Uniform emergence of corn stands can greatly impact potential yield. Studies we’ve conducted here have shown corn emerged beyond 48 hours, while still contributing to yield, do not result in as much yield per plant as the first emergers. We wanted to know if this was true for soybeans. How much impact does uniform emergence have on yield potential? What kind of timeframe are we looking at to consider “uniform” emergence? And what can we do to improve emergence?
A little background….
There is significantly less published literature about uniform emergence in soybeans than there is for corn. We did manage to find a few studies that covered this topic. Literature from Michigan State University Extension states that soybeans emerged around a six day timeframe would be considered sufficiently uniform. Emergence can extend to 15 -20 days in challenging environmental conditions. Emergence this late is not ideal as it can lead to reduction in yields. Similar publications from Pioneer posits that while uniform stands are important, soybeans respond much better to uneven emergence and stands than many other crops. A study from Purdue University shows that if soybeans emerge when the rest of the stand is already at VC, they will only contribute about 20% to yield. If soybeans emerge when the rest of the stand is at V2, they likely will not contribute to yield at all. Time from VC to V2 is around 10 days. Finally, a study out of North Carolina is most similar to what we were trying to discover. They found that there was a slight increase in yield between days three and four, however as time from planting increased, there was a decrease in yield. Overall, between plants emerged on day one verses day four, there was an average of 13 bushels per acre increase.
Our Study…
We wanted to test this ourselves. We had four different locations in Brown and Richardson Counties. At each of these sites, we flagged soybeans as they emerged in 12 hour intervals. Each 12 hour group was marked with a different color flag to differentiate among the groups. This was done until all plants in 1/1000th of an acre were flagged. We monitored these plants through the growing season and up to harvest. At harvest, each plant was pulled, number of pods per plant counted and grouped by emergence date. In three of the studies, four to six plants were selected, and number of seeds per pod was calculated to use as an average for calculating yield. In the fourth study, number of seeds per pod was counted for every plant by every emergence date and used for yield calculations. We will be discussing these sites, OP1, OP2, OR1, and SH1. Two of the sites, OP1 and OP2 were both considered “early planting” with OP1 planted on April 12th, and OP2 planted on March 22nd. OR1 and SH1 were both in what we would consider a more normal planting timeframe, May 13th and May 17th respectively. Populations ranged from 104,000 to 124,000 plants per acre. Average pods per plant ranged from 33 to 41 pods per plant.
Results…
Figure 1 shows the percent of total yield by emergence timeframe for all four sites. The two “normal” planting date sites, OR1 and SH1, shown in shades of red, both emerged in a shorter timeframe than the early planted sites, OP1 and OP2, shown in shades of blue. These sites took 60-252 more hours to emerge than OR1 and 84-276 more hours to emerge than SH1. This can likely be attributed to soil temperatures at time of planting. Cooler and wetter soil conditions will slow emergence, particularly in the March 22nd planted field. Those planted in May likely had a much more consistently warm soil bed to aid in fast and even germination. Looking specifically at the two normal planting date fields, we see that not only was emergence completed by 84 and 108 hours, but also over 70% of yield was emerged in the first 24 hours. This is mainly due to the sheer number of plants emerged in that timeframe. 61% of the total stand had emerged in the first 12 hours in field SH1, and 34% of plants had emerged in that same timeframe for OR1. Bushels per plant was very uniform across all emergence dates, suggesting that yield potential is not reduced beyond 24 hours and that plants emerging after that point were still setting similar size and number of pods as the very first emerged. Figure 2 shows the bushels per plant for each emergence date on SH1. Yield per plant ranged from 0.43-0.66 bushels per plant but did not appear to be correlated with time from emergence.
While bushels per plant was also similar for OR1, the initial emergence dates did appear to have higher yields than the later emerged plants. However, the range still was fairly small at 0.5-0.8 bushels per plant. This is seen in Figure 3.
Switching to the early planted studies, OP1 and OP2, we see much more variation in overall time of emergence, bushels per plant, and number of plants emerged per day. Plant emergence was much more drawn out with only 10% and 17% plants emerged in the first 12 hours for OP1 and OP2 respectively. This resulted in only 12% and 21% of yield for that same timeframe. This low emergence amount was not hugely impactful on total yield for OP1 (figure 4), as the majority of average bushels per plant, both in and out of the first 12 hours, were around 0.65. The last two emergence dates were outliers to this with average yield per plant at 0.39 and 0.32 bushels per plant. Here we are beginning to see some impact for late emerging plants. In this case, these plant emerged after 96 hours and 168 hours. OP2 (figure 5) shows a more drastic representation of this pattern with the average yield 0.73 bushels per plant in the first 48 hours, then dropping to 0.53 bushels per plant between 72 and 144 hours, and finally trailing to 0.14 bushels per plant beyond 264 hours. This field site shows a clear disadvantage for plants emerging later.
For the early planting dates, the most impact seems to be beyond 96 hours. Prior to that point, the results were fairly similar to the normal planting dates. Additionally, the impact overall appears to be fairly negligible compared to the more drastic results we see with the corn studies.
Impact of shortened emergence
We wanted to know, how much would yields improve if we could shortened emergence below 96 hours? How much of a yield benefit would this bring? What about a more drastic scenario where emergence all occurred within 48 hours?
