At a Glance
- Best decision may be doing nothing.
The soybean is a very forgiving plant with the ability to recover from stresses thrown at it during the growing season.
Farmers should keep this in mind when they are thinking about replanting or repairing a soybean stand damaged from frost, floods or pests, such as deer, insects or disease. “A lot of times the best decision may be doing nothing,” says Manni Singh, Michigan State University Extension soybean specialist.
Singh joined other Extension soybean specialists from across the country in a March 24 Science for Success webinar where specialists offered guidelines to farmers concerned about poor or damaged stands. Singh acknowledged that it is human nature to want to do something when a soybean stand looks shabby after taking a hit from rough weather or pests, but he encourages farmers to think it through before replanting.
In short, Singh says it is critical to know your plant population thresholds. If you are below threshold, the best option may be to repair plant rather than replant. It’s important to remember that soybean plants have a remarkable ability to compensate for open space by developing axillary branches that set additional pods.
A fact sheet produced by the Science for Success team points out that the minimum stand required to produce 95% of a full yield has been found in research to be as low as 50,000 plants per acre.
The specialists note that this differs across regions, but in most situations, it likely takes 70,000 to 75,000 healthy and uniformly distributed plants to reach 95% of your yield potential. In warmer regions and with later-maturing varieties that develop more vegetative growth, this threshold can be lowered by 10,000 to 15,000 plants.
Don't destroy existing plants
Singh and the other specialists emphasized that destroying existing plants and starting over is not the way to go when a soybean stand is damaged. The best approach, if the stand is below threshold, is to plant additional seed into existing stands. However, even then, farmers need to determine if it is economically viable and practical to plant more seed.
University of Wisconsin Extension Soybean Specialist Shawn Conley notes that soybean plants have a significant amount of phenotypic plasticity, with a great ability to regrow and fill in gaps. This means soybeans can recover from frost injury, wildlife injury, or insect damage.
“If we break the stem above the cotyledons in these early vegetative growth stages, there’s generally no yield loss associated with damage at that point. For the most part, we generally see very little damage of yield loss in the vegetative growth stages, be it frost, insect damage, or chemical drift, as long as the axillary meristems at the cotyledons or above remain intact,” Conley emphasized.
Certainly, one big factor when considering replanting is the availability of seed. University of Arkansas Extension Soybean Specialist Jeremy Ross says farmers need to know how long it will be before seed can make it to the farm and loaded into the planter to repair a damaged stand.
“The longer it’s delayed, as we delay planting, our maximum yield is reduced. If it’s going to take us two to three weeks to get this seed in, we are losing maximum yield. The question is, especially on some of our more popular varieties, can we even get the seed that we planted? Many times, especially on some of these more popular varieties, some of the new varieties, they may be spoken for, and we are not able to get the exact variety that we planted originally then come back in with a replant, so we really need to look at other varieties and try to find the best options we have available,” Ross says.
Right seeding rate
The specialists also highlighted the importance of seeding rates in maximizing yields and profitability. Singh noted that 100,000 plants per acre used to be the go-to number, but he believes that number has changed, and farmers can often get by with less plants per acre and still make their desired yield. He said seeding rate trials at Michigan State show that a stand of 75,000 to 80,000 plants per acre, uniformly distributed, will still allow you to maximize yield and profit.
Laura Lindsey, Extension soybean specialist at Ohio State University, said you want at least 100,000 plants per acre, but if you drop down to 80,000 plants per acre, it should not be an issue when it comes to yield and profit.
“But I don’t recommend people plant 100,000 because if you plant 100,000, you’re probably not going to get 100,000. I usually recommend farmers in general plant 140,000 seeds per acre. There could be some variability because you want to get to that 100,000 stand. In soil that may have higher disease pressure or soil crusting, you may need to go a little bit higher. If you have a field with better emergence and conditions, you could go lower,” Lindsey said.
In Arkansas, Ross says a uniform plant population of 75,000 plants per acre is needed to maximize yield. He said farmers will see a reduction in yield when the number drops below 75,000 plants per acre. The key is uniformity across the stand.
“If you start to get pickup truck size areas where there’s no plants, or if you get three, four, five-foot skips within a row, that’s really where we start to see an impact in our yield. As long as its uniform, I feel confident that 75,000 plants per acre will maximize yield,” Ross said.
“But I can’t tell you what the seeding rate is you need to plant to get that exactly 75,000 because in each lot of seed, the germ is a little bit different, the vigor is a little bit different, the planting conditions are a little bit different.”
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