Narrow row soybeans don't need higher plant population
Heather Thorstensen
Date Modified: 12/01/2009 11:35 AM
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Agri News staff writer
WORTHINGTON, Minn. -- Some Minnesota soybean producers tried narrow row planting, got white mold and switched back to wider rows.
But narrow rows, which are 22 inches apart or less, may not have been the reason white mold developed, according to Lizabeth Stahl, University of Minnesota Extension educator in crops.
"It's not necessarily the row spacing," she said. "...It seems to be more of a function of the (plant) population."
In the past, growers would increase plant population when switching from 30-inch rows to narrow rows, but research has found it does not need to change.
Seth Naeve, Extension soybean agronomist, recommended these soybean seeding rates in a April 23, 2008, edition of "Minnesota Crop News":
In excellent to ideal planting conditions, growers using maturity Group II soybeans should plant 140,000 live seeds per acre; maturity Group I should be planted at 150,000 seeds per acre and maturity Group 0 should be planted at 160,000 seeds per acre.
These rates will help growers reach U of M-recommended harvest populations. Southern growers should shoot for approximately 100,000 plants per acre. The number increases for growers farther north.
Trials conducted throughout the state have shown a yield advantage for soybeans grown in narrow rows.
One U of M study at Lamberton from 2000 to 2005 found on average a 7.6 percent yield increase in 10-inch rows compared to 30-inch rows.
According to Naeve in the crop newsletter: "We have seen a five bushel per acre increase when moving from 30-inch to 10-inch rows. About half of this was noted between 30-inch and 20-inch rows, and half was seen between 20-inch and 10-inch rows. Therefore, 22-inch rows should provide about a two bushel advantage over 30-inch rows, but are probably at a two bushel disadvantage when compared with 15-inch rows."
A National Agricultural Statistics Service survey in 2008 found the average soybean row width in Minnesota was 23 inches. Most of the farms in the survey, about 49 percent of 128, had row widths between 28.6 inches to 34.5 inches.
About 23 percent of farmers planted in rows that were 10.1 to 18.5 inches apart.
"There's still people planting soybeans in narrow rows," said Stahl.
White mold remains an issue in some areas. Although plant population may be more of a culprit in these instances than row spacing, one management recommendation could be to return to wider rows to increase air movement to make the environment less inviting for mold.