Shake the Disease? Plant Reduced Soybean Pops
In Bob Lindeman’s soybean rows, planting populations are on a general decline, and the reduction is not about saving dollars up front, but on combating mold and rot.
“In my area, I see everything from 150,000 even down to 90,000, but this is not about savings on seed,” Lindeman says. “The biggest driver is disease control to let air flow inside the canopy, while at the same time, maintaining or gaining yield.”
“Farmers have to find the right planting population balance on their own ground and not drop too much,” he adds. “Major reductions in population look attractive at the outset, and guys sometimes hit good yields, but if you lower your seed rate too much, the weather will slam you around the corner.”
Get Low?
Roughly 60 miles southwest of Minneapolis, Lindeman grows 1,200 acres of corn and soybeans, and helms Lindeman Seeds in southcentral Minnesota. On relatively flat ground in McLeod County, he works 1,200 dryland acres of heavy, dark soils—ripped with reside left on top.
Every year, after corn, Lindeman seeds soybeans. “We’ve been pushing beans a little earlier. Some guys in my area plant beans before corn, but not me. My beans, if conditions are right, go in the last of April. In the past, it was May 8-10 before we started planting beans.”
At a depth of 1.5”, Lindeman plants soybeans from a 1 to 2.2 maturity group, on 22” single rows. “There are guys around on solid 7-10”, and some on 15”, 22”, and 30”—it varies according to farm.”
Lindeman’s soybean planting population ranges from 130,000-140,000 seeds per acre (spa). A decade back, he planted at 150,000-155,000 spa, and stretching backward to his first crop in 1981, he planted at 160,000 spa. “If I’m planting what I consider to be a large structure soybean plant, I’ll cut back to 130,000. If I’ve got a smaller structure plant, I’ll keep it at 140,000.”
“In my geography, 150,000 used to be average, but more guys today are at 130,000-135,000. I even know a guy who recently went in at 90,000-95,000.”
“I’ve seen trial data around here showing great yields at 110,000-120,000, but the problem is you don’t know when bad weather is coming. If that weather arrives and you’ve got low populations, you run the risk of serious yield loss. Start out too low and then lose some stand—you can get hurt bad.”
Beware the Blitz
Disease elimination is the driver factor when reducing soybean planting rates for many Upper Midwest growers, according to Seth Naeve, University of Minnesota soybean agronomist.
Naeve cites highly visual white mold as culprit No. 1. “Farmers easily see white mold and they also see the yield monitor drop. White mold is tangible and manageable. However, when you can see something, sometimes you overcompensate, as opposed to soybean cyst nematode that growers can’t track and often blindly manage without any genuine knowledge of the yield impact. White mold is different and growers work hard against it.”
During many crop years, hot August temperatures burn off white mold and reduce disease pressure, but when in summers with cooler and wetter conditions after canopy closure, white mold can blitz a field.
“What happens is we can go several years with no white mold and growers get lulled into false sense of safety,” Naeve describes. “Then along comes a bad weather year and they get nailed and frustrated. White mold can certainly take away 20 bushels, so it must be managed up front because present fungicide control is not great. And the best defense is managing population in spring.”
However, finding an ideal seed rate is a tall task, evidenced by the variation Naeve sees—from 120,000 spa on many farms to 200,000 spa on operations in Minnesota’s extreme north. “Farmers ultimately have to plant what they’re comfortable with, and there probably isn’t a right answer to population. If they’re too conservative on seeding, there is downside risk that they’ll give up a couple bushels, and if they put more money in seed, they can make sure they have enough seed on every acre to maximize yield and make the money back. But I don’t believe it’s a hell of a lot of difference either way.”
Even variable rate seeding is not an exact population answer, Naeve contends. “The current state of art in soybean tech is for farmers to look at historical yield maps and take the lowest yielding areas and boost the seed rate accordingly, and sometimes take the highest yielding areas and decrease the seeding rate. This is primarily for saving seed costs, and they probably doing a good job.”
However, Naeve questions the prescriptions. “It’s tough to predict what a given area will do the next year. I certainly think opportunity is there to variable rate, but right now, I think farmers are going after variable rate a little blindly, and probably not using the best prescriptions. I’m not saying they’re hurting themselves by doing it, but I am saying they may not be helping a ton. An area of future research for us is the variable rate seeding question—for sure.
Tender Loving Care
Lindeman delivers a final point of emphasis: compensate for lower populations. “If you cut population, you better put on really good seed treatment and really good root promoter, and good inoculant. You’re not doing it to cut costs. Sure, you take some away from the price of the soybean up front, but I do believe you must treat the seed in the right way.”
“The new genetics allow us to use lower populations, but we’re all dealing with more prevalent disease,” Lindeman adds. “Therefore, treat your seeds with TLC to get the best outcome.”
For more from Chris Bennett (cbennett@farmjournal.com 662-592-1106) see:
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