UNIT
1: 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):
- 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.
- 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.
- 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.
- 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.
- Estimate bushel
per acre yield by: (number of ears x average number of kernels per
ear) ,90
- 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.
- 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:
- 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.
- Then ask students
to complete Worksheet1, 2 and 3.
