Estimating Soybean YieldsSeptember 3, 2013 | Category: Agronomy |
It is very hard to estimate soybean yield accurately in a field. Soybeans have a great ability to compensate for various growing conditions. Pod number, seeds per pod and seed size all play a role in calculating soybean yield.
Pod number: early to midseason stresses can limit how many pods are retained.
Seeds per pod: determined by the growing conditions shortly after flowering. It is possible for late season stress to reduce this number, but late season rains cannot add more beans per pod.
Seed Size: late season rains can increase yield by extending the seed fill period and creating a larger sized soybean. 3000 seeds/pound would be considered normal. 2500 would be large, while 3500 would be small. It’s this factor that I believe causes the largest spot for error when we are out in the fields today. My example below demonstrates this point.
Formula (I have attached an example in bold)
1) Calculate your field population for where you are standing. Laura Johnston has a great article to help you with that here. (160000)
2) Select 10 random plants in each sample area and count the number of pods. Calculate the average number of pods (25)
3) Calculate the number of pods per acre [plant population x average number of pods]
(4 000 000)
4) Calculate seeds per acre [pods per acre x estimate of seeds per pods], likely close to 2.5 seeds per pod (10 000 000)
5) Calculate pounds per acre [seeds per acre ÷ an estimate of seeds per pound] for the example, I used 3000 (3 333)
6) Estimate yield [pounds per acre ÷ 60 pounds per bushel] (55.6 bu/ac)
Seed size is a huge factor in determining soybean yield. If I use the same example above but change to a large seed (like what was harvested last year – 2500 seeds per pound), yield goes from 55.6 to 66.7 bu/ac.
The key to creating accuracy is by sampling more areas in a field and becoming better at determining the number of seeds per pound.
Kirk Van Will, CCA-ON, Maizex Seeds Yield Specialist, West Middlesex & Lambton Counties