Estimating Crop Yields


Soil getting water

As crop start to mature, farmers are estimating crop yields. Weather conditions have been variable. Many soil are drier than normal. However, some fields have had almost perfect rains and some way too much. Expect yields to be as variable as the rainfall, even within the same field. The best way to estimate corn yield is to use the yield component method. This method was developed by the University of Illinois. The following procedure comes directly from Dr. Bob Nielson, at Purdue University.

The yield component method uses four components. These yield components include number of ears per acre, number of kernel rows per ear, number of kernels per row, and weight per kernel. The first three yield components (ear number, kernel rows, kernels/row) are easily measured in the field.

Final weight per kernel obviously cannot be measured until the grain is mature (kernel black layer) and a 15% grain moisture of 15% which is the typical moisture value used to determine a 56-lb market bushel. Consequently, an average value for kernel weight is used. Kernel numbers per 56-lb bushel are influenced by both growing conditions and hybrid genetics. Kernel weight from year to year for the same hybrid can easily vary by 20,000 kernels per bushel due to variable growing conditions during the grain filling period. Consequently, the number of

kernels per bushel can vary significantly among years or fields within years. Average kernel weight range from 67,000 to 94,000 kernels per 56-lb bushel, with an average of about 76,000 per 56-lb bushel. Crop uniformity also influences the accuracy of any yield estimation technique. The less uniform the field, the greater the number of samples that should be taken to estimate yield for the field.

Step 1: At each estimation site, measure off a length of a single row equal to 1/1000th acre. For 30-inch (2.5 feet) rows, this equals 17.4 linear feet. For other row spacings, divide 43,560 by the row spacing (in feet) and then divide that result by 1000 (e.g., [43,560 ÷ 2.5] ÷ 1000 = 17.4 ft).

Step 2: Count and record the number of ears on the plants in the 1/1000th acre of row to be harvestable. Do not count dropped ears or those on severely lodged plants unless the combine header will be able to retrieve them.

Step 3: Sample every fifth ear in the sample row, 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. Do not count nubbins or odd ears. If the row number changes, from butt to tip, estimate an average row number per ear and average kernels per row.

Step 4: Calculate the average number of kernels per ear by summing the values for all the sampled ears and dividing by the number of ears. For example, kernel counts on five ears were 490, 510, 520, 480, and 500 or 2500 kernels divided by 5 for an average of 500 kernels per ear.

Step 5: Estimate the yield for each site by multiplying the ear number (Step 2) by the average number of kernels per ear (Step 4) and then dividing that result by a kernel weight "fudge factor". Unless your seed company can provide some insight into kernel weight values for their hybrids, perform separate calculations using kernel weight "fudge factor" values equal to 65, 75, and 85. This range of values represents that most commonly experienced factors in the central Corn Belt. If grain fill was stressful, use higher kernel weight "fudge factor" values between 90 and 100. For example, if you sampled 30 total ears, the total kernels per ear averaged 500 equals 15,000 kernels. For a factor of 65, (15,000/65) that equals an estimated yield of 230 bushels. For a factor of 75, (15,000/75) 200 bushel per acre, and for a factor of 85, 176 bushel of corn per acre.

Estimating corn yields can be as much an art as a science. Due to dry conditions in the Midwest, and low water levels in the Mississippi river, barge traffic has been reduced. Locally, wheat harvest was huge and the stored wheat has been slow to be moved out. Even rail transportation had become less reliable and requires a minimum of 100 cars. Thus, the basis for grain storage is huge this year. Farmers who can estimate their yields and store it for later delivery can gain some money. Let’s have a safe harvest!