Many farmers and agronomists noticed short soybean plants in some fields during June this year. They wonder if something can be done to spur some additional growth as flowering is fast approaching, if not already begun.
The surprise with seeing short soybean plants this year is that planting was timely. “The unfortunate situation is that after planting, we saw the onset of cool, wet, cloudy conditions,” explains Mark Licht, Iowa State University Extension agronomist. “Those weather conditions during early seedling growth resulted in shorter stem elongation between developing nodes, as well as less elongation of the petioles.”
There are concerns that short soybean plants could lead to reduced soybean yields and pods set closer to the ground. These concerns are valid if rows do not close the canopy during the last week of June or the first two weeks of July, Licht says.
“While a yield loss is not guaranteed when canopy closure does not happen, it can be expected because full interception of sunlight is not occurring as reproductive development of the soybean plants begins. A short soybean plant height does not mean a yield loss is to be expected, however. Soybean plants can easily compensate for stressful environments by adjusting pod set and seed fill with ideal conditions in August.”
Warmth best remedy
Soybean varieties grown in Iowa and the Midwest are indeterminate varieties, he notes. This means that soybean vegetative growth (new leaves and nodes) will continue after reproductive growth has begun (flowering and pod set). It is common for soybean plants to continue initiating new leaf growth past the R5 growth stage (beginning seed fill), and these new stem nodes will flower and set pods that produce seeds.
What can be done? “Nothing,” Licht says. “Some farmers and agronomists ask about the use of foliar fertilizers to spur additional growth. Foliar fertilizers will not increase the growth rate, especially if soil test levels are adequate. Additional nitrogen may make for greener soybean leaves; however, this could also increase elongation of upper nodes and increase the likelihood of late-season lodging. Warmer, sunnier weather is the best remedy to increase soybean growth rate and reach canopy closure more quickly.”
Reduce harvest losses
For fields with shorter plants that may set pods closer to the ground, you need to plan ahead to reduce losses during harvest. A Michigan State University Extension article lists several harvest considerations:
Adjust combine. On your combine, adjust the skid shoes and header angle to lower the header to pick up pods on the lower nodes. Pay particular attention to this adjustment to minimize picking up large root balls and rocks. Empty the rock trap and grease the combine more frequently to ensure proper functioning. Check guards and knife sections frequently and replace as needed.
Get “reel.” Adjust the reel speed and position to reduce gathering losses. This means lowering the reel to pull short soybean plants away from the cutter bar. Adjust the reel speed to slightly faster than the ground speed. For draper heads, the belt speed should be fast enough to pull plants away from the cutter bar.
Harvest early or late. Early morning and evening harvesting will reduce the amount of pod shattering that occurs due to damp pod occurrence.