields (Table 3).
At Bennett’s, yield in the emerged treatment was greater than yield in the trifoliate and self-seed treatments, and yield in the trifoliate treatment was greater than in the self-seed treatment (Figure 1). Just as with Bakehouse’s results, Bennett’s yield data showed that as rye termination date is delayed, soybean yields decrease (Table 3). Bennett’s yield data are additionally made more interesting by the fact that weed pressure was greater in the treatment where soybean yield was greatest (emerged) while lower weed pressure in the trifoliate and self-seed treatments corresponded with lower yields (Table 5). For Bennett, while the increasing gains in rye biomass that occur with each successive termination date reduce weed pressure, more rye biomass (resulting from delaying termination) also has the effect of reducing soybean yield, likely due to competition from the rye.
At Bakehouse’s, the ROI (return on investments) in his at-plant treatment ($389.97) was greatest – $62.94/ac greater than in emerged, $62.58/ac greater than in trifoliate, and $46.68/ac greater than in self-seed (Table 6). Greater soybean yield contributed to the greater ROI in the at-plant treatment. Although the costs of rye termination and rescue herbicide applications were variable among the at-plant, emerged and trifoliate treatments at Bakehouse’s, the total costs of each treatment were similar. Thus, the greater yields in the at-plant treatment resulted in greater revenue and a greater ROI compared to the emerged and trifoliate treatments. The difference in ROI between the self-seed and at-plant treatment was not quite as large as the differences in ROI between the at-plant treatment and the other treatments. This is because the total costs of the self-seed treatment were nearly half the total costs of the other treatments. However, the lower costs were not enough to counteract the lower revenue generated from reduced yields in that treatment.
At Bennett’s (Table 7), the ROI for emerged was $60/ac greater than the ROI for trifoliate and $117.80/ac greater than the ROI for self-seed. The greater yield and revenue coupled with the same total costs as the trifoliate treatment are what allowed the emerged treatment to generate a greater ROI. Although the self-seed treatment required zero dollars of additional cost per acre compared to the emerged and trifoliate treatments, its significantly lower yield reduced the ROI.
Conclusions and Next Steps
For Bennett, while the gains in rye biomass that occurred with each successively later termination date did result in less weed pressure, those same gains also translated to lower soybean yields as well as losses in profitability of more than $60/ac. At Bakehouse’s, all four treatments required rescue herbicide applications for weed control, although fewer strips of the trifoliate and self-seed treatments required this than the at-plant and emerged treatments. While Bakehouse’s self-seed treatment saved him nearly $16/ac compared to the emerged and trifoliate treatments, his at-plant treatment saved him $46/ac compared to the same treatments and $62/ac compared to the self-seed treatment.
Two years of this on-farm research have shown that it is possible to delay rye termination up to 27 DAP without sacrificing soybean yield but that careful management under drought conditions is critical in order to avoid soybean yield loss. At the conclusion of this trial Bennett commented, “It was hard to predict that drought would affect the results by as much as they did. I can’t help but wonder how the soybean yields would have been affected if we harvested the rye over top of the beans, or if the rye would have laid down flatter if we had more rain to help break it down through the season” (Figure A2).
In the end, both Bakehouse and Bennett were happy to have conducted the trial. “Any trial that helps me to get the most benefit out of my cover crops is worthwhile. While the yields and results weren’t what we were hoping for, we learned a lot about the boundaries of managing the cover for a specific purpose,” Bennett remarked. Bakehouse added, “The second year of this trial really started to hone in on specific questions that can’t necessarily be answered in one year, especially when compared with data from years prior.”
Appendix – Trial Design and Weather Conditions
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- Gailans, S., J. Boyer and T. Sieren. 2018. Terminating Cereal Rye Cover Crops After Planting Soybeans. Practical Farmers of Iowa Cooperators’ Program. https://practicalfarmers.org/research/terminating-cereal-rye-cover-crops-after-planting-soybeans/ (accessed March 2021).
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