In the case of OP1, whose actual emergence extended to 168 hours, shortening this window down to 96 hours would gain an additional 0.5 bushels per acre. If we shortened this window to 48 hours, we would gain an additional 1.4 bushels per acre. Why was this not more dramatic? When you look at the average bushels per plant per day we see that up until the last two emergence dates, the weight was fairly uniform. 8000 plants emerged after that date, and assuming the yield was the same as those emerged at 96 hours, there was only a 0.07 bushel difference per plant from that point on resulting in a very small yield increase.
OP2’s actual emergence was the longest of all the studies and lasted 360 hours. If we shortened the emergence window on this field to 96 hours (a reduction of 264 hours, or 11 days) the yield gain would be 1.76 bushels per acre. This increase is not larger due to the fact only 25% of plants emerged beyond 96 hours, and of those plants, over half had bushel per plant weights that were similar to those emerging from 48-96 hours. However, if we look at shortening the time frame to 48 hours, this is where we begin to see a drastic improvement. An additional 15 bushels could be gained by shortening the emergence below 48 hours. Prior to 48 hours, only 45% of yield had been set. In those initial 48 hours, the average yield per plant was 0.73 bushels per plant. The average yield after that point was 0.4 bushels per plant. By shortening before 48 hours, an additional 0.3 bushels per plant was possible. Figure 7 displays this drastic difference in yield potential for OP2.
Scenario analysis for the fields planted at a “normal” planting date show much less response for shortening the emergence window. In fact, in field OR1, shortening the planting window to 96 hours resulted in a reduction in yield by 0.9 bushels per acre. In this case, the final plants emerging between 96 and 108 hours had more bushels per plant than those emerging at 84 and 60 hours, and only about .15 bushel per plant less than those at 24 hours. There would be a marginal increase of 1.6 bushels per acre for all plants emerging prior to 48 hours. The faster emergence resulted in a much more uniform result for bushels per plant. Figure 8 shows the yield potential for OR1 scenario analysis.
Even less yield could be gained for field SH1 by shortening emergence. Since all plants were emerged prior to 96 hours, no scenario analysis could be conducted for the 96 hour scenario. When looking at the 48 hour scenario, a yield advantage of 0.17 bushels per acre was calculated. The average bushels per plant was so similar across all emergence dates, no date posed a significant disadvantage for emergence. This field site seems to indicate that emergence below 96 hours will result in fairly uniform yield potential by plant. Figure 9 shows the similarity between actual yield, 96 hour scenario, and 48 hour scenario.
It is extremely important to note on all of these sites that more data and replications are needed to actually determine the validity of these timeframes. We can use this data to make some conjectures about optimum timeframe for emergence. Based on our anecdotal evidence, we can make a few conjectures:
• The fields planted later had shortened emergence, likely due to warmer soil conditions that are favorable for emergence.
• Shortening emergence below 96 hours appears to result in more uniform bushels per plant, particularly in locations where over 70% of plants had emerged in the first 24 hours. These sites also showed around 70% of yield emerged in the first 24 hours, mostly due to volume of plants emerging.
• Earlier planted fields resulted in prolonged emergence and less bushels per plant for later emerged plants
• These reduced yields resulted in an increase in yield for both the 96 and 48 hour scenarios between 0.5-15 bushels per acre in the early planted fields
• Overall, while yields were still 60-72 bushels per acre in the early planted fields, there was still room for improvement at these locations.
• Less improvement was possible for the later planted fields.
• Early planted soybeans may be of benefit if plants can emerge in a timely manner—prolonged emergence is of detriment to yield
What can we do to improve emergence?
There are a limited number of things that can be done to improve emergence. There are a host of factors that we can not control such as rainfall amounts, soil temperature and texture, crusting, issues with residue, cold water imbibition, among many others. Some of the factors we can control include planting factors such as planting depth, downforce, and closing wheels. Optimum depth is around 2 inches. Deeper will not have as uniform emergence and may struggle more with crusting. Shallower may run out of moisture prematurely and not finish emergence. Too much downforce may cause sidewall compaction and seed trench compaction. Closing wheels not getting good closure of the seed trench will allow seeds to dry out without good seed to soil contact.
Issues with disease and insects also can impact emergence. As tempting as it is to cut back on seed treatments at planting to save money, this can drastically reduce the stand we get, which affects total yield. But it also affects the timeliness of emergence, which we see can also affect yield. Make sure to spend the extra money on a good lineup of seed treatments for early season diseases and to protect against insect pressures on seeds and seedlings. The most important factor is to get seeds germinated and out of the ground. Skipping a product that is proven to help protect emergence is not likely a good way to save money.
Soybean Emergence Studies
Interested in contributing to these studies in the future? Let a team member know and we can get an emergence study set up on your farm. Its relatively little time and effort for you—so let us know if we can include a study on your farm!
Resources
https://www.pioneer.com/home/site/us/agronomy/soy-stand-seedrate-no/
http://www.canr.msu.edu/news/assessing_soybean_emergence
https://www.canr.msu.edu/news/identifying_and_responding_to_soybean_emergence_problems
https://www.channel.com/agronomics/Documents/AgronomicContentPDF/SoybeanEmergenceandEarlyGrowth.pdf
http://ncsoy.org/article/uniform-emergence-important-soybeans/
https://www.indianaprairiefarmer.com/print/14499
https://www.wallacesfarmer.com/print/43060
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