Corn harvest  has begun and every field will be different this fall. Some fields will be highly productive, and others will barely pay the harvesting costs. Some fields will have good stalk strength and other fields have already gone down, with heavy lodging from wind, fragile stalks, rootworm or some other reason.
If you are fighting an uncooperative cornfield, there are some good tips that can make life easier and your efforts more profitable.
Harvest losses can be one of several types, say University of Tennessee researchers, “The following four losses with a combine are:
- Preharvest losses are parts of the crop that are detached from stalks or pods and lying on the ground prior to harvest. These losses should not be charged to the machine.
- Gathering unit losses are losses caused by the header or picker unit of the combine. These losses are usually 90% of the total harvest loss.
- Cylinder losses include unthreshed seeds or kernels that are passed out the rear of the combine. These losses are only about 5% of the total losses from modern combines.
- Separation losses are threshed seeds or kernels that are carried out the rear of the combine with the crop residue. These losses are about 5% of the total harvest loss with modern combines.”
The Tennessee researchers also want you to know that you are not going to get every kernel, so don’t worry about some grain loss, “Ideal combine efficiency is 97% for most harvested crops. This figure means that acceptable losses are 3% of the crop. No machine is capable of harvesting 100% of the crop. Average harvesting losses are closer to 10% in most crops. This indicates that a producer can increase crop harvest and reduce losses by improving combine operation skills and efficiency.”
At Ohio State University, researchers say most of the loss occurs because the grain never gets into the combine, particularly in a droughty year, “Growers need to consider the impact of premature plant death on corn maturation. Within fields, significant variation in grain moisture may exist among plants that died prematurely and those that matured more normally. In such fields, growers should be prepared for stalk lodging problems (associated with drought stress) that may slow harvest and contribute to yield losses. The loss of one “normal” sized ear per 100 feet of row translates into a loss of more than 1 bu./acre. In fact, an average harvest loss of 2 kernels/square foot is about 1 bu./acre. Keep in mind that most harvest losses occur at the gathering unit. Average gathering unit losses accounted for about a 1.2 bu./acre loss out of the total 1.5-bu./acre machine loss. The results indicate that approximately 80% of the total machine loss is caused by corn never getting into the combine.”
Wet or moldy grain
Your corn may still be wet, but stalk strength is poor, and more goes down every day with a slight breeze. How do you decide whether to sacrifice the lost bushels or pay for drying wet grain? Ohio State offers a formula to decide: bu./acre sacrificed to pay for drier grain = drying costs (cents/% moisture) x difference in grain moisture % (harvest now vs. waiting) x yield (bu./acre) divided by corn price ($/bu.).
At Purdue, researcher Bob Nielsen says if you are waiting for the black layer to appear in corn, it will always appear whether the corn is mature or prematurely dies. And he adds, “Premature kernel black layer development is usually accompanied by smaller than desired kernels and resulting ‘rubbery’ ears that can be difficult to shell without re-adjusting combine settings.”
Nielsen also says that severely lodged corn will be more likely to have molds or kernel sprouting if ears were in contact with the ground, “The prolonged contact or near contact with the moisture and higher humidity of the soil surface will delay grain drying and increase the risks of the development of fungal ear molds and premature kernel sprouting prior to harvest. Growers will be challenged to find the best compromise in grain moisture between the standing and lodged plants. The combination of variable grain moisture, possible kernel molds and premature kernel sprouting all increase the challenges of successfully storing the grain in good condition.”
The issue becomes, how should the combine be operated, to gather the most ears into the feeder house. University of Missouri researchers suggests these points:
- Run the combine engine at its rated engine speed.
- Use a ground speed of 2.8-3.0 mph. (Do not regulate ground speed by reducing engine speed.) To determine ground speed, count how many 3-ft. steps you can take in 20 seconds while walking beside the machine. Divide this number by 10 to get the ground speed in miles per hour.
- Close the stripper plates or snapping bars only enough to prevent ears from passing through.
- The chain flights over the stripper plates should extend beyond the edge of the plates about 1/4 in.
- Ears should be snapped near the upper third of the snapping roll.
- Drive accurately on matched rows, spaced according to your harvesting machine.
- Gathering snouts should float on the ground, and gathering chains should be just above the ground.
- Measure losses and make corrective machine adjustments whenever crop conditions change.
At Iowa State University, ag engineer Mark Hanna says determine where the problem areas are and harvest those first, and he says weak stalks would take precedence over corn that is already near the ground. He suggests measuring your initial losses, so you have a baseline from which to make further combine adjustments. Each ear per 436 square feet equals a loss of 1 bu./acre.
Hanna’s recommendations for combine operation to reduce losses include:
- Set gathering chains for more aggressive operation with points opposite each other and relatively closer together. Adjust deck plates over snapping rolls only slightly wider than cornstalks so that they hold stalks but not so narrow that stalks wedge between the plates.
- Operate the head as low as practical without picking up rocks or significant amounts of soil.
- Single-direction harvesting against the grain of leaning stalks may help. Evaluate losses though before spending large amounts of time dead-heading through the field.
- Limited field measurements suggest a corn reel may or may not help limit machine losses; however, a reel likely allows greater travel speed and improves productivity. Losses may be similar comparing harvest at 1 mph without a reel and 3 mph with a reel, but harvest goes much faster. Spiral cones mounted atop row dividers or the addition of higher dividers on each end of the cornhead are other potential after-market harvest aids.
- If harvest speeds are significantly reduced, the amount of material going through the combine is reduced. Fan speed may need to be reduced to avoid blowing kernels out of the combine. Rotor speed may need to be reduced to maintain grain quality. Check kernel losses behind the combine and grain quality to fine tune cleaning and threshing adjustments.
- Grain platforms have been used to harvest corn in relatively severe cases. More cornstalks and material other than grain enters the combine. Expect capacity to be reduced somewhat. Concave clearance may need to be increased for increased throughput and fan speed may need to be increased to aid separation in the cleaning shoe.
The 2011 harvest season may be as difficult as the planting and growing season. Many farmers will face fields with heavily lodged corn, others with stalks that will disintegrate as they hit the gathering chains. It is important to proceed slowly, making adjustments as the crop changes and realizing that some grain will be left on the ground. It will take a strong will to get through a challenging harvest, and everyone from the combine operator to the truck driver will have to have the right mental attitude.