Combine settings and operation are critical to minimize harvesting losses. The combine is a complex machine that gathers, threshes, and cleans the grain. Poor combine adjustment can result in not only lost yield, but reduced grain quality as well. When set properly, most combines, both cylinder and rotor types, can do a good job of preserving yield while separating kernels from the non-grain portion of the crop.
Growers are advised to set the combine to manufacturer-recommended settings as a starting point, and then adjust to the condition of the crop. Frequent checking and readjusting can then keep the combine set appropriately to reduce both harvest losses and kernel damage. When crop conditions change during the day, small adjustments may be necessary.
The goal of proper combine settings is to achieve a smooth, even flow of crop material moving through the machine. The combine should run nearly full to minimize impact on the grain. A near-empty machine, on the other hand, leads to multiple contacts of the machine and the grain, which increases breakage.
Gathering snouts: Adjust snouts so that they just touch the ground under normal conditions. If plants are lodged, let snouts float on the ground and reduce ground speed as needed.
Snapping roll and stripper plate spacing: Set snapping roll spacing according to stalk thickness. Set the stripper plates (aka, deck plates or snapping bars) as wide as possible without losing ears or shelling corn off the ear (this reduces amount of stover taken into the machine). Plates should be set slightly narrower (1/8 to 3/16 inches) in front than in back to prevent wedging. If ears are small in diameter due to drought, narrow the stripper plates accordingly so ears are not pulled through and lost.
Ground and snapping roll speed: The ground speed depends on the condition of the crop, but should generally be as fast as possible without plugging the head or threshing mechanism. Snapping rolls should be set relative to ground speed. When set too fast, snapping rolls increase the impact of the ear on the stripper plates. This causes kernels to be shelled and lost, increases breakage of ear butt kernels and results in ear bounce.
Cylinder/rotor and concave: The cylinder or rotor is designed to thresh corn from the cob. It is no surprise then, that cylinder/rotor speed is the leading cause of grain damage by the combine. In one study, increasing the cylinder speed from 300 to 600 rpm increased kernel damage from below 5% to over 30%. However, if threshing is too gentle, unshelled kernels can be lost with the cobs.
Growers should use the lowest possible cylinder/rotor speed that will shell the grain within acceptable loss levels (less than 1% in good-standing fields). To reduce unthreshed losses without increasing grain damage, try decreasing the concave clearance before increasing cylinder/rotor speed. If this does not achieve satisfactory threshing, then begin to increase cylinder/rotor speed as required.
Concave clearance should be set so as to avoid breaking the cobs excessively, which can lead to kernels left on cob fragments. Cobs should only be broken into 3 or 4 pieces for best threshing results and minimal threshing losses.
Separation and cleaning: After threshing, the grain is separated from non-grain crop material by the chaffer and shoe sieves and the cleaning fan. Lighter chaff is blown out the back of the combine, while heavier unthreshed cob segments are returned to the thresher by the tailings system. Screens allow fine grain particles and foreign matter to be removed in the cleaning process.
The goal of separation and cleaning is to achieve a clean, high-quality end product while minimizing grain losses. To accomplish this, sieve and fan settings are critical. If the fan speed is too high, kernels will be lost. If too low, excess foreign material is retained in the grain. Begin with manufacturer suggested settings and check and adjust frequently. Crop conditions, including non-grain crop moisture, can change rapidly during autumn days. Monitor losses behind the combine and grain quality in the grain tank throughout the day.