Successful Farming
01-29-07
Almost a silver bullet for better bean yields
Picking the right soybean varieties can help you find the missing 20 bushels
Gene Johnston
Successful Farming magazine Managing Editor
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.
Add all this up, and Petersen says you'll find "the missing 20 bushels" from many
soybean farms:
* SCN control can add 6 bushels an acre;
* Variety selection is worth another 5;
* Earlier planting can gain 4 bushels;
* Narrower rows adds another 4; and
* Lower seed rate can gain a bushel.
* Total: 20 bushels per acre gained.
To prove his point, he pointed to tests on a farm in the well-drained soils of far
western Iowa. Those fields have low SCN pressure to start with, and by using
these best management practices, some plots produced 100-bushel soybeans in
2004 and 2005, and 98 bushels an acre last year.