Short Soybeans

By Mark Licht

Many farmers and agronomists are noticing short soybean this spring. Some are pondering if there is something that can be done to spur some additional growth as flowering is fast approaching, if not already begun. The surprise with short soybean is that planting was timely. The unfortunate situation after planting was the onset of cool, wet, cloudy conditions. These weather conditions during early seedling growth have resulted in shorter stem elongation between developing nodes as well as less elongation of the petioles.

There are a couple concerns that short soybean could lead to reduced soybean yields and pod set closer to the ground. These concerns are valid if rows do not close canopy within the next two to three weeks. While a yield loss is not guaranteed when canopy closure does not happen, it can be expected because full radiation interception is not occurring as reproductive development commences. Soybean height does not mean a yield loss is to be expected. Soybean can easily compensate for stressful environments by adjusting pod set and seed fill with ideal conditions in August.

Side Note: soybean grown in Iowa, and the Midwest, are indeterminate varieties. This means that soybean vegetative growth (aka new leaves and nodes) will continue after reproductive growth has begun (aka flowering and pod set). It is common for soybean to continue leaf initiation 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. Some farmers and agronomists are wondering about the use of foliar fertilizers 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.

Plan ahead with these harvest considerations for shorter soybean that may set pods closer to the ground (Staton, 2019).

• Adjust the skid shoes and header angle to lower the header to pick up pods on the lower nodes. Pay particular attention 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.
• Adjust the reel speed and position to reduce gathering losses. This means lowering the reel to pull short soybean 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.
• Early morning and evening harvesting will reduce the amount of pod shattering that occurs due to ‘damp’ pod occurrence.