Almost a silver bullet for better bean yields
There is no silver bullet to better soybean yields, but one practice comes close: Spend more time picking the soybean varieties you plant, with special attention on seed that is resistant to soybean cyst nematode (SCN).
Iowa State University soybean expert Palle Pedersen made that point at an Iowa State Crop Advantage meeting for farmers last week in northern Iowa. After three years of experimental work on high soybean yields at three locations across Iowa, he's confident about the "no magic bullet" statement. But, "The SCN varieties we have today are really good. There's no yield drag now, and that's very different compared to what you may have tried in the 1990s," he told growers.
They should be checking fields for the presence of SCN, especially if they are in the heavy, poorly drained soils of central and northern Iowa, where SCN proliferates. Start by taking multiple soil samples, mixing them, and having them tested at a lab.
In experiments near Boone, Iowa, Petersen says that he has seen yield differences as high as 24 bushels per acre between SCN-resistant seed and non-resistant seed planted the same day. Your seed dealer should be able to help you find varieties that are suited to your level of SCN intensity. "The extra minutes you spend in soybean variety selection can give you some of your greatest returns," Petersen said.
He emphasized other factors that have the potential to bump up soybean yields, including:
- Planting date
May 15-20 used to be considered ideal planting date for soybeans in Iowa. Petersen now thinks ideal in southern Iowa is about April 25, and in northern Iowa it is May 1. "Our work says that if you plant by those earlier dates, there's a 79% probability of greater yields than if you plant on May 15 or later," he said. Earlier planting leads to earlier canopy, and brings the plants' flowering stage earlier into the growing season.
"Soybean yield is actually made in mid-July, when the seeds are set based on flowering," Petersen said. "People think that soybean yields are made in August, but in August, you are only saving the yield that was made in July."
- Row spacing
Petersen said there's a four- to five-bushel-per-acre advantage to 15-inch rows compared to 30. It's all about earlier canopy, maximum light interception and plant density.
- Seeding rate
"All you need is 100,000 plants per acre at harvest to achieve maximum yields," he said. "In fact, more plants than that may actually be detrimental to yields, because if you crowd the plants you create more potential for foliar diseases." He recommends you plant 120,00 to 140,000 seeds per acre in order to achieve 100,000 plants at harvest.
If you use a drill to seed beans, you may bump up the planting rate a little. "Farmers tend to drive too fast with drills, and they bounce around and some of the seeds don't get good soil contact. It's OK to use a drill, just slow down," Petersen cautioned.