This is Dr. Nathan Mueller, your local agronomist for Nebraska Extension. Estimating soybean yields at the end of August are simply that, estimates. However, it can give us an idea of an estimated range in yields to expect to help market new crop during September prior to harvest.
Because the number of seeds per pod is a critical component, it is best to wait until soybeans reach the full seed stage called R6. The R6 growth stage is reached when seeds filled the pod cavity of a pod on one of the four uppermost nodes.
Soybean yield components are plants per acre, pods per plant, seeds per pod, and seed weight. Soybean plants have a great ability compensate when stands are thin or thick, so we don’t need to really know how many plants we have per acre, but the just the number of pods per acre and seeds per pod.
The easiest way to do this is to work with an area 1/10,000 of an acre. In 30-inch rows, cut 21 inches of row length with a small pruning shears. In 15-inch rows, cut 21 inches of row length from two rows side by side. Throw the collected plants in the bed of your pickup that count the total number of pods. Write that down. Then, select two random plants, count and write the down either 1, 2, 3 or 4 seeds that are in each pod. Add all these values together and divide by the number of pods from those two plants. The average number of seeds per pod in most years is 2.5, but I have been getting closer to 2.8 seeds per pod this year in some fields.
The biggest unknown factor is seed weight that can vary from 2,500 to 3,500 seeds per pound. Since most have had favorable conditions, I would assume at least a normal seed size of 3,000 seeds per pound or a conversion factor of 18. Finally, multiply the number of total pods by the number of seeds per pod and divide by 18 to get your estimated bushels per acre. Again, multiply the number of total pods in 1/10,000 of an acre by the number of seeds per pod and divide by 18 to get your estimated bushels per acre.
For more information on determining soybean yield and short publication on this approach, please call me at 727-2775 or visit our local website at croptechcafe.org. Know your crop, know your tech, know your bottom line. This is Dr. Nathan Mueller, your local agronomist for Nebraska Extension on KTIC radio.