|Thursday, August 01, 2013 12:00 AM|
This article was written by Ed Lentz, Hancock Extension Educator.
Most of the corn plants in our area have tasseled and ear silks have emerged for pollination. Silks are female flowers that emerge from the tip of the corn ears. Tassels are the male flowers that produce pollen. Pollen shed usually begins two to three days prior to silk emergence and continues for five to eight days with peak shed on the third day.
On a typical midsummer day, peak pollen shed occurs between 9-11 a.m. (after the dew has dried off the tassels) with a second round of pollen shed late in the afternoon. Pollen shed stops when the tassel is too wet or too dry and begins again when conditions are favorable. Pollen remains viable after release for about 18-24 hours.
Each tassel contains from two-five million pollen grains, (2,000 to 5,000 pollen grains for each silk). Wind blows the pollen across the field with most of it settling within 20-50 feet of its tassel source. When a pollen grain lands on the silk, it forms a tube down the silk channel to pollinate the ovule in 12 to 28 hours. About 97 percent of the silks are pollinated by pollen from a different plant in the field.
A well-developed ear shoot should have 750-1,000 ovules, or potential kernels, each producing a silk. Under good conditions, all silks will emerge and be ready for pollination within three to five days. This usually provides adequate time for all silks to be pollinated before the end of pollen shed. Silk development begins first from the base ovules and last from the tip ovules of the ear.
By pollination, the corn plant has reached its maximum height and has produced all of its leaves. The potential number of kernels has been established and the remaining grain fill period will determine survival number and size of these kernels. Most corn hybrids regardless of maturity type will reach physiological maturity 65-70 days after pollination. Corn is “safe” from a killing frost after the black layer forms at physiological maturity. Farmers in our area desire pollination to be completed by Aug. 1 to insure maturity prior to the first killing, which is around Oct. 10 for this area. Additional information on the growth and development of corn may be found at: www.ipm.iastate.edu/ipm/files/03%20Corn%20Growth%20and%20Development.pdf
If you want to estimate your corn yield, use the following method developed by Purdue University:
• Measure off a length of corn row equal to 1/1000th acre. For 30-inch (2.5 feet) rows, this equals 17.4 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).
• Count and record the number of ears on the plants in the 1/1000th acre of row that you deem to be harvestable. Do not count dropped ears or those on severely lodged plants unless you are confident that they will be harvested.
• For every fifth ear, 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. For example, 16 rows times 30 kernels per row = 480 kernels per ear.
• Average the number of kernels per ear from several ears.
• Estimate yield by multiplying the ear number (Step 2) by the average number of kernels per ear (Step 4) and dividing by 80 for excellent to 85 for good growing conditions. The 80 to 85 values represent the range in numbers of kernels (thousands) in a 56# market bushel. Kernels are large this year due to good grain fill, cool temperatures and adequate moisture.
Example: If you counted 30 harvestable ears and sampled every fifth ear, the average kernel count was 16 row and 36 kernels per row or 576. The estimated yield for that one thousandth of an acre site would be (30 ears x 576 kernels) divided by 80, which equals 216 bushels/acre for excellent growing conditions to 203 bushels/acre for good (divide by 85) growing conditions. Some farmers are reporting 18-20 rows and 34-38 kernels per row or 700 kernels which translates to 247-262 bushels/acre corn.