It has been a pretty good year for corn and soybeans across the Corn Belt and many of you may be wondering about your potential crop yields. For corn, the yield component method is a pretty good indicator of yield and if you do enough subsamples in a field you will get a pretty good idea.
However, soybean yield is notoriously difficult to predict even though the math seems fairly simple: plants per acre x pods per plant x seeds per pod x weight per seed and then convert that value to bushels. If it works for corn it would seem it would work for soybeans. However, the numbers of each component are so highly variable that yield calculations are unreliable.
Laura Lindsey, soybean extension specialist at The Ohio State University, stated in her recent extension article on estimating soybean yield
, “Proceed with caution when estimating soybean yield. It is difficult to accurately predict soybean yield because of plant-to-plant variability, and fall weather conditions can influence seed size. Estimates are more accurate later in the growing season and on uniform stands.”
Lance Tarochione, DEKALB®
agronomist and former CCA Soy Envoy, wrote on the folly of estimating soybean yield
, “(Estimating) soybean yield is as simple as seeds per acre divided by seeds per pound divided by 60 lbs. per bushel. The tricky part is getting a count of seeds per plant that represents the “average” plant in the field, then getting an accurate estimate of how many of those “average” plants there are, and then estimating what the “average” seed size will be. Each one of these steps is a likely source of significant error.”
These errors compound themselves, creating an unreliable yield estimate.
The best time to begin to estimate yield is at R6. Flowering has stopped, final pod set is almost complete, and seeds are filling. However, yield estimates can still be variable because final pod retention determination, seeds per pod determination and seed size can be affected by environmental stress during the next 4 to 6 weeks. If you really want to estimate soybean yield, follow these steps:
- Count the number of plants in 1/1000th of an acre (30” rows that are 17’ 5” length).
- Count the number of pods (containing one or more seeds) from 10 plants selected at random within that row and divide by 10 to calculate the average.
- Count the number of seeds from 10 pods selected at random across the row or use 2.5 seeds per pod as a constant.
- Estimate seed weight: Average year 3,000 seeds/lb., stressful year 3,500 seeds/lb. with small seeds, in a bumper year with late season rains and longer filling season, reduce to 2,700 to 2,800 seeds per lb.
- To calculate yield in bushels per acre: [(plants/1,000th acre) x (pods/plant) x (seeds/pod)] ÷ [(seeds/pound) x 0.06]
Soybean agronomist Daniel Davidson, Ph.D., posts blogs on agronomy-related topics. Feel free to contact him at firstname.lastname@example.org or ring him at 402-649-5919.