Published on Wednesday, 30 November -0001 00:00
By Dan Martens,
U of M Extension
The following information is provided by Dave Nicolai, Regional Extension Educator at Hutchinson, taken in part from the 2009 Iowa State University Corn Field Guide.
Corn growth development is now or soon to approach the "R6" stage of reproductive development. This last stage of growth occurs when a black layer forms at the kernel's attachment, blocking movement of dry matter to the kernel. At this point stress has no yield effect unless plants lodge or ears are damaged as in the case of high winds or insect feeding.
Dry down after black layer
Typical kernel moisture is about 30 percent at the R6 stage of development. Many area fields have been at this stage for the last 1 to 2 weeks or longer. After this stage drying rates are normally 0.4 to 0.8 percent moisture loss per day. Ideal harvest moisture for field corn is 15 to 20 percent, which typically occurs 2 to 4 weeks after R6. The rate of dry down when estimating time to harvest depends on the following:
¥ Cool, wet weather can lower daily drying rates to less than 0.3 percent per day.
¥ Warm, dry weather can raise daily drying rates to 1 percent per day.
¥ Late maturing hybrids dry slower than maturing hybrids.
¥ Hybrid traits associated with faster drying include thinner, fewer and loose husk leaves; ears with tips that protrude beyond the husks; early ear drop from an upright position; and thinner, more permeable seed coats.
¥ Late planted corn dries slower than early planted corn.
Estimating yield potential
Yields can be estimated in standing corn, but the accuracy will vary depending on the actual kernel weight. The use of the "kernel count" yield estimation method may overestimate in field with poor grain-fill conditions and underestimate in fields with above average grain fill conditions.
¥ Estimate the number of harvestable ears per 1/1000 acre for the length of row needed. (30 inch row spacing = 17 feet 5 inches, 20 inch row spacing = 26 feet 1 inches and 22 inch row spacing = 23 feet 10 inches).
¥ Count the number of rows of kernels per ear on every fifth ear in the measured section and calculate the average.
¥ On these ears, count the number of kernels per row and calculate the average.
¥ Estimated yield (bushels per acre) = (number of harvestable ears x number of rows per ear x number of kernels per row) divided by 90.
For more accurate estimations, repeat this process several times in a field. You can expect a fairly wide margin of error on this process, maybe plus or minus 10 percent or more.
Measuring corn field harvest losses.
Adjust harvest equipment to minimize grain loss. Two kernels per square foot left behind the combine represent one lost bushel per acre. One full ear lost per 1/1000 acre represents six to seven bushels per acre left in the field. Losses can be considerable in lodged or hail-damaged fields.
Estimating soybean yields.
a. Count plants in 1/1000 acre.
b. Count pods on 10 random plants and calculate average per plant.
c. Calculate pods per 1/1000 acre as a x b.
d. C divided by 78 = bu/a. This is based on 2.3 seeds per pod, 3,000 seeds per pound, 60 pounds per bushel. You can also calculate a seeds per pod average on sampled plants and you can calculate seed per pound for your field.
Note: Please continue to work deliberately toward a SAFE harvest season, especially with difficult field conditions.