Is it better to harvest corn early and save more of the corn or leave it in the field longer to dry and save on fuel for artificial drying?
That's the question many Minnesota corn producers are considering, says Lyon County educator Bob Byrnes of the University of Minnesota Extension Service.
Byrnes recommends making a careful estimate of potential harvest losses as a first step in answering the question. "Check non-Bt corn for ear droppage potential and all fields for stalk rot," he says. "For ear droppage potential, pick four representative locations in each field. Then examine and test 25 consecutive plants at each location. Examine ear shanks for corn borer tunnels or frass (debris from tunnels). Tug each ear downward. Tunneled ear shanks will usually snap off or bend when the ear is tugged.
"Count the number of tunneled ear shanks, and add the number from the four counts. The total is the estimate of the percentage of potential harvest loss. Multiply this percentage by the expected yield to determine the possible harvest loss in bushels per acre."
As ear shanks dry they become more brittle and susceptible to droppage, especially when hit by strong winds, notes Byrnes.
He suggests checking stalk lodging potential by pushing each plant several nodes above the ear. Push plants at least a foot from vertical, and count plants that break off or bend (lodge) below the ear.
"The only practical way to estimate harvest loss from lodged, goosenecked and downed plants is with the combine," says Byrnes. "Run the combine in both directions at a couple of locations at least 300’ from the field border, and measure ear loss."
To do this, says Byrnes, mark off 1/100th of an acre in a width equal to the width of the combine and centered over a harvested combine pass. Calculate the length of this area by dividing the number 435.6 by the combine harvesting width in feet. For example, with a combine having a six-row head (30" rows) and a harvesting width of 15’, the length for 1/100th of an acre is 29’ (436.5 sq. ft. divided by 15 ft. = 29 ft.).
Each 0.75-lb ear on the ground in the marked off area represents a bushel-per-acre loss, says Byrnes. Smaller ears on the ground can be measured in terms of how many 0.75-lb ears they would make.
"In good conditions with a properly adjusted combine, the ear loss should be less than 1 bu/acre," says Byrnes. "Reducing ear loss may require harvesting at slower speeds or in only one direction. This would mean slower harvest and starting harvest early."
Harvesting earlier, when corn moisture levels are higher, increases drying cost. Factors affecting drying cost include yield, LP gas price and corn price. Byrnes cites the example of a 100 bu/acre corn yield, a corn price of $1.75/bu, and an LP gas price of 69¢/gallon. In this example it costs $7.35 to remove an extra five percentage points of moisture. This would equal the value of 4.2 bu of corn per acre.
Corn price, gas price, yield and moisture percentage points to remove vary among individual corn growers, notes Byrnes. He suggests the following formulas to calculate exact bushels per acre necessary to pay drying cost:
Drying cost (cents/pt/bu) = [LP gas price ($/gallon) x 0.02] + [electricity price ($/KWH) x 0.01]
Bushels/acre to pay drying cost = [Drying cost (cents/pt) x number of pt of moisture to dry x yield (bu/acre)]/corn price ($/bu).
Source: Bob Byrnes, 507-537-6702