Grain Crops

Home

Contacts

Reports

Dr. Chad Lee

Extension Grain Crops

859.257.3203

cdlee2@uky.edu

Dr. Jim Herbek

Extension Grain Crops 270.365.7541 ext. 205

jherbek@uky.edu

Estimating Soybean Yield

Chad Lee and Jim Herbek, Grain Crops Extension, University of Kentucky

September 8, 2005

The following are guidelines to get an estimated yield of soybean seeds while the crop is still standing in the field. Proceed with caution since variability in soybean stand, seeds per pod, and seed size can all drastically affect the final yield. These estimates become highly variable when conducted before seed fill is completed and assumptions about final pod number, seed number and seed size must be calculated.

Estimates should be made in five to ten locations across the field to get a better estimate for yield. Each of the locations selected should represent those areas of the field. Even with these attempts to get as representative a sampling as possible, there is still some variability with the yield estimates.

Estimating soybean yield is accomplished by determining the factors for the following equation:

Equation 1:

(plants per acre) x (pods per plant) x (seeds per pod) / (seeds per pound) / (pound per bushel)= (bushels per acre)

Step 1. Estimate plants per acre.  

By using the guidelines in Table 1, you can quickly convert stand counts into plants per acre. For row widths of 30, 20 and 15 inches, count the number of soybeans in 10 feet and divide that number by 10 to determine soybeans per foot. Use the number of soybeans per foot to determine soybeans per acre. For soybeans in row widths of 7.5 and 7 inches, count the number of soybeans in 40 feet of row (or 10 feet of four separate rows). Use the number of soybeans in 40 feet of row to determine the soybeans per acre.

Example: In 15-inch row soybeans, you count an average of 3.5 plants per foot of row. According to this table, 3.5 plants per foot in 15-inch rows equal 121,968 plants per acre.

If you would prefer to count soybeans in 1/1,000^th acre, then you can use Table 2 to determine the row lengths needed. When using this method, count the number of plants within 1/1,000^th acre and multiply that number by 1,000 to estimate soybeans per acre.

Step 2. Estimate pods per plant.

Pick 10 plants in a row and count the pods on each plant. Determine the average number of pods per plant.

Example: Pods per plant are counted for 10 consecutive plants. The total number of pods is divided by 10 and the average number of pods per plant is determined to be 22.

Step 3. Estimate seeds per pod.

Healthy soybean plants will average about 2.5 seeds per pod. For healthy soybeans, multiply pods per acre from Step 5 by 2.5 seeds per pod to estimate seeds per acre. For soybeans under stress, the seeds per pod could drop to 2 or 1.5 or even less under highly stressful situations. You can count the seeds per pod from the same soybean plants used in Step 2.

Example: The majority of pods lower in the canopy appear to have three seeds. The pods on the upper one-fourth of the plant have two seeds. The overall estimate of seeds per pod is 2.5

Step 5. Estimate seed weight.

In Kentucky, about 2,500 seeds per pound is an average number. Under stressful conditions, the seed size may be smaller, meaning that more seeds per pound are needed. The original seed size from the seed bag may provide the best indication of soybean seed size.

Example: The estimate used in this example is 2,500 seeds per pound.

Step 6. Estimate bushels/acre.

One bushel of soybeans typically weighs 60 pounds.

Example: Using the numbers obtained and the yield calculation, the following is determined:

(plants per acre) x (pods per plant) x (seeds per pod) / (seeds per pound) / (pound per bushel)= (bushels per acre)

121,968 x 22 x 2.5 / 2,500 / 60 = 44.72 or 48 bushels per acre

Keep the Yield Estimate in Perspective

Remember that the yield estimate is only as good as the numbers being put into the equation. Yields estimates made closer to harvest are typically more reliable than yield estimates made earlier in the growth and development of the soybean. For additional questions regarding soybean yield estimates, contact your county extension agent. 

Table 1. Estimated soybeans per acre. For 30, 20 and 15-inch rows, determine soybeans per foot of row by counting the number of soybeans within 10 feet of a row and divide the number of soybeans by 10. For 7.5 and 7.0-inch rows, determine the number of soybeans in 40 feet of row by counting soybeans in 10 feet of four separate rows.

Table 2. Row width and feet of row needed to equal 1/1000^th acre.

Back to Grain Crops Main Page | Report Archives