Growers want tall soybeans that canopy over the row and have lots of nodes and a few lower branches to produce a lot of pods. Plant these same varieties in Illinois prairie soils and they grow 5 feet tall and begin to lodge with some corresponding yield loss. And the varieties we grow today were largely developed and tested under 30-inch row spacing and still perform best in that 20- to 30-inch spacing.
Dr. Richard Cooper, retired soybean breeder who worked both at the University of Illinois and then at The Ohio State University, has long advocated growing dwarf soybeans in solid seeded systems (drilled in 7.5-inch rows). His breeding and agronomy work in the 1970s and 1980s repeatedly showed that dwarf soybeans seeded in ultra-narrow rows out-yielded more conventional soybean varieties both in wider (5.7 bu/A) and narrow rows (21.5 bu/A).
What is a solid-seeded semidwarf system? Semidwarf variety is not just a shorter plant. To create a semidwarf, Cooper crossed a northern indeterminate type with a southern determinate type, added in an early flowering trait, selected lines that were about a foot shorter and then advanced the best to commercial releases. He discovered that these lines excelled when planted before May 15 and solid-seeded in 7-inch rows at 250,000 to 300,000 seeds per acre. While breeding and testing Cooper discovered that semidwarf varieties not only overcame lodging, but when planted in 7-inch rows at a high population, soybeans yielded in the 80- to 100-bushel rang. This was back in the 1980s when yields were only in the 40s and 50s.
Cooper explained in an interview back in 2013 that the semidwarf yield excelled when solid-seeded, but not when planted in 30-inch rows. “I realized that the reason we probably don’t see a consistent yield advantage in narrow row soybeans with traditional indeterminate bushier varieties is because most of these varieties were bred to maximize yields in 30-inch rows. Those bushier varieties produce too much vegetation for 7-inch rows, creating lodging and disease problems. To maximize yields in 7-inch rows, breeders need to breed varieties that maximize yields in 7-inch row spacing. This is where the semidwarf varieties excel, resulting in record yields.”
To Cooper’s continued dismay, seed companies never picked up on the potential yield increases that could be achieved with semidwarf varieties and solid seeding. Recently, he posted an op-ed in CSA News titled “Semidwarf Soybeans Show Potential for Major Yield Breakthrough in the Midwest.” He continues to advocate for the semidwarf solid seeded system and recommends that commercial seed companies begin breeding appropriate varieties.
Commercial seed companies today still develop varieties with more conventional heights and focus on yield and defensive traits. In addition, soybean seed costs have skyrocketed the past two decades with all the traits and yield potential, so growers are dropping seed rates from 180,000 to 150,000, and now down to 130,000, and maintaining yield while saving money. In addition, we know that drills or air-seeders capable of solid seeding aren’t accurate enough for placing soybean seed at 150,000 or 200,000 seeds per acre when they were designed to pour out 1 to 1.3 million seeds per acre. While the semidwarf system seems intriguing, there are other logistical aspects that are discouraging.
Research coming out of Dr. Fred Below’s Six Secrets is beginning to show that varieties don’t respond equally to high levels of management. With the potential increase in yield that may accompany adopting the semidwarf system, how much greater may that yield bump be with high management? One can only dream of the possibilities.
Agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at firstname.lastname@example.org