By: Dan Davidson,
DTN Contributing Agronomist, July 9, 2015

If soybeans played politics, they would definitely fall into a red state. The plant takes a decidedly conservative stance by shedding at least 60% of its pods and flowers when it feels stressed or feels there are simply too many pods to support.

Soybean yield is based on how many seeds go in the hopper. However, what we sometimes fail to remember is that each pod contains a fairly consistent average of 2.5 seeds per pods. That means getting the plant to hang on to those pods is a critical component of cranking up yield.

Studies by University of Illinois plant physiologist Fred Below have shown that simply adding one additional 2.5-seed bean pod per plant bumps yield 2 bushels per acre. That’s a remarkable number — again… one extra pod per plant will boost yields by 2 bushels!

“Soybean plants way over do it when they produce flowers and pods and then respond to environmental factors by cutting back to what they can support,” said Below. “It’s a beautiful strategy when you think about it, and many indeterminate crops which flower over a prolonged period behave in this way.

Below and his graduate students are studying how the soybean plant produces and holds onto pods, and looking for opportunities to increase pod number. His research is being funded by the Illinois soybean checkoff.

Below has found that in Illinois, soybean plants produce about 20 nodes during the season and that yield comes primarily from the center of the main stem between nodes 6 to 15. For a 50-bushel crop, plants produced only one pod per node below node 6 and above node 15. They produce an average of 1.5 to 2.5 pods between nodes 6 and 15. For a 60-bushel crop, more of the yield comes between nodes 5 to 17 with 2.0 to 2.5 pods per nod found (see the bell curve illustration).

The University of Illinois researcher’s team found increasing the relative maturity to a fuller-season variety increased both node and pod number. However, the number of pods per node didn’t change. Adding fertilizer didn’t increase nodes, but it did increase pod number per node — primarily in the center of the plant from nodes 5 to 15.

Below believes there is a good opportunity to keep more of those potential pods in the center of the plant through better management of fertility, growth stimulants and plant health (fungicides).

“Canopy regions vary in their ability to generate yield with the middle region responsible for 50% to 60%

[of yield], compared to 10% to 20% in the bottom, top and branch regions,” Below told DTN. “We are learning that specific regions can be targeted with better agronomic management to improve yield.”

Below offers three key tips for growers wishing to produce and protect more pods:

— Plant early and use a longer maturity group to get more nodes which increases number of pods.

— Fertilize properly. Fertilization improves pod set in the middle and top regions of the plant and increases seed weight in the bottom and middle regions.

— Keep plants healthy. Foliar protection lengthens the seed filling period improving yield through increased seed weight in the top half of the plant.

Below is continuing to study pod production and dynamics in 2015 to further understand how growth stimulants can be used in conjunction with better management to improve pod number and seed weight.

“The message for growers is there is a lot of potential to add yield, and you don’t have to do that much to make a difference,” he said.

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Source – DTN – Article