Estimating Corn & Soybean Yields

October 2, 2015

Estimating Corn & Soybean Yields

Each year about this time I get calls from farmers wanting to estimate their yields and each year I look it up, print off a sheet or two, put it in the mail or try to explain it to someone over the phone. I struggled with math in school when it was on a paper in front of me so trying to explain it over the phone is really stretching my comfort zone... and the person on the other end of the line’s ability to comprehend what I’m trying to explain.

Anyway, if you google it, there are dozens of websites that detail various methods on how to do this. I’m going to try to summarize a couple of those that I thought were easier to follow here. I must give credit to my colleagues at Purdue for this information.

Estimating Corn Yields

1.               Calculate the row length in 1/1,000th of an acre. Divide 43.56 by the row spacing (in feet) to get the feet of row in 1/1,000th of an acre. For 30" row spacing (2.5'), that’s 17' 5" of row. (43.56/2.5 = 17.4' or 17' 5")

2.               Count and record the number of ears on the plants in the 1/1000th acre of row that you deem to be harvestable. Don’t count nubbins, dropped ears, or severely lodged plants the combine won’t get.

3.               For every fifth ear in the 1/1,000th of an acre, record the number of complete kernel rows per ear and average number of kernels per row. Then multiply each ear's row number by its number of kernels per row to calculate the total number of kernels for each ear.

4.               Calculate the average number of kernels per ear by adding the number of kernels for all the sampled ears and dividing this total by the number of ears.

5.               Estimate the yield for each site by multiplying the number of ears (#2) by the average number of kernels per ear (#4). Here comes the tricky part! Divide this total by an estimate of the number of kernels per bushel.

6.               On average, a bushel of corn with a test weight of 56 pounds and 15.5% moisture would have about 85,000 kernels per bushel. Since our calculation is for 1/1000th of an acre, divide by 85. This number can vary greatly depending on the growing conditions and hybrid genetics. It might be as low as 65,000 or as high as 100,000 kernels per bushel (divide final figure by 65 to 100).

7.               For example, assume you had 30 harvestable ears in 1/1,000th of an acre; had an average of 510 kernels/ear on the ears your counted; and you assumed the kernel size was average. Your estimated yield would be 180 bu/A (30 ears x 510 kernels/ear = 15,300 / 85 factor = 150 bu/A)

8.               Repeat this process at several representative spots in the field to get a better estimate for the yield in that field.

Estimating Soybean Yields

1.               Count the number of pods in 1/10,000th of acre. If in 30" rows, count the pods on plants in 21 inches of one row, for 15" row spacing count the pods on plants in 21" of two rows; for 10" row spacing count the pods on plants in 21" of three rows; and for 7.5" row spacing count the pods on plants in 21" of four rows.

2.               Estimate an average number of seeds/pod. A good starting point is to estimate 2.5 seeds per pod, then increase or decrease that average by your observations in the field.

3.               Calculate the number of seeds in 1/10,000th of an acre by multiplying the number of pods (#1) by the average number of seeds per pod (#2).

4.               Estimate your yield by dividing the number of seeds in 1/10,000th of an acre by a seed size factor. For average size soybean seeds (3,000 seeds/pound), divide by a factor of 18; for large soybean seeds (2,500 seeds/pound), divide by a factor of 15; for small soybean seeds (3,500 seeds/pound), divide by a factor of 21.

For example, if we estimated 360 pods in 1/10,000th of an acre and an average of 3 seeds per pod and we estimated the seed size to be average: 400 x 3 = 1,080 / 18 = 60 bushels/acre yield

Repeat this process at several representative spots in the field to get a better estimate for the yield in that field.