As he looks across his fields spanning the flat terrain of northern Iowa, Mike Riggert isn't just seeing rows of soybeans. He's thinking about ways to adjust his seeding rates.
"For years, we planted a flat rate of 150,000 seeds per acre, but we've definitely cut back on seeding rates in the last two or three years," says Riggert, who farms with his brother, Brian, near Whittemore.
It's a targeted process for Riggert, who plants soybeans in 30-inch rows and has been experimenting with variable-rate seeding. In some cases, he has dropped rates as low as 80,000 or 90,000 seeds per acre. In other places, like high-pH areas that tend to stunt the plants, Riggert has planted 175,000 seeds per acre. In fields with neutral soil pH and adequate fertility, he typically plants 120,000 seeds per acre.
"You can get good yields with lower planting populations if you pay attention to detail," says Dan Bjorklund, seed team leader for MaxYield Cooperative, which serves the Riggert farm. "Mike planted slow enough to singulate, and he's counting 80 to 100 pods per plant where the seeding rate is 120,000."
Riggert saw no yield loss with his lower planting rates in 2018. "Those areas didn't yield more than expected, but they yielded the same as when we used higher seeding rates in years past. We came out ahead, because we didn't plant more seeds than necessary."
Deciding the right seeding rate is one of the most influential factors for increasing soybean profitability since seed cost is one of the most expensive inputs.
"I've been in this business 20 years, and farmers have talked about soybean seeding rates every year," states Seth Naeve, a University of Minnesota Extension soybean agronomist. "The thing to remember is that different fields respond differently to various planting populations."
Soil type, soil fertility and weather conditions affect final stand establishment. "We don't look at variable-rate seeding as a way to get more soybean bushels," Naeve adds. "It's really a way to save on seed costs."
Ignacio Ciampitti, an associate professor of crop production and cropping systems at Kansas State University, teamed up with Corteva Agriscience to study optimal plant density by yield environment.
Researchers created a soybean database of seeding rates ranging from 69,000 to 271,000 seeds per acre, including final number of plants and seed yield. The results were classified by low-yield environments (less than 59.6 bushels per acre [bpa]), medium-yield environments (59.6 to 64.1 bpa) and high-yield environments (more than 64.1 bpa). They found that:
> Optimal plant density decreased by 24% from low (127,000 plants per acre) to high (97,000 plants per acre) yield environments.
> The optimal density ranged between 109,000 to 144,000 plants per acre for the low-yield environments; from 77,000 to 114,000 plants per acre for the medium-yield environments; and 76,000 to 117,000 plants per acre for the high-yield environments.
"It's a myth that one of the best ways to increase soybean yield is just to plant more seeds," Ciampitti says. "It depends. In a high-yield environment, you might be planting too high of a seeding rate. In a low-yielding environment, you might need to increase your soybean seeding rate."
NO YIELD DRAG
Joe and Suzanne Shirbroun have found this to be true on their northeast Iowa farm. They began experimenting with various soybean seeding rates in 2015 through the Iowa Soybean Association's On-Farm Network, which offers research opportunities focused on agronomics, cropping systems and more.
"Standability issues pushed us," says Joe Shirbroun, whose fields near Farmersburg are defined by rolling hills. "We were growing high-yield beans, but they were falling down."
The Shirbrouns, who plant in 15-inch rows, had been seeding a flat rate across all their soybean acres to get about 150,000 plants per acre. "We didn't realize that having planting prescriptions would pay for soybeans like they do for corn," says Amos Troester, the Shirbrouns' Pioneer seed associate.
The Shirbrouns began experimenting with lower plant populations in higher-yielding environments. "We can get down to 90,000 plants per acre in the low-lying areas, while our highest seeding rate is about 160,000 in other areas," Suzanne Shirbroun says. "We didn't see any yield drag with the lower seeding rates. Our yields were maintained, or they went up."
KEEP IT SIMPLE
How does geography impact soybean seeding rates? A series of studies financed by the United Soybean Board was conducted in 2012 and 2013 across the Midwest and Mid-South to examine high-input soybean production practices. Results showed that maximum yields were obtained between 100,000 and 165,000 seeds per acre across all nine states.
In the southern states (Arkansas, Kansas and Kentucky), seeding rates between 130,000 to 170,000 seeds per acre were needed to obtain maximum yields. This response was consistent across production systems, regardless of whether they included a large number of yield-enhancing treatments like seed treatments, fungicides, growth promoters, etc.
"You might assume you'd need much lower seeding rates in the South and higher seeding rates in the North, but that wasn't always true," Naeve says.
Don't get too concerned about specific prescriptions, however, he adds. Keep things simple, agrees Shawn Conley, a soybean and small grains specialist at the University of Wisconsin. "It's not worth your time and money to hire someone to write a planting prescription. Buy a bag of seed per acre. Each bag contains about 140,000 seeds. Plant 120,000 seeds in higher-producing areas and 150,000 seeds in lower-producing areas."
Also, stay focused on Agronomy 101 basics. "Soybeans require management, just like corn," Bjorklund says.
Maintain a good soil-fertility program focused on potassium -- a vital nutrient for soybeans, Conley says. Plant seeds 1 to 1.25 inches deep, ensuring good seed-to-soil contact. Also, plant as early as possible, as long as soil conditions are fit. "You get one chance to do it right," says Bjorklund, who notes that mudding in beans can cause compaction, which can hinder seedlings from emerging evenly.
Riggert began planting his 2019 beans on April 25. "This was much earlier than ever before," he adds. "The earlier-planted beans at lower populations have been superior, though, when you start counting nodes and pods."
Seed treatment is another key to success, especially with early-planted soybeans, Riggert says. It helps protect seedlings from diseases lurking in cold, wet soil, including sudden death syndrome. "When you start dropping your seeding rate, you need a strong seed treatment program," Bjorklund says.
Control weeds by using preemerge programs, multiple modes of action and a residual program to manage yield robbers such as waterhemp, Conley says. "While farmers get bored with the basics and want to talk about applying nitrogen or using molasses to boost soybean yields, the basics still matter the most," Conley notes.
As for seeding rates, start small if you want to try cutting back. "Take baby steps," Joe Shirbroun advises. "Take 20 acres of your farm, and learn from that."
Copyright 2019 DTN/The Progressive Farmer. All rights reserved.