15-inch row soybeans

Late-planted soybeans benefit from 15-inch rows instead of 30-inch rows. The 15-inch rows allow soybeans to capture light, which boosts yield. 

COLUMBIA, Mo. — Several management practices may add a little extra yield to late-planted soybean, says University of Missouri Extension soybean specialist Bill Wiebold.

Record-breaking wet weather set back soybean planting greatly in May. Wiebold’s research shows average yield for soybean planted in the third week of June drops by 25% compared to soybean planted in early May.

Yield depends on captured sunlight. Late-planted soybeans face a disadvantage because daylight periods shorten during seed filling. Managing soybean to increase light capture may improve yield potential, Wiebold says in an Extension news release.

He suggests these key management options:

  • Plant in narrow rows.
  • Increase seeding rate at least 30,000 seeds/acre.
  • Limit soil compaction as much as possible.
  • Treat seeds with a fungicide.
  • Keep “normal,” adapted maturity group.

Plant in narrow rows to let plants capture available sunlight sooner in a shortened growing season.

Wiebold tested row width and planting date in a two-year experiment in central Missouri. In his research, yields improved in 15-inch rows rather than 30-inch rows later in the season. Yields improved 8% in soybeans planted in mid-May. Yields improved by 14% when planted in 15-inch rows in the third week of June.

Wiebold found no yield difference between 15-inch row spacing and drilled soybean in 7.5-inch rows in full-season soybean.

“However, as planting date gets pushed later into June, one might consider using a drill,” he says.

He also offers a word of advice on using grain drills: “Remember, drills are challenged to control seed depth and soil closure. You may want to increase seeding rate if using a drill for planting.”

Late-planted soybean plants produce fewer main stem nodes and smaller or fewer branches. Pods form at nodes, and yield corresponds to the number of nodes. Growers need to increase the number of plants when plants produce fewer nodes.

Farmers will want to increase seeding rates in later-planted soybeans, Wiebold says. He found almost no yield increase in fields planted in early May with more than 120,000 plants per acre. However, he recommends a stand density of at least 150,000 plants per acre in late-planted soybeans.

Soil conditions this year are likely to be less than optimal for planter operation, he says. Carefully monitor soil conditions. Try to balance possible yield loss from additional planting delay with potential yield effects from soil compaction.

“Carefully adjust the planter to reduce compaction near the seed and provide the best possible environment for early root growth,” Wiebold says. “Seed treatments, especially fungicides that protect against Pythium and other fungi, will also aid stand establishment and early vigor. Because of a shortened season, rapid root growth and leaf production will help improve yield potential.”

Wiebold discourages changing maturity group unless planting is delayed into July.

“Late-planted soybean plants may be smaller, and that reduces sunlight capture,” he says. “Early-maturing varieties that are not adapted to your location are less likely to produce the number of nodes and leaf area to maximize yield potential than adapted varieties.”