A variety of factors go into estimating the yield potential of a soybean field. Soybean yield potential is built on the genetics selected, management decisions during the season and the weather. Yield components of soybeans are pods, seed size and number of seeds per pod.
"Individual plant production varies, and every field will vary based on pests, soils, fertility and other factors," says Shaun Casteel, a soybean specialst at Purdue. "But I've simplified the process of estimating soybean yields so that producers can scout multiple areas quickly while maintaining representative estimates."
Casteel's has devised a system based on estimated yield in one ten-thousandth of an acre. The basic formula involves multiplying the number of pods by the number of seeds per pod, then dividing that result by the seed size factor. That calculation will show the estimated bushels per acre.
To calculate, producers first need to count the number of pods in one ten-thousandth of an acre, an area determined by a 21-inch length of a row of plants and how far apart the rows were planted.
"Nearly 90% of our… soybean acres are planted in 30-, 15- or 7.5-inch rows, so just remember that each count needs to be 21 inches long," Casteel says. "You will count the number of pods in one row for 30-inch width, two rows for 15-inch and four rows for 7.5-inch."
Producers should count the number of pods that are at stage R5 or higher - when they can see seeds.
Next, they must determine the number of seeds per pod. Casteel said using the average of 2.5 seeds per pod is best because there can be a range of 1-4 seeds per pod.
"This value is conservative since we don't know exactly how the rest of the season will finish," Casteel says.
Changing this one value can increase or decrease yield estimates.