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  • Writer's pictureRachel

Combine Adjustments: Setting You Up for Success

Taking a little bit of time to make the appropriate combine adjustments for grain retention can go a long way towards increasing harvest efficiency. We talked last week briefly about specific combine settings we may need to make to compensate for a drought stressed crop. This week we will cover combine settings more in depth, as well as harvest logistics for a more time efficient harvest.

We will cover combine settings by the three main operations the combine completes: picking, threshing, and cleaning.


The first step in the harvest process is picking. The adjustments we make to the corn and soybean heads have a large impact on harvest efficiency. 60% of corn harvest losses and up to 90% of soybean harvest losses occur at the header. So what can we do to reduce this loss at the head? First, set the gap between the deck or stripping plates. In normal years, this should be around 1.25 inches. In a year with smaller ear sizes, reduce this distance to 1 inch or below. Try this initial setting and adjust narrower if there is a lot of butt shelling occurring, and wider if stalks are becoming wedged between the plates. Additionally, the plates should be about an eighth of an inch closer together at the front than the back of the plates. The gathering chains should extend about a quarter inch beyond the snapping plates to appropriately feed the crop in. Our goal in this stage is to get the maximum amount of ears in with the minimum amount of forage material fed through the system. By reducing the amount of trash fed into the system, the threshing and cleaning processes are made much easier.


The adjustments made to the cylinder or the rotor have large effect on overall quality of the corn. This is the step where a large majority of kernel damage can occur. If the rotor speed is too high, and the clearance to small, an excessive amount of kernel damage can occur. It is suggested at the beginning of the growing season to set the speed to minimum to reduce kernel damage. Increase speed in 25 rpm increments, if too many kernels are left on the cobs. Ideally, the speed should be set low enough that you would occasionally be able to find a kernel left on the cob. This creates a balance between lost grain still on the cob and sustaining extensive kernel damage.

At the start of the season, set the concave at the widest setting. Check for losses through the system or high amount of kernels on cobs and adjust smaller in increments until losses are at a minimum. Remember, in dry years, the clearance should be set smaller for smaller ear sizes. Our goal with concave settings is to manage the flow of materials through the system. If the clearances are too large, grain may not be removed adequately, but set to tight will cause damage to kernels.

To maintain the highest amount of throughput as well as reduce damage to kernels, it is usually optimum to keep the rotor and concave full of grain. However, it may be difficult to achieve that in years such as this one. It will be important to keep making small adjustments throughout the growing season to walk the line between adequate threshing and kernel damage. This will change from field to field and even within fields.


The majority of cleaning occurs with the initial blast of air coming off the pan. Because of this, it is essential to have a uniform distribution of grain feeding off the pan and onto the sieve. To appropriately set the fan, initially set it to the highest setting. If grain is being thrown out the back, reduce it incrementally until no more grain is blown out the back, but the fan is still at the highest reasonable setting. Getting the most possible trash out with the fan prevents kernels from being caught and carried out over the cleaning shoe or straw walkers. Additionally, check the tailings to make sure there are a relatively few number of whole kernels there. If there are too many, open the sieves slightly more. Again, with smaller ear and kernel sizes, the opening of the sieve should be smaller. Unfortunately, this could result in more kernels recirculated through the tailings and possible kernel damage. Find a balance between retaining smaller kernels and not recirculating larger kernels.

Check how you are doing

At the beginning of the season, and periodically throughout, particularly as conditions change, it is important to check how the combine is performing. Begin harvesting forward into a pass. After a little bit, stop and back up. Check the space between the head and the standing crop. How many ears are being lost out of the head? In 1/100th of an acre, one dropped ear is the equivalent of 1 bushel per acre lost. Now check behind the combine. Move residue away to get to the soil surface. How many individual kernels can you find in 1 square foot? The total number of kernels per square foot, divided by 2, equals the number of bushels per acre loss. So if you find 30 kernels on the ground in one square foot, that would mean a loss of 15 bushels per acre. At this point it is important to note where the majority of the loss is coming from? Is the majority of the loss before it even gets in the combine? What adjustments need to be made to get those ears in the head? How big of a loss is occurring out the back of the combine? Are there settings that can be adjusted to compensate? Standards from The American Society of Agriculture and Biological Engineers say that 1% is the acceptable threshing loss. That doesn’t provide a large margin for error.

Checking all these settings takes time. However, when we stop to think of all the losses compounding, it certainly adds up. Say we had 2 ears in 1/100th of an acre loss from the head, and another 1.5-2 bushels per acre loss from the threshing process as well as some damaged kernels from improper rotor speeds. That adds up to over 5 bushels pretty easily. And while the price of corn isn’t high, $20 per acre might be worth the 15-20 minutes it takes to check these settings a couple times during the harvest season.

Conditions Matter

Finally, as we move closer to harvest, we have the conditions necessary to result in weak stalks and ear shanks as well as development of stalk rots and ear molds. It is vital that we check fields routinely to prioritize fields that may be susceptible to lodging or poor ear retention in order to not have any more issues than necessary. As fields approach physiological maturity or black layer, moisture will be around 30%. Each day will result in a half a point reduction in moisture. Keep on top of these assessments, and get crops out the field as soon as possible. Changes in environmental conditions are also going to affect how the crop feeds through the system. After you get the combine set for the first time during harvest, conduct the same evaluation system again in new fields, and particularly as conditions change.


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