Estimating Soybean Yields

If you read our last blog (What Makes a Bushel?), then you already know that we are concerned about bushels and ultimately yield. We spend a good amount of time looking for economical and profitable ways to drive yield higher. The fun thing about this time of year is that we begin to figure out how we performed. The yield monitor in the combine is the true measure for us, but we do spend some time trying to estimate what we should expect in the coming months.

Three Variables of Soybean Yield

Number of Pods - Soybean plants are very adaptive and fill in gaps where other plants may have failed to grow. For this reason, we are counting the total number of pods rather than the number of plants. The number of pods is set when the plant is flowering, but many potential pods will be aborted throughout the season as stresses afflict the plant.

Beans Per Pod - The number of seeds per pod is a function of hybrid, conditions at flowering, and timing of pod fill. While there may be potential for a four bean pod, some of those beans may be aborted due to insufficient moisture or nutrition while maturing beans.Typically we see three beans per pod, but two or four are not uncommon.

Seed Size - The seed size factor is rather subjective and hard to determine in soybeans. Late season rains could lead to good plant health and bigger seeds. Conversely, dry weather later in the season or an early frost would cause seeds to shrink. The cool weather and late rains we have seen in 2019 should help bean size.

Again with soybeans, we are dealing with a lot of moving targets as we try to estimate yield. Flowering is crucial as this is when the potential number pods and the beans in those pods are determined. Weather post flowering is extremely important as is will provide for the retention and filling of pods with beans of a particular size.

If you would enjoy the technical nuts and bolts of these calculations, then please continue reading. If not, then you can check out our counterpart to this blog titled Estimating Corn Yields.

Yield Check

Performing a yield check for soybeans is even more challenging than corn. For beans planted in 30" rows, we are working with 1/10000th of an acre or one row for 21". Next, we are counting the total number of pods irregardless of the number of plants. Then the average number of beans per pod is estimated and seed size is tied to a factor ranging from 15-21. These are mathematical factors found on university published charts correlating to a number of seeds per pound. More small seeds are necessary to make a pound, so the factor would be higher. Less large seeds are needed to make a pound, so the factor would be lower.

Below, you can see a couple of yield calculations. Pay close attention to the seed size factor as that is the only variable being changed. This simple example makes it quite obvious why yield estimates are far from an exact science!

EXAMPLE 1: