Strategies for improving corn harvest efficiency

With the warm, dry weather this growing season, corn harvest may be earlier than expected. While harvest efficiency is important every year, it will be especially critical this year with potentially lower yields due to higher temperatures and below-average rainfall in some areas (Figure 1). Producers spend considerable time and money to protect their corn yield. However, some of the biggest yield losses can occur during harvest operations.


Figure 1. The hot, dry weather in 2018 has reduced pollination and grain fill, potentially reducing the yield. Photo by Gretchen Sassenrath, K-State Research and Extension.


Harvest inefficiency can reduce overall yield and can cause future problems because of volunteer corn (Figure 2). Volunteer corn may have some value by increasing the soil organic matter, providing coverage to reduce soil erosion, or providing potential forage for grazing livestock. However, volunteer corn may cause problems for wheat planting following corn harvest, or in a wheat-corn-fallow cropping system by using valuable soil moisture and nutrients needed to promote fall tillering in wheat. Volunteer corn can also provide a “green bridge” of vegetation for insects that can carry viral diseases to wheat.


Figure 2. Extremely thick stand of volunteer corn, resulting from grain lost during harvest operations. Photo by Gretchen Sassenrath, K-State Research and Extension.


The biggest problem with having a dense stand of volunteer corn is that it indicates a significant loss of corn grain during the harvest operation. It will never be possible to harvest 100% of the grain. However, it is possible to improve the efficiency of harvest and the yield by paying careful attention to harvest operations. By taking steps to improve the harvest efficiency, grain loss can be reduced.

Several factors may contribute to poor harvest efficiency in corn. Most of the kernel loss that occurs at harvest time is due to mechanical limitations with combine settings. A combine performs three major actions during the harvest operation: picking, threshing and cleaning. Grain loss can occur at each of these stages. A detailed description of harvesting efficiency can be found in the KSRE publication “Corn Production Handbook” ( beginning on page 36.

Estimating yield loss

Yield loss estimates are made by counting the number of kernels per square foot and dividing by 2 (Figure 3). The number of kernels per square foot is approximately twice the bushels per acre lost. To estimate the yield loss, count the number of kernels in a square foot, and divide by 2 (or multiple by 0.5). For example, a count of 20 kernels per square foot would indicate 10 bu/acre lost during harvest.

While it may be time-consuming to count kernels over a large area, it is important to get a good estimate of yield loss by counting kernels and ears from several locations in the field, and also to include both header and thresher losses. Changes can then be made in the harvest operation and to the combine to improve the harvest efficiency. It is also important to check for field losses at different times of the day when harvesting and on different fields. Changes in weather conditions (moisture and temperature) or other factors may impact harvest efficiency.

Figure 3. Estimate corn loss during harvesting by counting the number of kernels in a square-foot area. The number of kernels per square foot is approximately twice the number of bushels per acre lost. Count the number of kernels and divide by two – this is the bushel/acre yield loss. Several areas in a field should be checked. Photo by Gretchen Sassenrath, K-State Research and Extension.


Combine settings

Ground speed is one of the most important factors that a combine operator can control to improve harvest efficiency. By matching combine ground speed to crop throughput and harvest conditions, the operator can improve harvest efficiency. Excessive ground speed results in greater losses at almost all stages of the harvesting operation. Ground speed that is too slow may fail to keep the combine operating at full capacity, decreasing the threshing efficiency, and increasing the specific fuel consumption (gallons/bu).

Header loss

Header loss occurs when kernels do not make it into the machine. Both biological and mechanical factors contribute to header loss. Corn that has lodged or is too dry may shatter, causing whole ears to be lost. Deck plates that are set too widely may cause excessive butt shelling of the ears. Adjusting both the header speed and relative ground speed can reduce header loss; slower may be better.

To measure header loss, harvest a portion of the field and then place a marker toward the rear of the combine and in front of the tailings discharge. Back the machine up so that the front of the header is even with the marker. Grain on the ground in the area between the header and the unharvested portion of the field is due to header loss. To determine the loss per acre, count the number of kernels or ears on the ground between the front of the combine and the unharvested corn and estimate the yield loss.

