Lesson 3: You Can Count On Corn

SUBJECT: Math

OBJECTIVE: Students will practice mathematical concepts using corn kernels, plants, and fields by:

• Counting the numbers of rows on an ear.
• Counting the number of kernels in a row.
• Comparing the sizes of fields by number of acres.
• Learning the dimensions of acres in feet.
• Converting miles into feet and vice versa.
• Calculating the number of square feet in an acre.
• Calculating the number of kernels in an acre.
• Learning how to count the number of ears in 1/1000 of an acre.
• Learning to use a yield-calculation formula.
• Estimating corn yields in several hypothetical fields.

EVALUATION: Students understand the mathematical concepts taught on these worksheets. Using these real-life examples make the concepts more understandable.

BACKGROUND FOR TEACHERS:

The amount of corn produced in a field is called its "yield." The number of kernels determines the yield. A high yield results from many kernels on every ear AND many ears in a field. There can be many ears, but if the weather was bad during pollination there won't be many kernels on each ear, resulting in a poor yield.

Ears can be very big, with many kernels. But if there aren't enough plants (a corn plant normally produces one ear per plant) yields will still be low. Planter problems, seed problems, insects, diseases or poor weather can all cause low yields by reducing the number of plants or ears in an acre.

If you know the number of kernels on an ear, and the number of ears, it's easy to calculate the number of kernels in an acre. If you know the number of kernels in a bushel, it's easy to calculate the number of bushels in an acre.

Corn prices are set on a per bushel basis. Therefore, the number of bushels produced affects a farmer's profitability. He or she can measure the yield during harvest by using a yield monitor connected to a GPS unit (see Unit 5), or can wait to measure it after storing the corn in a grain elevator, or after selling it.

But because the best prices are often before harvest, a farmer might want to predict or ESTIMATE how much corn is in a field before harvest begins. Then they use a yield calculation formula that calculates the number of kernels per acre, then divides by the average number of kernels in a bushel of corn (source: DeKalb Genetics Company):

1. Walk into the field a set number of paces. Establishing a predetermined pattern eliminates the natural tendency to stop where the crop appears to be better than average.
   
   
2. Measure 1/1000 acre and count the number of ears. The length of the row to measure for 1/1000 acre depends on your row spacing, as shown below. Do not count ears that have only a few scattered kernels because these won't contribute to yield.

3. Sample three ears from the measured row length. To avoid any sampling bias, take the third, sixth and tenth ears. Do not sample ears that were not included in the ear count.
   
   
4. Count the kernel rows and average number of kernels/row on each ear. Do not count tip kernels less than half size. Multiply the number of kernel rows by the kernels/row to get kernels/ear.
   
   
5. Estimate bushel per acre yield by: (number of ears x average number of kernels per ear) ,90
   
   
6. The 90 in this formula comes from the fact that a bushel of corn roughly contains about 90,000 kernels. We drop the 1,000s because we've counted the ears in 1/1,000 of an acre. If kernel size is unusually large or small, adjust the 90 to reflect this.
   
   
7. You will get a more reliable estimate of yield if you repeat steps 1 to 5 for each 10 acres in the field. You have to sample representative ears to get a reasonable estimate of yield. Selective sampling of ears or kernel sizes that vary markedly from normal will cause these yield estimates to significantly differ from actual yield.

STUDENT ACTIVITIES:

1. Ask students to read the story Claire Plays Basketball. Tell them to pay close attention to the paragraph in which Claire and her friends use tape measures to count the number of corn plants, and also the paragraph in which they learn how many rows and kernels of corn there are in an average ear.
   
   
2. Then ask students to complete Worksheet1, 2 and 3.

Last reviewed May 7, 2004