It’s bound to happen sooner or later. After two years of excruciating drought, Mid-South farmers may be due a wet summer, one in which it rains at least once during the week and again on Sunday whether you need it or not.

When that happens, Trey Koger figures, planting soybeans on raised beds will result in even higher yields than he obtained in a study comparing the practice with planting them on flat ground when conditions were dry.

Planting soybeans in narrow rows (10-inch to 20-inch) or twin rows on raised beds could also significantly increase yields above planting them in wide rows (40-inch), Koger told growers attending the Rice/Soybean Production session at the Delta Ag Expo in Cleveland, Miss.

It was a swan song of sorts for Koger, who until recently had been an agronomist with the USDA-ARS Soybean Production Research Unit at Stoneville, Miss. Late last year, he moved “across the tracks” from USDA to become cotton weed scientist/agronomist with the Delta Research and Extension Center.

Koger, a native of Belzoni, Miss., reported on the soybean research projects he and other Agricultural Research Service scientists have been conducting at Stoneville and other Mid-South locations.

For openers, researchers have found that planting soybeans on raised beds increased yields by 5 to 7 bushels above soybeans planted on flat ground in flood-irrigated situations.

In small plot tests, soybeans planted on a 40-inch hipped bed produced an average of 86 bushels an acre compared to 84 bushels an acre for beans planted on 80-inch wide beds and 79 bushels for beans planted flat.

When the soybeans weren’t flooded, the 40-inch hipped bed plantings produced an average of 89 bushels per acre versus 84 bushels per acre for the 80-inch wide beds and 82 bushels for soybeans planted flat. Koger said the increases would have meant another $11 to $38 per bushel with $6 per bushel soybeans.

“The benefits of planting on raised beds in wet years should be larger than 5 to 7 bushels an acre because we saw some of those even in the presence of no imposed flood in an extremely dry year,” he said.

Koger said he and his fellow researchers have found little yield difference between narrow rows (10-inch to 20-inch spacings) and twin-rows (plantings of two 10-inch rows based on a 40-inch center) when the drainage system is equal; i.e., planted on 80-inch wide beds.

But the narrow and twin-rows do out-yield the wide rows (planted 40 inches apart on 80-inch beds by an average of 9 percent or 7 to 8 bushels per acre even when the seeding rates are roughly the same.

Earlier research involving the then-new twin-row planters indicated that it might not be necessary to increase seeding rates for those even though planter manufacturers had suggested farmers increase seeding rates by 20 percent.

“We saw very little yield difference between 120,000 plants per acre and 140,000 plants per acre in the 10-inch and 20-inch narrow row spacings and the twin-row system or in the different seeding rates for the 40-inch wide row plantings,” said Koger. “We found we could reduce seeding rates even further and not decrease yields.”

Part of the reason for the increase in the closer row spacings is that the plants produce more pods per acre. “Twin rows produced, on average, five more pods per plant,” says Koger. “That may not seem like much, but it adds up to more than a half-million more pods an acre in the twin-row system versus the number of pods in the single-row.”

He and Dan Poston, Extension soybean specialist at the Delta Research and Extension Center, believe most of the increased yield is due to light interception. “You get twice as much sunlight on the plants in a twin row or narrow row as you do with a single row,” says Koger.

The higher yields with narrow or twin rows on raised beds should offset the costs associated with putting up the beds, especially in poorly drained soils such as the heavy clays that dot the Mid-South.

The researchers have also found that farmers who are planting 90,000 to 100,000 plans in Maturity Group 4 and 5 varieties are on target for making optimum yields. If they try Maturity Group 3 soybeans, 120,000 to 140,000 plants per acre are most profitable.

“Our current recommendations have been based on the old production system,” he said. “Those are 100,000 to 130,000 plants per acre for narrow rows and 70,000 to 100,000 plants per acre for wide rows.”

Higher seed costs have led researchers to take another look at those recommendations, and they’re finding that soybean yields don’t increase much when they increase seeding rates past 90,000 to 100,000 plants per acre for Groups 4 and 5 and 130,000 to 140,000 per acre for Group 3s.

When you look at returns over seed costs, growers begin facing losses when the seeding rates goes beyond those levels for the different maturity groups. (Returns for Group 4 beans, for example, can drop nearly $40 an acre as producers keep increasing seeding rates.)

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