Adjustments to minimize header loss

  1. Adjust the gathering snouts so that the center snout is just touching the ground when the gathering chains are 2 inches above the ground. Working out from the center, each successive snout should be about 1 inch lower than the adjacent snout. Drive with the center snout just touching the ground. This will insure that all snouts float at ground level when combining over rough ground.
  2. Gathering chains should extend at least ¼ inch beyond the snapping plate when measured at the front of the plate. Control chain speed so that stalks are guided into the rolls without uprooting.
  3. Snapping rolls should be set according to stalk thickness with speed correlated closely to ground speed so that the ear is snapped in the upper third of the roll. This helps reduce ear loss.
  4. Deck plates should be set as wide as possible without losing ears or shelling corn off the ear. This reduces the amount of trash taken into the machine. The spacing between the plates should be 1/8 to 3/16 inch tighter at the front of the plates than at the rear. In highly variable crop conditions, paying close attention to deck plate spacing has one of the largest potentials for payback. Newer headers with automatic or hydraulically actuated deck plates have the potential to significantly reduce header losses.
  5. Trash knives should usually be set as close to the rolls as possible to prevent wrapping.

Threshing loss and kernel damage

As with most other crops, cylinder or rotor adjustment has a great effect on corn quality. As much as 80% of corn kernel damage occurs during the shelling process, so careful management at this point will produce dividends throughout storage and drying. Moisture content has a large effect on the amount of damage, with fines increasing rapidly at high moisture. If possible, delay harvest delayed until moisture is between 20-25%.

Concave clearance and cylinder or rotor speed require careful adjustment, and although a great variation in hybrids exists, a few rules of thumb have been developed. Over-shelling the grain (by having the cylinder or rotor speed too high, or the clearance too tight) not only produces excess fines, but also consumer excessive power and fuel. A good way to adjust the cylinder or rotor is to begin with the clearance and speed recommended by the manufacturer (or in the middle of the suggested range), then make small changes after checking the discharge of the machine.

Adjustments to minimize threshing loss and damage

  1. Concave clearance should be set so that cobs fracture into halves or pie-shaped segments. If the cobs are broken into smaller halves or quartered pieces, higher cylinder or rotor speeds will be necessary to remove the grain, which in turn can contribute to grain damage, loss, and decreased sample quality.
  2. Reduce cylinder or rotor speed to the point that an occasional kernel is left on the cob. Several studies have shown that the best compromise between unshelled grain and excessive kernel damage occurs when about 0.2% of the kernels remain on the cob.

Keep in mind that the most significant contributing factor to grain damage is cylinder or rotor speed. In addition to grain damage, excessive cylinder or rotor speed can lead to increased levels of foreign material in the grain sample.

Sieve and chaffer settings

Machinery settings can affect grain losses at the sieve and chaffer. Grain losses may be reduced by adjusting fan speed. If there is too much trash, the kernels stay in the trash through the straw walkers in a conventional combine or over the cleaning shoe in a rotary design. The kernels are then thrown out of the machine in the tailings. This can results in a windrow effect when the corn kernels germinate (Figure 4).


Figure 4. Windrowing effect from grain loss directly behind the combine. Photo by Gretchen Sassenrath, K-State Research and Extension.


Careful adjustment of the combine can improve this. If the air speed is too high, too many kernels are lost. Conversely, if air speed is too low, unnecessary foreign material is retained in the grain resulting in quality dockage at the point of delivery. Adjust chaffer and sieve to minimize grain losses in the tailings. Yield losses from cleaning operations can be measured by counting kernels behind the combine. Especially look for windrowing effects if an adequate spreader is not used.



Efficiency at each stage of the production cycle is important for growing and harvesting the best yield possible. In challenging years such as 2018, it is especially critical to be aware of equipment calibration to increase the harvest efficiency.

In addition to the combine losses described here, additional losses can occur during transfer events. While this may look substantial, it is usually not very high across the entire field.

There is a free mobile app from Ag PhD available to estimate harvest losses based on the kernel count per square foot. The download links are here:  iOS  and Android. The app allows the user to select the crop and input the number of seed or kernels counted from an area on the ground. Harvest loss is calculated from this count.

While harvest efficiency will never be 100% and it is important to complete the harvest in a timely fashion, paying attention to details during harvest can increase profitability. A normal harvest loss rate to aim for is 1 to 2%. Careful attention to equipment, harvest conditions, and harvest operations can minimize yield losses at harvest time and put more corn in the bin.

Additional information is available in the KSRE publication “Corn Production Handbook” (


Gretchen Sassenrath, Crops and Soils Agronomist, Southeast Research and Extension

Lucas Haag, Northwest Crops and Soils Specialist

Xiaomao Lin, State Climatologist

Lonnie Mengarelli, Research Assistant, Southeast Research and Extension